Beginner Seasoned
Pick your zone and the dates re-calibrate.
The Guide Crops Vol. 003

Kohlrabi

in Zone 9, this week

Kohlrabi is a cool-season cabbage-family vegetable grown for its odd, tasty swollen stem, a round bulb, green or purple, that sits right on top of the soil with leaves sprouting from it. It is one of the fastest crops in the garden, ready in about 45 to 60 days, and grows best in the cool weather of spring and fall. The trick is simple: keep it growing steadily with even water, and pick the bulb young, about the size of a tennis ball. If you let standard kohlrabi get too big, or let it dry out or cook in summer heat, it turns woody and tough. It handles frost well, and like its cabbage cousins it gets the usual cabbage-family bugs and diseases. The bulb is crisp and mild, good raw or cooked. Kohlrabi (Brassica oleracea, Gongylodes group) is a cool-season cole crop grown not for a head or a root but for its swollen above-ground STEM, a round, pale-green or purple bulb that sits on the soil surface topped by a rosette of leaves. It is one of the fastest brassicas, ready in about 45 to 60 days, and is grown like a quick cabbage in the cool shoulders of spring and fall. The whole craft is steady, unchecked growth and timely harvest: a tender, mild, crisp bulb forms when the plant never stalls, while drought, heat above roughly 75°F, or a stop-start water supply, or simply letting it grow too large, turns standard types woody, fibrous, and bitter. Harvest young at 2 to 3 inches, tennis-ball size; giant storage cultivars (Kossak, Superschmelz) are the exception and hold tender flesh at a much larger size. Cold-hardy and frost-tolerant, kohlrabi shares the full cabbage-family pest and disease complex.

Kohlrabi mature plant
Fig. 01 · Kohlrabi, mature Zone 9
Mature in
45-60d
from transplant
Sunlight
Full sun
6-8 hrs daily
Water
Regular
1.5 inches / week
Spacing
6 to 8 in
between plants
Soil pH
6-7
slightly acidic
Today · in your zone

What's happening right now

October 21 · Zone 9 · Stage 01 · Germination

Off-season for kohlrabi in zone 9.

Seasoned
Microclimate · Zone 9a vs 9b

Your zone, at a finer grain

Zone 9 averages a last frost around March 1. Within Zone 9, the colder half (9a, winters down to 20°F) runs about a week later. The warmer half (9b, winters down to 25°F) runs about a week earlier. The plant app picks your subzone from your ZIP.

SubzoneLast springFirst fallGrowing daysWinter minFruits reliably
9aMar 8Nov 24~26120-25°FYes · two seasons
9bFeb 28Nov 30~27525-30°FYes · two seasons

Averages from 8 weather stations per subzone, drawn from NOAA 1991-2020 Climate Normals. Your actual frost date can vary by up to two weeks based on elevation, proximity to water, and local topography.

Source: NOAA 1991-2020 Climate Normals Methodology
Your climate region in Zone 9
The season at a glance

Planting calendar

In Zone 9, kohlrabi can be planted August through September, then again December through February, skipping the summer heat. Start indoors Nov 1 - Nov 22. Harvest runs March through May.

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
plant
plant
plant
too late
too late
too hot
too hot
indoors
plant
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indoors
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harvest
harvest
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harvest
harvest
harvest
indoors
plant out
harvest
Get a head start indoors It is too hot for kohlrabi to grow well outside right now, but you can start seeds indoors now for a fall crop. Move them outside once daytime highs cool to around 75°F.Too hot for kohlrabi to grow well outside now. Start seeds indoors for a fall crop. Set transplants out once daytime highs cool to about 75°F.
Seasoned
Extend the harvest in zone 9+

A second planting

Plant kohlrabi in small batches every couple of weeks instead of all at once, since each plant gives one bulb. Grow it in spring and again in late summer for fall, and skip the hottest part of summer.Kohlrabi is fast (about 45 to 60 days) and each plant makes a single bulb, so the way to a steady supply is small, frequent sowings rather than one big planting. Sow in batches every 2 to 3 weeks across the spring window and again in late summer for fall, skipping the high heat of summer, when the stem turns woody and bitter. The fall crop, sizing in cooling weather, is often the most dependable.

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1plant
plant
plant
indoors
plant
harvest
harvest
harvest
2plant
indoors
plant
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harvest
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plant out
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harvest
1Main crop
2Second planting
The season, mapped

Seed to garden

You can sow kohlrabi seeds right in the garden or start with young plants. For direct sowing, plant the seeds about a quarter to half an inch deep once the soil can be worked, then thin the seedlings to about 6 to 8 inches apart. For transplants, start seeds indoors about a month before planting out, and set them in the garden a week or two before the last frost. Let homegrown seedlings get used to the outdoors over a week before planting. Sow again in mid-summer for a fall crop.Kohlrabi is grown both ways. Direct sowing is simple and common since the crop is fast: sow 1/4 to 1/2 inch deep once the soil is workable and thin to 6 to 8 inches apart. For an earlier or more uniform crop, start transplants indoors about 4 to 5 weeks before set-out and plant them out 1 to 2 weeks before the last frost, since young plants take light frost. Avoid exposing young plants to a long cold spell (more than about a week of nights below roughly 45 to 50°F), which can trigger bolting. Sow the fall crop in mid-summer. Harden transplants off over 7 to 10 days.

  1. 01
    Sow indoors →
    Nov 1 - Nov 22
    Start about 4 weeks before your last frost
  2. 02
    Transplant out →
    Dec 1 - Feb 28
    After hardening off
  3. 03
    First harvest
    From Mar 1
    45-60 days from transplant
Start method
Both
Soil temp
45-85°F
Hardening off
7-10 days
From seed to fruit

The growing journey

Stage 01 · Germination
01
Germination
Days 5-12 · current stage
In about 5 to 10 days, your seeds sprout and push up their first two little leaves, called seed leaves.Seeds sprout in about 5 to 10 days at soil temperatures of roughly 60 to 75°F, pushing up two seed leaves (cotyledons).
Keep the soil damp and warm. Once you see the first real kohlrabi leaves after the seed leaves, thin out crowded seedlings.Keep the seedbed or starting mix evenly moist and warm; thin or pot up once the first true leaves appear.
FROM PLANT · Plant the seeds about a quarter to half an inch deep in damp soil, and keep it evenly moist while they sprout.Sow about 1/4 to 1/2 inch deep into a moist seedbed or starting mix; kohlrabi germinates fast and reliably across a wide soil-temperature range as long as moisture stays even.
FROM PLANT · Kohlrabi grows fast, so you can plant the seeds right in the garden. Starting indoors is only needed if you want an earlier crop.Because kohlrabi is so quick, direct sowing works well; start transplants only when you want an earlier or more uniform stand.
02
Seedling
Days 10-25
The seedlings grow their real leaves and a stronger stem. Direct-sown plants are thinned now; transplants are ready to move outside at about 4 to 5 weeks old.Young plants develop true leaves and a sturdy stem; transplants are ready at about 4 to 5 weeks, and direct-sown stands are thinned to spacing.
Thin direct-sown seedlings to about 6 to 8 inches apart. Before planting transplants outside, harden them off over about a week, and avoid setting them out into a long cold snap.Thin to 6 to 8 inches; harden off transplants over 7 to 10 days and avoid exposing young plants to a prolonged cold spell, which vernalizes them and triggers bolting.
FROM PLANT · Thin the seedlings to about 6 to 8 inches apart so each one has room to form a good bulb.Thin to 6 to 8 inches apart; crowded plants make small, misshapen bulbs and compete for moisture.
FROM PLANT · Do not plant young kohlrabi out into a long cold spell, which can make it flower early instead of forming a bulb. Wait for settled weather.Avoid setting young transplants out into a prolonged cold snap (over about a week below roughly 45 to 50°F), the classic vernalization trigger for bolting.
03
Established
Days 22-42
The plant puts on a rosette of broad leaves on a short stem for a few weeks. This leafy growth comes before the bulb swells.The plant builds a leafy rosette over several weeks before the stem base begins to swell.
Feed the plant a little nitrogen as it grows and keep it evenly watered. Check the leaves for caterpillars, aphids, and flea-beetle holes.Side-dress with nitrogen as the plant establishes, keep moisture even, and watch for cabbageworms, aphids, and flea beetles.
FROM PLANT · Feed the plants a little nitrogen a few weeks after planting and water steadily so they keep growing without a stall.Side-dress nitrogen about 3 to 4 weeks after planting when plants are roughly 4 inches tall, and keep moisture even; steady growth is what keeps the coming bulb tender.
FROM PLANT · Check young plants for tiny flea-beetle holes and for aphids tucked into the leaves, and keep the plants growing strong.Scout for flea beetles on young plants and cabbage aphids in the leaf axils; a vigorous, well-watered stand outgrows light flea-beetle feeding.
04
Stem swelling
Days 35-55
The base of the stem, just above the soil, swells into a round, pale-green or purple bulb. This is the part you eat.The stem base swells into the round, above-ground bulb. Even moisture and steady growth here decide whether it is crisp and mild or woody and fibrous.
Keep the water steady so the bulb stays tender, and watch its size. It is ready when it reaches about 2 to 3 inches across, the size of a tennis ball. Do not let it keep growing past that or it turns woody.Keep moisture even and check size daily as it approaches 2 to 3 inches; a growth check from drought or heat now is what turns the stem woody and bitter.
FROM PLANT · Water steadily while the bulb is swelling. Letting it dry out and then soaking it is what makes kohlrabi tough and cracked.Keep water even at roughly 1 to 1.5 inches per week as the stem swells; a drought-then-soak swing is what makes kohlrabi woody and splits it.
FROM PLANT · Check the bulb every day as it gets close to tennis-ball size. Standard kohlrabi turns woody fast if it grows too big.Watch the bulb size daily as it nears 2 to 3 inches; standard types pass their window quickly and turn woody, so do not let them oversize.
05
Harvest
Days 45-60
The bulb is about 2 to 3 inches across, the size of a tennis ball, firm and smooth. This is the moment to cut it, before it gets bigger and tougher.The bulb reaches about 2 to 3 inches in diameter (larger for the giant storage types), firm and smooth, before it turns woody.
Cut the whole bulb off at the base with a knife while it is still young and tender. Standard types get woody if you wait too long, so do not let them grow large. Harvest in the cool morning if you can.Cut the bulb at the base while young; standard varieties grow tough, woody, and bitter past about 3 inches, so harvest on time. Giant types (Kossak, Superschmelz) hold tender at larger size. Trim the tops and chill promptly.
FROM PLANT · Cut the bulb off at the base when it reaches tennis-ball size. If you wait too long it gets woody and will not get tender again.Cut the bulb at the base at 2 to 3 inches for standard types; harvest on time, since a woody, over-mature kohlrabi will not soften.
FROM PLANT · Cut off the leaves and get the bulb into the fridge, where it keeps for a couple of weeks.Trim the leafy tops and chill promptly; the bulb keeps 2 to 3 weeks refrigerated, far longer for the giant storage types.
Beginner
Know your soil

Your soil

Identify yours

Not sure what soil you have? Grab a small handful of damp soil from your garden bed and squeeze it. If it crumbles apart easily, it's sandy. If it holds together but breaks when you poke it, it's loam (what most vegetables want). If it stays in a hard, slippery ball, it's clay.

What this crop wants

Kohlrabi grows best in fertile, loose, well-drained soil with plenty of compost mixed in, and it likes steady, even moisture. The bulb stays tender and mild when the plant grows quickly without a check, so soil that holds moisture but drains well is ideal. Soil that dries out or stays soggy stresses the plant and makes the stem tough and woody.

If your soil doesn't match

You have sandy soil

Mix 2-3 inches of compost into the top 6 inches of your bed before planting. Compost holds moisture (which sandy soil drains too fast) and adds the nutrients sandy soil tends to lack. Repeat each season. Compost breaks down over time.

You have clay soil

Mix 2-3 inches of compost AND a few inches of coarse sand or perlite into the top 6 inches of your bed. The compost feeds the plants; the sand breaks up the clay so air and water can move through. Don't add sand without compost. It can compact like concrete.

Containers and raised beds

If amending your soil sounds like too much work, or if your soil is heavy clay, full of rocks, or contaminated, build over it. A raised bed at least 12 inches deep filled with a 50/50 mix of compost and sandy loam gives you ideal growing soil with no battles. A 5-gallon container with quality potting mix does the same for one plant at a time. Both bypass your native soil entirely.

Learn more about your soil
The specs

Care guide

The numbers that matter, at a glance.

Sunlight
Full sun · 6-8 hrs/day
Water
Regular
Spacing
6 to 8 inches
Soil
loam, sandy loam
Days to maturity
45-60 days from transplant
Soil pH
6 to 7
Container OK?
Yes · 3+ gal pot
Germination temp
45-85°F
In a pot

Yes, 3 gallons and up

Kohlrabi is a great container crop because it is small and shallow-rooted. Use a pot at least 8 inches deep that holds 3 to 5 gallons, with drainage holes, and space the plants about 6 inches apart. Keep it watered evenly and harvest the bulbs young.Kohlrabi suits containers well: it is compact, shallow-rooted, and quick, so a pot 8 inches or more deep holding 3 to 5 gallons grows several plants spaced about 6 inches apart. Width matters as much as depth, since you want room for several bulbs. Keep the mix evenly moist, because pots dry fast and a checked plant turns woody, and feed lightly. Provide drainage holes and a loose potting mix.

Pot size
3 gallons and up; 5 gallons is comfortable
Drainage
Drainage holes are a must. Skip the gravel layer. Do not let the pot sit in a saucer of water. Kohlrabi needs steady, even moisture, but soil that stays soggy will rot the roots, so empty the saucer within an hour of watering.Drainage holes are a must. Skip the gravel layer. Do not let the pot stand in a saucer of water. Kohlrabi needs even moisture for a tender bulb, but waterlogged mix causes rot and favors clubroot; empty the saucer within an hour of watering.
Watering
Pots dry out much faster than the ground, so check daily in warm weather. Kohlrabi turns woody if it dries out, so keep the moisture steady.Containers dry faster than beds; check moisture daily in heat and water before the mix dries out, since drying out toughens the bulb.
Depth and shape
At least 8 inches deep. Kohlrabi is a small, shallow-rooted plant, so a wide, fairly shallow container suits it better than a deep narrow one. Choose a pot at least 8 inches deep holding 3 to 5 gallons, and favor width so you can grow several plants spaced about 6 inches apart. Provide drainage holes and keep the mix evenly moist.
Self-watering pot
Yes. A self-watering container suits kohlrabi well, since it smooths out the steady moisture the crop needs to keep the bulb tender.
Mix
Container potting mix. Use a light, loose potting mix with a handful of compost for even moisture-holding. Avoid garden soil, which compacts in a pot and can introduce the soilborne clubroot pathogen.
Feeding
Container kohlrabi needs slightly more frequent feeding than in-ground plants because watering leaches nutrients from the mix.
One to try

Early White ViennaThe classic pale-green heirloom and the standard early type; quick, dependable, and best picked young at tennis-ball size.

2 more compact types

Early Purple ViennaThe purple-skinned counterpart to White Vienna, with the same creamy white flesh; the skin color is a handsome garden feature and does not affect flavor.

KolibriA vigorous purple hybrid with crisp white flesh, good bolt resistance, and a wide harvest window; popular for both spring and fall.

Pot safety

Ask what your balcony or roof can carry

A balcony or roof can only hold so much weight. Before you set heavy pots there, ask a building architect what it can safely carry.Illinois Extension's guidance is to consult a building architect about weight limits before placing heavy pots on a balcony or rooftop garden. It gives no weight figure.

Never grow food in a container with anything toxic in it

Many kinds of containers can be used. Whatever you choose, keep anything toxic out of it, especially if you are growing food.Colorado State accepts nearly any container material but warns against using a container that holds toxic materials, especially for edible plants. Illinois adds that a vegetable container should be free of chemicals toxic to plants or people, and urges caution with treated lumber when growing food. If you cannot account for what a repurposed container once held, that alone is a reason to keep food out of it.

Secure hanging containers well

Fasten hanging baskets and window or rail boxes securely. Think about what is below them too, since they can drip on people or things underneath.Illinois Extension asks growers to secure hanging containers well and to think through the safety issues of hanging them. Placement matters too, since a hanging container can drip onto people or belongings below.

Soil chemistry

Soil pH for kohlrabi

Preferred
6 to 7
Tolerated
5.5 to 7.5

Kohlrabi grows best in soil that is slightly acidic to neutral, about 6.0 to 7.0. A simple soil test tells you where you stand. If you have had clubroot, a brassica soil disease, keeping the soil closer to neutral helps hold it back.Aim for a soil pH of about 6.0 to 7.0 (Iowa State gives 6 to 7; Minnesota and Utah State put the workable range at about 6.0 to 7.5). Kohlrabi tolerates roughly 5.5 to 7.5. Clubroot, the major brassica soil disease, is favored by acidic soil below about 6.5, so where it is a concern lime acidic ground well ahead of planting and hold the pH toward neutral.

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Steady hand on the hose

Watering

When & how much
Frequency
Water regularly so the soil stays evenly moist, roughly 1 to 1.5 inches a week. Try to keep it steady, not dry-then-soaked.Give about 1 to 1.5 inches weekly, kept as even as possible; steady moisture is what keeps the bulb tender, and a dry-then-wet swing makes it woody or cracks it.
Amount
Aim for roughly 1 to 1.5 inches of water a week, a bit more in hot, dry weather.About 1 to 1.5 inches per week including rain (Iowa State and Minnesota: roughly 1 inch a week; Utah State up to 1 to 2 inches in heat or sandy soil), with the most attention while the stem is swelling.
Method
Water at the base of the plant rather than over the leaves.Water at the soil line with drip or a soaker hose where possible to keep foliage dry and discourage the leaf diseases kohlrabi shares with the cole crops.
Signs of trouble
Too much water
Lower leaves yellow and the plant looks soggy and limp.Yellowing lower leaves and limp growth; kohlrabi dislikes waterlogged soil, which invites root maggots, clubroot, and rots in cold, wet ground.
Too little water
Wilting leaves and a tough, woody bulb. Letting the soil dry out is the main thing that makes kohlrabi woody, and a sudden soaking after a dry spell can crack it.Wilting and stalled growth, then woody, fibrous, strong-flavored stems; the classic kohlrabi fault is letting the bed dry out, which toughens the bulb, and a heavy soak after a dry spell can split it.
Feeding rhythm

Feeding

Frequency
twice a season
Type
Balanced, then nitrogen
When to start
work a balanced fertilizer in before planting, then side-dress about 3 to 4 weeks later

Kohlrabi needs decent soil and a little feeding, but not a lot. Mix a balanced fertilizer into the soil before planting, then give one feeding of a nitrogen fertilizer a few weeks later when the plants are a few inches tall. Keep the watering and feeding steady so the bulbs grow smoothly and stay tender.Kohlrabi is a moderate feeder that wants steady, even growth rather than a late surge. Work a balanced fertilizer such as 10-10-10 into the bed before planting (Iowa State: 1 to 2 pounds per 100 square feet), then side-dress with nitrogen about 3 to 4 weeks after planting or thinning, when the plants are roughly 4 inches tall (Utah State: about half a cup of 21-0-0 per 10 feet of row). Keep nitrogen and water even through bulbing, since both a stall and a late flush hurt texture; avoid heavy late nitrogen, which can grow leaves at the expense of a clean bulb.

N · P · K = 10-10-10

Use a balanced fertilizer like 10-10-10 at planting, then one feeding of a nitrogen fertilizer a few weeks later as the plants take off.A balanced base feed for steady growth: work a 10-10-10 into the bed before planting, then a single nitrogen side-dress such as 21-0-0 or blood meal about 3 to 4 weeks after planting. Keep it modest and even, since pushing the plant late grows leaves over a clean, tender bulb.

Try 10-10-10 worked in before planting, then 21-0-0 or blood meal as a side-dress
Who grows well together

Companion planting

Kohlrabi gets along with most vegetables. It does well next to aromatic herbs, onions and other alliums, beets, and quick leafy greens like lettuce that finish before the kohlrabi fills out. The main thing is to keep it away from its own cabbage-family relatives, which share its pests and diseases. Most kohlrabi companion pairings are traditional rather than trial-tested. The ones worth acting on are practical: aromatic herbs and alliums as scent-based deterrents for cabbage-family pests, low quick crops like lettuce that use the open ground while the kohlrabi sizes up, and beets sharing the cool-season bed. The well-grounded caution is to separate kohlrabi from other brassicas, which share clubroot and the whole cabbage-family pest complex, a rotation and disease principle more than a tested adjacency effect. As University of Minnesota stresses, treat most companion claims as a starting point and watch your own results.

Other
Onions and other alliums
Onions, garlic, and chives grow tall and narrow with shallow roots, so they tuck between kohlrabi without crowding it, and their strong smell is widely used to help confuse cabbage-family pests.Alliums are a traditional brassica companion, their pungent scent thought to mask the crop from the cabbage pests that hunt partly by smell. Shallow-rooted and undemanding, they tuck around kohlrabi without competing for much. Treat it as a low-risk, scent-based aid rather than a proven control. Traditional
Lettuce and other leafy greens
Lettuce grows fast and low, so you can tuck it between young kohlrabi plants to use the space and shade the soil, and it is harvested long before the kohlrabi fills in. Both like the same cool weather.Lettuce and kohlrabi interplant well on structure and timing: lettuce is shallow and quick, kohlrabi a little slower, so the lettuce uses the open ground and light between young plants and is pulled before the kohlrabi canopies. It is an efficient cool-season space pairing, not a pest effect. Traditional
Beets
Beets are another cool-season crop that shares the bed easily with kohlrabi without competing for the same space, since beets put their energy down into the root while kohlrabi swells just above the soil.Beets are a traditional, low-risk cool-season neighbor for kohlrabi. They share the same season and undemanding habit, and the beet works the soil below while the kohlrabi swells at the surface, so the two coexist without much competition. A space-and-season pairing rather than a documented benefit. Traditional
Herb
Dill
Aromatic umbels like dill draw parasitoid wasps and hoverflies that attack the aphids and cabbage caterpillars kohlrabi shares with the cole crops, and the scent is traditionally said to deter cabbage pests. Let some flower, and keep it from shading the plants. Well-grounded
interplant nearby
Keep apart from
Other brassicas Keep kohlrabi away from other cabbage-family plants like cabbage, broccoli, kale, and turnips. They share the same pests and diseases, so grouping them together makes problems worse.Planting kohlrabi shoulder to shoulder with its brassica relatives, cabbage, broccoli, kale, turnip, radish, concentrates the family's shared pests (cabbageworms, loopers, flea beetles, cabbage aphids, root maggots) and shared diseases in one spot, and repeated same-family planting lets soil-borne clubroot build up. Spread brassicas out and rotate where they grow each year. Well-grounded
Pole beans A traditional caution pairs the cabbage family with pole beans as poor neighbors. There is no documented mechanism or T1 support; it persists as folklore, and the two also want different seasons. Traditional
Provenance tagged inline · see methodology for the labeling system Key
Harvest signals

When to pick

Kohlrabi is ready when the bulb is about the size of a tennis ball, 2 to 3 inches across, firm and smooth. Cut it off at the base while it is young and tender. Do not wait for it to get bigger, since standard kohlrabi turns woody and tough. Giant types are the exception and stay tender when large.Kohlrabi is ready when the swollen stem reaches about 2 to 3 inches in diameter for standard types, the size of a tennis ball, firm and smooth. Cut the bulb off at the base while it is young; past about 3 inches standard cultivars turn tough, woody, and bitter and do not recover. Giant storage types (Kossak, Superschmelz) stay tender at a much larger size. Trim the leafy tops and refrigerate promptly.

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Yield

What to expect

Each kohlrabi plant gives you one bulb, picked once. Standard types are about the size of a tennis ball; giant types can be much bigger. To get a steady supply, plant a few seeds every couple of weeks.Each plant yields one swollen-stem bulb, typically 2 to 3 inches across and a few ounces to about half a pound for standard types, harvested once. Giant storage cultivars (Kossak, Superschmelz) yield a single much larger bulb of a pound or more. There are no side shoots, so total yield is set by plant spacing and succession sowings.

Kohlrabi makes one bulb per plant, so for a steady harvest, sow a small batch every couple of weeks instead of all at once. The crop is fast, so you do not wait long.Because each plant produces a single bulb harvested at once, there is no extended peak; the way to a steady supply is succession sowing every 2 to 3 weeks across the spring and fall windows. The fast 45 to 60 day cycle makes tight succession practical. The big thing to learn with kohlrabi is to pick it young, at tennis-ball size. If you leave it to get bigger, it turns woody and tough and will not get better. Keeping the water steady also keeps it tender.The single most common first-year mistake is letting the bulb grow too big: standard kohlrabi turns woody, fibrous, and bitter past about 3 inches and does not recover, so harvest young rather than waiting for a bigger bulb. New growers also under-water, which toughens the stem.

What changes yield
Harvest timing: standard types must be cut at 2 to 3 inches before they turn woody; a late harvest ruins the bulb.Even moisture: a steady water supply keeps the stem crisp and mild, while drought or a dry-then-wet swing makes it woody and can crack it.Temperature: cool, steady growth gives tender bulbs; heat above about 75°F drives fibrous growth and bolting.Variety: giant storage types (Kossak, Superschmelz) hold tender flesh at a large size, while standard types must be picked small.Spacing and succession: yield over the season comes from spacing at 6 to 8 inches and sowing in small batches every 2 to 3 weeks.
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Pick your variety

Recommended varieties

For most gardens, pick a fast standard variety like White Vienna, Purple Vienna, Grand Duke, or Kolibri, and harvest the bulbs young, about the size of a tennis ball. Purple and green types taste the same; the purple is just prettier. If you want big bulbs, grow a giant type like Kossak or Superschmelz, which stay tender even when large.Match the type to the slot. Fast green or purple Vienna types and hybrids like Quickstar, Grand Duke, and Kolibri are the workhorses for spring and fall, picked young at 2 to 3 inches. The purple types (Purple Vienna, Kolibri) differ from the green only in skin color, not flavor. The giant storage cultivars (Kossak, Superschmelz, Gigante) are the exception to harvest-it-small: they hold tender flesh at a much larger size and suit fall and winter storage. Where clubroot is a concern, choose resistant cultivars.

Early White Vienna
The classic pale-green heirloom and the standard early type; quick, dependable, and best picked young at tennis-ball size.
Early Purple Vienna
The purple-skinned counterpart to White Vienna, with the same creamy white flesh; the skin color is a handsome garden feature and does not affect flavor.
Grand Duke
An award-winning green hybrid that is uniform, slow to turn woody, and a reliable all-around choice.
Kolibri
A vigorous purple hybrid with crisp white flesh, good bolt resistance, and a wide harvest window; popular for both spring and fall.
Quickstar
One of the fastest types, a green hybrid bred for tender early bulbs, good for tight succession sowings.
Kossak
A giant storage type whose large green bulbs stay crisp and tender, with little of the woodiness that oversized standard kohlrabi develops; good for fall and winter keeping.
Superschmelz
An heirloom giant that can reach 8 to 10 inches across and still stay sweet and tender, an exception to the pick-it-small rule; a long-season fall crop.
Off the vine

Storing your harvest

Room temp
Kohlrabi does not keep well on the counter. Cut off the leaves and put the bulb in the fridge soon after picking.Kohlrabi keeps a day or two at room temperature but softens and loses crispness, so refrigerate it soon after harvest. Twist or cut off the leafy tops first, since they pull moisture from the bulb.
Fridge
Trim off the leaves and store the unwashed bulb in a loose plastic bag in the fridge crisper, where it stays good for about 2 to 3 weeks. Use the leaves within a few days.Remove the leaf stems and store the unwashed bulb in a perforated or loose plastic bag in the crisper, where it keeps well for about 2 to 3 weeks (Utah State and Iowa State). The leaves keep only a few days and are best used fresh.
Freezer
To freeze kohlrabi, peel and dice it, boil the pieces about 2 to 3 minutes, cool them quickly in ice water, drain, and freeze. The quick boil keeps the flavor and texture.Kohlrabi freezes well once peeled, diced, and blanched about 2 to 3 minutes, then cooled in ice water, drained, and frozen. Blanching halts the enzymes that would otherwise cause off-flavors and texture loss in storage.
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When something goes wrong

Common problems

01 of 04
What happened You cut the bulb and it was tough, woody, and stringy instead of crisp and tender. This usually means it grew too large, since standard kohlrabi turns woody past about 3 inches, or that the plant got stressed by dry soil or heat and grew fibrous. It is tempting to leave kohlrabi to get bigger like a turnip, but with standard types that backfires. Next time, harvest at tennis-ball size, keep the water steady, and try a giant type like Kossak if you want big tender bulbs.The bulb was woody, fibrous, and strong-flavored rather than crisp and mild. The usual causes are over-maturity (standard types lignify past about 3 inches) and growth checks from drought or heat that drive fibrous tissue. Growers often leave kohlrabi to size up like a root crop, which ruins standard cultivars. Next time harvest standard types at 2 to 3 inches, hold even moisture, and use a giant storage cultivar (Kossak, Superschmelz) where a large tender bulb is wanted. Next season Pick standard kohlrabi young, at 2 to 3 inches, keep the soil evenly moist, and grow a giant variety if you want larger bulbs.Harvest standard types at 2 to 3 inches, keep moisture even, and switch to a giant non-woody cultivar for larger bulbs.
02 of 04
What happened The plant sent up a flower stalk instead of making a bulb. Kohlrabi flowers early when young plants get chilled for a stretch (more than about a week of cold nights) or when summer heat and long days push it, and once it bolts no good bulb forms. A common mistake is planting too early into a cold snap. Next time, wait for settled weather to plant, grow a bolt-resistant variety, and time the crop for steady cool growth.The plant ran to flower instead of swelling a stem. Kohlrabi bolting is largely a vernalization response, a young plant chilled below roughly 45 to 50°F for a week or more is triggered to flower, and summer heat and long days add to it. The classic cause is an early spring set-out into a cold spell. Next time avoid exposing transplants to a prolonged cold snap, time the crop for steady cool growth, and use bolt-resistant cultivars. Next season Plant into settled weather, not a cold snap or into summer heat, and choose a bolt-resistant variety like Kolibri.Avoid a prolonged cold spell on young plants, time for steady cool growth, and choose bolt-resistant varieties.
03 of 04
What happened The bulb cracked open. This comes from uneven watering: when the soil goes dry and then gets a big drink or a heavy rain, the bulb takes up water fast and splits. Next time, keep the watering steady so the soil never swings from bone dry to soaked, and harvest on time rather than letting bulbs sit oversized.The bulb split from uneven moisture: a rapid water uptake after drought stress ruptures the swollen stem. Next time hold steady moisture through bulbing and avoid the dry-then-flood cycle, and harvest on time so bulbs are not standing past size when a rain comes. Next season Keep the soil evenly moist and avoid a sudden soaking after a dry spell.Hold steady moisture through bulbing and harvest on time to avoid the dry-then-flood split.
04 of 04
What happened The plant grew plenty of leaves but never formed a real bulb. This usually comes from plants set too close together, too much shade, or a lot of nitrogen late on, all of which push leafy growth over the bulb. Next time, thin to 6 to 8 inches, grow in full sun, and keep feeding modest and even.The plant made foliage but no usable swollen stem. The usual causes are crowding, insufficient light, or excess late nitrogen, each favoring leaves over the bulb. Next time thin to 6 to 8 inches, site in full sun, and keep nitrogen modest and front-loaded so the plant transitions to bulbing. Next season Thin to 6 to 8 inches, grow in full sun, and go easy on nitrogen late in the crop.Thin to spacing, give full sun, and keep late nitrogen modest so the plant bulbs up.
The usual suspects

Pests & diseases

Pests
Cabbageworms, loopers, and diamondback moths
P · 01
Symptoms You'll see ragged holes chewed in the leaves, green caterpillars on the plant, and dark droppings. The leaves are part of why you grow kohlrabi well, and the caterpillars can also chew the bulb.Ragged holes chewed in the leaves with green caterpillars and dark frass; heavy feeding sets young plants back and the larvae can score the bulb. Imported cabbageworms are velvety green, loopers move in a looping arch, and diamondback larvae are small and wriggle when disturbed. Cause These are caterpillars that hatch from eggs laid by white butterflies and small moths. They love cabbage-family plants like kohlrabi and chew the leaves.The larvae of the imported cabbageworm, cabbage looper, and diamondback moth feed on brassica foliage; the adults are white or brownish butterflies and moths that lay eggs on the leaves. Kohlrabi is a primary host. Organic treatment Spray Bt, which is low in toxicity to people, pets and bees and acts on caterpillars rather than on insects in general, or spinosad. Bt cannot tell a pest caterpillar from a butterfly one, so treat only the plants that have a problem. Pick caterpillars and eggs off by hand from under the leaves. Spray again after rain.Spray Bt (Bacillus thuringiensis kurstaki) or spinosad, which target caterpillars and spare beneficials, and hand-pick larvae and eggs from leaf undersides. Repeat after rain, since Bt breaks down. Prevention Cover plants with a light fabric row cover after planting to keep the butterflies and moths from laying eggs, clear away old cabbage-family plants, and watch for the first white butterflies.Use floating row cover or fine mesh from planting to exclude the egg-laying adults, clean up brassica debris that shelters pupae, and scout for the first white butterflies as a spray cue.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Garden sanitation

    Clear away old cabbage-family plants when a crop is finished. The caterpillars pass part of their life cycle as pupae, a resting stage, sheltered in that leftover debris, so hauling it off leaves fewer moths and butterflies to start the next round.Removing spent brassica material takes out the debris that shelters pupae between plantings, trimming the local population of imported cabbageworm, cabbage looper and diamondback moth before the next crop goes in.

  2. Floating row cover

    Put a light fabric row cover over the plants right after planting. It lets in light and water but keeps the white butterflies and small moths from landing to lay eggs, and eggs they cannot lay are caterpillars you do not have to deal with.Cover from planting with floating row cover or fine mesh to exclude the egg-laying adults of all three species at once. Kohlrabi is a primary host, so the exclusion window matters from the day the crop goes in.

  3. Handpicking

    Walk the rows and pick caterpillars and their eggs off the undersides of the leaves. The leaves are part of what makes kohlrabi worth growing, and the caterpillars can chew the bulb too, so a regular pass pays off.Hand removal of larvae and eggs from leaf undersides catches them at the stage that has done the least damage, and it is practical at garden scale, where heavy feeding sets young plants back and larvae can score the bulb.

  4. Bacillus thuringiensis (Bt)

    Spray Bt, a caterpillar-specific control that carries low toxicity for people, pets and bees. It cannot tell a pest caterpillar from a butterfly's, so keep it to the plantings that actually have caterpillars on them. Watching for the first white butterflies tells you when to start, and spray again after rain washes it off.Bt kurstaki targets caterpillars and spares beneficials. It breaks down, so reapply after rain, and take the arrival of the first white butterflies as the cue to begin. Because it acts on caterpillars as a group, confine applications to plantings that actually carry the pest.

  5. Spinosad

    If Bt and hand-picking are not keeping up, spinosad is the stronger organic option. Spray toward dusk, when bees are not out foraging, and follow the label.Spinosad is the escalation once the softer rungs have not held. Like Bt it does most against young larvae, and timing it to dusk limits exposure to foraging bees.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Cabbage aphids
P · 02
Symptoms You'll see clusters of small gray-green insects with a dusty, waxy coating on the new growth and tucked into the folds of the leaves. Leaves may curl and there can be a sticky film.The gray-green, waxy-coated cabbage aphid forms dense colonies on growing tips and leaf undersides and in the leaf axils, curling and distorting the foliage and weakening young plants; heavy colonies foul the crop with honeydew. Cause Cabbage aphids are tiny insects that suck the plant's juices and breed fast. They love cabbage-family plants like kohlrabi and hide in the leaf folds.Brevicoryne brassicae, a brassica-specialist aphid, sucks sap and reproduces rapidly; winged forms move in from cruciferous weeds and other brassica crops. The turnip aphid can also occur. Organic treatment Knock colonies off with a strong spray of water and hit the undersides of leaves with insecticidal soap or neem oil, repeating every few days. Welcome ladybugs and lacewings.Dislodge colonies with a strong jet of water and spray insecticidal soap, neem, or horticultural oil with thorough coverage of leaf undersides; repeat every few days. Conserve natural enemies (parasitoid wasps, hoverflies, ladybugs). Prevention Check the growing tips and leaf folds often and act early. Go easy on nitrogen, since soft growth draws them, and clear away old cabbage-family plants after harvest.Scout growing tips and leaf axils weekly and catch infestations early. Avoid excess nitrogen, use row cover on young plants, and destroy crop debris that carries them over.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Balanced nitrogen feeding

    Go easy on nitrogen fertilizer. It pushes out soft, sappy new growth, and that is what draws these aphids and lets them build up fastest.Excess nitrogen produces the succulent growth this brassica specialist colonizes preferentially, so a restrained feeding program removes that flush without holding the crop back.

  2. Garden sanitation

    Pull out old cabbage-family plants after harvest instead of leaving them standing. The aphids carry over on that leftover material and move straight onto the next planting.Destroy brassica crop debris promptly, since it carries colonies between crops. Winged forms also move in from other brassica plantings, so a cleared bed removes one nearby source.

  3. Floating row cover

    Keep young plants under a light fabric row cover so winged aphids cannot land and start colonies while the plants are small. Check the growing tips and the folds where the leaves meet the stem often, so anything that does get in is caught early.Cover young plants to block the winged colonizers, and scout the growing tips and leaf axils weekly. Catching a colony early is what keeps it from lodging in the folds, where coverage is hardest to achieve later.

  4. Water spray

    Knock the clusters off with a strong jet of water from the hose, aiming into the leaf folds where they hide. Repeat every few days while you keep finding them, and do it early in the day so the leaves dry.A forceful jet dislodges colonies before they settle deep into the axils. It is a purely physical knockdown that leaves the natural-enemy complex untouched; spray early enough in the day that foliage dries.

  5. Beneficial predators

    Make the helpful insects welcome. Ladybugs and lacewings eat aphids, so give them time to find a colony and skip broad sprays that would take them out along with the pests.Conserve the parasitoid wasps, hoverflies and lady beetles that regulate this aphid. Broad-spectrum material removes them and leaves a rapidly reproducing pest with a clear field.

  6. Insecticidal soap

    Spray insecticidal soap onto the aphids themselves, coating the undersides of the leaves, and repeat every few days. It works where it wets them, and the dusty, waxy coating on these aphids means soaking the clusters rather than misting the plant.Soap kills on contact, so thorough coverage of leaf undersides and axils decides the outcome. The waxy bloom on Brevicoryne colonies is what makes deliberate, repeated application necessary.

  7. Neem oil

    Neem oil is another spray for coating the colonies. Hit the same hidden spots under the leaves and in the folds, repeat every few days, and skip it in high heat or when plants are dry at the roots.Neem is the coverage-dependent alternative to soap on these colonies. The same thoroughness applies, and it spares beneficials once it has dried.

  8. Horticultural oil

    Horticultural oil, a light spray oil, can also coat the aphids it reaches. Cover the undersides and the leaf folds the same way, and avoid spraying it in hot weather.Horticultural oil rounds out the contact options alongside soap and neem. Whichever you pick, coverage of the undersides and axils matters more than the choice of product, and it is worth holding off in high heat or on water-stressed plants.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Flea beetles
P · 03
Symptoms Lots of tiny round holes in the leaves of young plants, made by small dark beetles that jump away like fleas when you get close. Bad damage can stunt seedlings.Tiny round shot-hole pits chewed in the leaves of young plants; the small dark beetles jump like fleas when disturbed. Heavy feeding stunts seedlings and slows establishment, the costly stage for a fast crop. Cause Flea beetles are small jumping beetles that chew on young cabbage-family leaves. They hurt seedlings most, because a tiny plant can't grow fast enough to recover.The crucifer and striped flea beetles chew the foliage of young brassicas; they overwinter in debris and field edges and are most damaging at the seedling stage and in spring, easing as the season warms, so fall crops face less of them. Organic treatment Cover young plants with a row cover, and if there are a lot of beetles, use a spray such as spinosad or a kaolin clay coating. The main goal is to get the seedlings big enough to handle it.Protect seedlings with row cover and spray spinosad or apply kaolin clay if pressure is high; the goal is getting plants past the vulnerable seedling stage. Prevention Cover seedlings with row cover from the start, keep them strong with steady water and food so they grow past the damage, and pull nearby weeds in the cabbage family.Use row cover from sowing or transplanting, keep seedlings vigorous with even water and feeding so they grow through the damage, clean up weedy brassica relatives, and favor fall plantings, which see lighter pressure.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Clearing the weeds that host it

    Pull the cabbage-family weeds growing near the bed. Those weeds feed the same beetles, so clearing them leaves fewer waiting for your seedlings.Weedy brassica relatives sustain the crucifer and striped flea beetles between crops, so clearing the bed and its edges removes a standing host bridge to a young planting.

  2. Timing the planting

    Where you have the choice, lean on fall plantings. These beetles do their worst in spring and ease off as the season warms, so a fall crop usually meets fewer of them. Whatever the season, steady water and feeding keep seedlings growing past light chewing.Feeding is most damaging on seedlings and through spring, and it lets up once the weather warms, so fall sowings meet lighter pressure. Even watering and feeding keep the stand vigorous enough to grow through damage, which shortens the vulnerable window in any season.

  3. Floating row cover

    Cover the seedlings with a row cover, a light fabric sheet, from sowing or transplanting on, because a tiny plant cannot grow fast enough to shrug off heavy chewing.Exclusion from sowing or transplanting protects the stage that is actually at risk. The objective throughout is carrying the crop past the seedling stage, which is the costly one on a crop this quick.

  4. Kaolin clay film

    A kaolin clay coating, a fine white clay dusted over the plants, can cut feeding when there are a lot of beetles. It reduces damage rather than clearing the beetles out, so use it alongside the cover.Kaolin is a repellent barrier for use where pressure is high. Treat it as a supplement to exclusion and timing rather than a replacement for them.

  5. Spinosad

    If beetles are heavy enough to stunt the seedlings, a spinosad spray is an option. Keep the aim on getting plants big enough to handle the damage, spray toward dusk to spare bees, and follow the label.Spinosad supplements exclusion under high pressure. The objective stays establishment past the vulnerable seedling stage rather than a season-long spray program, and applications belong at dusk to limit bee exposure.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Cabbage root maggot
P · 04
Symptoms New transplants and seedlings wilt and grow badly or fall over. If you pull one up, you'll find small white maggots eating the roots. It is worst in cool, wet soil.Plants wilt, grow poorly, and may collapse; pulling a plant reveals small white maggots tunneling in the roots and lower stem. Damage is worst in cool, wet soil at spring establishment. Cause A small fly lays eggs at the base of the plant, and the maggots that hatch burrow down and eat the roots. The fly is most active in cool, damp spring weather.The larvae of the cabbage root fly (Delia radicum) tunnel into brassica roots; the adult lays eggs at the stem base, and the maggots feed below, sometimes killing young plants and opening the door to rots. Organic treatment Once the maggots are in the roots you can't save that plant, so pull and throw away the badly damaged ones. Put your effort into protecting the rest from new eggs.There is no effective rescue once maggots are in the roots; remove and destroy badly affected plants and protect the rest from further egg-laying. Prevention Put a small collar or disk around the base of each transplant to stop the fly from laying eggs there, or use a row cover. Avoid planting into cold, soggy soil, and rotate away from where cabbage-family plants grew.Place a collar or disk around the stem base at transplanting to block egg-laying, or use row cover; avoid planting into cold, wet soil and rotate away from where brassicas grew.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Crop rotation

    Plant kohlrabi where cabbage-family crops have not grown recently. The fly builds up in ground that carried its host plants, so moving the bed puts the new crop away from it.Rotating away from recent brassica ground reduces the carryover population emerging right where the new transplants go in.

  2. Garden sanitation

    Once the maggots are in the roots, that plant cannot be saved, so pull the badly damaged ones and get them out of the garden. Spend the effort instead on keeping the fly from laying more eggs around the plants that are still sound.There is no rescue once larvae are tunneling in the roots and lower stem. Rogue out the wilting and collapsing plants and redirect the effort to blocking further egg-laying on the survivors, since the feeding also opens the way to rots.

  3. Floating row cover

    A row cover, a light fabric sheet laid over the bed, keeps the fly from reaching the plants to lay eggs at their base in the first place. Give it fresh ground to work on: where cabbage-family crops grew last season, the cover can end up holding the emerging flies in rather than out.Exclusion through cool, wet spring establishment covers the period of heaviest adult activity and protects the stage root feeding can kill, the new transplant. Pair it with the rotation above, so the cover is not laid over ground that already carries the pest. In practice that means a bed which grew cabbage-family crops last season, where the cover would hold the emerging flies in with the kohlrabi.

  4. Stem collars

    Set a small collar or disk flat around the base of each transplant. It blocks the fly from laying eggs right against the stem, which is where the maggots start their trip down to the roots.A basal collar or disk placed at transplanting denies the adult its egg-laying site at the stem base. It is the per-plant option where covering the whole bed is impractical.

No spray for this one. Prevention is the control.

Harlequin bug
P · 05
Symptoms Shield-shaped black-and-orange (or black-and-red) bugs on the leaves, which develop white or yellow spots, then brown and look tattered. It is mostly a warm-region problem and loves cabbage-family plants.Shield-shaped bugs up to about 3/8 inch, brightly black-and-yellow or black-and-red, feeding with piercing-sucking mouthparts that leave white stipples; affected leaves brown and look tattered, and heavy feeding wilts plants. A warm-region brassica specialist. Cause The harlequin bug is a colorful stink-bug relative that pierces the leaves and sucks the juices, leaving pale blotches. It strongly prefers cabbage-family plants, especially in the South.The harlequin bug (Murgantia histrionica) is a true bug that specializes on cole crops, most damaging in the southern United States, where it completes several generations a year and overwinters as an adult in debris and weeds. Organic treatment Search out and crush the bugs, their barrel-shaped striped eggs, and the young ones by hand. Use a row cover to keep them off, pull badly infested plants, and clear away weeds and old plants where they hide.Hand-pick and crush adults, nymphs, and the barrel-shaped egg rows; exclude with floating row cover; remove heavily infested plants. Insecticidal soap, pyrethrum, or neem help where pressure is severe. Prevention Clean up garden debris and cabbage-family weeds where the adults overwinter, use row cover, and consider a trap crop of mustard to lure them away, then destroy it.Eliminate overwintering sites by removing crop debris and crucifer weeds, use row cover, and deploy an early trap crop of mustard to divert overwintering adults, then destroy it before the main crop is set out.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Garden sanitation

    Clear away garden debris and cabbage-family weeds at the end of the season, since that is where the adults spend the winter. During the season, pull out any plant that is badly overrun rather than trying to defend it.Adults overwinter in debris and crucifer weeds, so eliminating that shelter is the main preventive lever against a warm-region specialist that completes several generations a year. Roguing heavily infested plants during the season belongs to the same pass.

  2. Trap cropping

    Sow a mustard patch early to lure the overwintered bugs away from the crop, then destroy it before the main planting goes out. Getting the patch out while the bugs are still on it is the step that matters.An early mustard stand pulls overwintered adults off the planting, and this crop's guidance ends the sequence by destroying the stand before the main crop is set out. That removal is not tidying up; it is what stops the concentration becoming a local increase. This method's cautions carry the timing.

  3. Floating row cover

    A row cover, a light fabric sheet, keeps the bugs off the plants. Get it on before they show up rather than after.Exclusion with floating row cover keeps colonizing adults off the crop, and it earns the most early, as overwintered adults move onto the first cabbage-family plants available.

  4. Handpicking

    Search the plants and crush the bugs, the young ones, and the barrel-shaped striped eggs. They are brightly colored and easy to spot on a regular walk through the bed.Hand destruction of adults, nymphs and the barrel-shaped egg rows is practical at garden scale on an insect this conspicuous. Shield-shaped bugs up to about 3/8 inch in black and yellow or black and red are readily found on a scouting pass.

  5. Insecticidal soap

    Where pressure is severe, insecticidal soap sprayed straight onto the bugs can help. It works on the ones it actually wets, so aim at the insects rather than misting the plant.Soap assists under severe pressure and is strictly a contact material, so direct it onto the bugs and their clusters rather than over the foliage in general.

  6. Neem oil

    Neem oil is the other spray named for severe pressure. Coat the bugs directly, and hold off in high heat or when the plants are dry at the roots.Neem is the alternative contact option where pressure is severe. As with soap, coverage of the insects decides the result, and it should be kept off anything in flower nearby, weeds included, where bees forage.

  7. Pyrethrin (botanical)

    Where pressure is severe, pyrethrin, a botanical spray from chrysanthemum flowers, knocks the bugs down on contact and then breaks apart in sunlight within a day or so. Do not let it reach anything in flower; it is in the strictest bee band, which grants no evening window.Pyrethrin supplies contact knockdown under severe pressure and degrades rapidly in sunlight, so it leaves little residue and often needs repeating. Its organic acceptability does not lower the bee precaution: the strictest band applies, so keep spray and drift off bloom, weeds included.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Diseases
Clubroot
D · 01
Symptoms Plants wilt in the afternoon, stay small and yellowish, and don't bounce back. If you dig one up, the roots are swollen into lumpy, club-shaped knobs.Plants wilt in the heat of the day, grow stunted and yellowed, and recover poorly; roots are swollen into distorted clubs and galls instead of normal fine roots, which later rot. Cause A germ that lives in the soil infects the roots of cabbage-family plants and makes them swell, which stops the plant from taking up water and food. It stays in the soil for years.A soilborne organism (Plasmodiophora brassicae) infects brassica roots and forms the galls, which block water and nutrient uptake. It persists in soil for many years, spreads in contaminated soil and water, and is favored by acidic soils below about pH 6.5. Organic treatment There's no cure once a plant has it, so pull and destroy infected plants. Keeping the soil closer to neutral helps hold it back, and growing cabbage-family plants only rarely in that spot starves the germ out.There is no cure once plants are infected; remove and destroy them. Raising soil pH toward neutral with lime suppresses the disease, and long rotations starve it out over time. Prevention Don't grow kohlrabi or other cabbage-family plants in the same spot more than once every few years, longer if you've had clubroot. Keep the soil from being too acidic, improve drainage, and clean soil off your tools.Rotate brassicas out of affected ground on a long cycle (up to 7 years where clubroot is known), keep soil pH up, improve drainage, and avoid moving infested soil on tools and boots.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Crop rotation

    Once clubroot turns up, stop growing kohlrabi and its cabbage-family relatives in that spot for several years. The organism lives on in the soil, and it slowly starves when it has nothing to infect.Resting spores persist in soil for many years. Where clubroot is known, rotate brassicas out on a long cycle, up to 7 years, which draws the soil population down over time.

  2. Raise soil pH (liming)

    Keep the soil from staying acidic by liming it toward neutral. The disease takes hold more readily in acid soil, so this holds it back without curing it. Lime the affected bed rather than the whole garden.Liming toward neutral suppresses the disease, which is favored by soils below about pH 6.5. Confine the treatment to affected ground, since most vegetables prefer soil a little more acid than that, and pair it with the long rotation, as neither clears established ground on its own.

  3. Improve drainage

    Fix the spots where water sits in the bed. The disease travels and infects in wet soil, so better drainage takes away part of what it needs.The pathogen spreads in contaminated soil and water, so correcting drainage on heavy or low ground lowers the infection pressure reaching the roots.

  4. Garden sanitation

    An infected plant cannot be cured, so lift it with the clubbed roots attached and get it out of the garden. Clean the soil off your tools afterward, since the disease rides along on dirt carried from an infested bed.Rogue out infected plants with the galls intact and destroy them; galls left behind add to a soil burden that already lasts years. Clean soil from tools and boots as well, since moving infested soil is one of the ways it reaches clean ground.

No spray for this one. Prevention is the control.

Black rot
D · 02
Symptoms Yellow patches shaped like the letter V appear at the leaf edges, pointing inward, with black veins inside them. It can spread through the plant and rot it.Yellow, V-shaped lesions spread inward from the leaf margins, with the veins inside the V turning black; the disease moves through the vascular system and can blacken and kill the plant. Often the most serious brassica disease in warm, wet weather. Cause A bacteria that often comes in on infected seeds or transplants. It gets into the leaves and travels through the plant's veins, spreading fastest in warm, wet weather.A seedborne bacterium (Xanthomonas campestris pv. campestris) that enters through leaf pores and wounds and moves through the veins; it spreads in warm, wet conditions and on infected seed or transplants. Organic treatment There's no real cure, so remove and destroy infected plants to keep it from spreading. Don't handle or brush against the plants while they're wet.There is no effective cure; remove and destroy infected plants. Avoid working among plants when foliage is wet, since that moves the bacteria. Prevention Begin with clean, certified seed and healthy transplants, don't plant where cabbage-family crops grew recently, space plants for airflow, and avoid overhead watering.Start with clean, certified seed and healthy transplants, rotate 2 to 3 years away from brassicas, give plants room for airflow, and avoid overhead watering and handling wet foliage.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Clean planting stock

    Begin with clean, certified seed and healthy transplants. This one often arrives on the seed or on the young plants themselves, so a clean start is where most of the defense lives.The bacterium is seedborne, so certified seed and healthy transplants close the main entry route. It is a purchase-time decision, settled before anything is in the ground.

  2. Crop rotation

    Do not plant where cabbage-family crops grew recently. Give the ground two to three years before brassicas come back to it.Rotate 2 to 3 years away from brassicas, so inoculum carried in old residues is gone before a susceptible crop returns to that ground.

  3. Airflow and spacing

    Space the plants so air moves between them and the leaves dry off. The disease moves fastest in warm, wet weather, so drying time works against it.Open spacing shortens the warm, wet leaf conditions this bacterium spreads fastest in, and it slows movement from an infected plant to its neighbors.

  4. Water at the base

    Water at the soil instead of over the tops of the plants, so you are not splashing bacteria from leaf to leaf.Basal irrigation removes the overhead wetting and splash that carry the bacterium between plants and lengthen leaf wetness.

  5. Staying out of wet foliage

    Stay out of the bed while the leaves are wet. Brushing past wet plants carries the bacteria from a sick one to a healthy one.Work the planting only when foliage is dry, since handling wet plants moves the bacterium efficiently. This governs when you enter the bed, and it still applies after rain and dew, not only after watering.

  6. Garden sanitation

    There is no real cure, so remove infected plants and get them out of the garden before the disease reaches their neighbors. The yellow V-shaped patches at the leaf edges, with black veins inside them, make it recognizable early.With no effective cure, roguing is the in-season control, so remove and destroy symptomatic plants promptly. The V-shaped marginal lesions with blackened veins allow an early call, before the pathogen has moved far through the vascular system.

No spray for this one. Prevention is the control.

Alternaria leaf spot
D · 03
Symptoms Small, round, dark spots on the leaves, each with a yellow ring and faint target-like circles inside, that grow and run together in wet weather and turn sooty in the center.Small, circular, dark spots with a yellow halo and concentric rings that darken to a sooty center as spores build, enlarging and merging in wet weather. A foliar disease that weakens the plant. Cause Alternaria fungi that can travel on seed and survive on old plant debris, spreading in splashing water and needing wet leaves to take hold. Warm, humid weather brings it on.Alternaria fungi (chiefly Alternaria brassicae), which are seedborne and survive on crop debris, spreading in splashing water and needing leaf wetness to infect; warm, wet weather drives it. Organic treatment Pick off the worst leaves, water at the soil in the morning so leaves dry quickly, and clean up debris. Clean seed and airflow handle most of it; a copper fungicide can help in a wet spell if started early.Remove badly spotted leaves, water at the base in the morning so foliage dries, and clear debris. Clean seed and airflow are the main home levers; a copper fungicide can help in a persistently wet season if started early. Prevention Use clean seed, water at the base instead of overhead, give plants room so the leaves dry, and rotate crucifers and clear debris between plantings.Use clean seed, avoid overhead watering, space for airflow, and rotate crucifers and clear debris that carry the fungi between seasons.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Clean planting stock

    Start with clean seed. These fungi can travel on the seed itself, so a clean packet keeps the disease from arriving with the crop.Alternaria is seedborne, so clean seed shuts one of the two main entry routes. Along with airflow, this is where the home-garden leverage sits.

  2. Crop rotation

    Move kohlrabi and its cabbage-family relatives to a different spot between plantings, since the fungi carry over where those crops grew.The fungi survive on crop debris between seasons, so rotating crucifers out of the bed separates the new crop from the carryover inoculum.

  3. Airflow and spacing

    Give the plants room so air moves through and the leaves dry quickly. The spots need wet leaves to take hold, so drying time does much of the work.Infection requires leaf wetness, so spacing that shortens wet periods works directly against spots establishing, enlarging and running together in wet weather.

  4. Water at the base

    Water at the soil in the morning so any splash dries fast. The disease spreads in splashing water and needs wet leaves to get started.The fungi spread by splash and infect only through wet foliage, so morning irrigation at the base removes the splash route and leaves the day for drying.

  5. Garden sanitation

    Pick off the worst-spotted leaves as you notice them, and clear plant debris between plantings, since that is where the fungi wait for the next crop.Remove badly spotted foliage during the season and clear crop debris between plantings; residue is the principal carryover reservoir.

  6. Copper fungicide

    In a wet spell that will not let up, a copper fungicide can help if you start it early, before the spots are widespread. Keep the spray out of ponds and drains, since copper is very harmful to fish and other water life, and follow the label.Copper earns its place only in a season that stays wet, and only where it goes on early; clean seed and airflow remain the main home levers. It protects new growth rather than curing spotted leaves, it is highly toxic to aquatic life, and it accumulates at the soil surface with repeat use, so keep it away from water, limit how often you lean on it, and follow the label rate.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Downy mildew
D · 04
Symptoms Pale yellow blotches on top of the leaves, with fuzzy grayish growth on the underside, mostly in cool, damp weather. Bad cases discolor the leaves.Pale yellow patches on the upper leaf surface with a fuzzy gray-white growth underneath, mainly in cool, damp weather; severe infection discolors and kills foliage. Kohlrabi's cool, humid season overlaps the weather it likes. Cause A mold-like disease that loves cool, wet, humid weather and spreads through the air and water. Wet leaves and crowded plants make it worse.A fungus-like organism (Hyaloperonospora parasitica) that thrives in cool, wet, humid conditions and spreads by spores in water and air; long leaf wetness and crowded plantings favor it. Organic treatment Open up the airflow so leaves can dry, remove the worst leaves, and use a copper spray if it's spreading. It's hard to stop once the weather stays damp.Improve airflow and let foliage dry, remove badly affected leaves, and apply a copper-based fungicide if pressure is high; the disease is hard to stop once humidity stays high. Prevention Space plants so air moves between them, water at the soil instead of from above, and pick resistant varieties if downy mildew is common where you live.Space plants for good air movement, water at the soil line rather than overhead, and choose resistant varieties where downy mildew is common.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Airflow and spacing

    Space the plants so air moves between them and dries the leaves. This disease wants cool, damp foliage, and kohlrabi grows through that kind of weather.Spacing for air movement shortens the long leaf-wetness periods infection depends on. The crop's cool, humid season overlaps the conditions the pathogen favors, so the layout has to do the drying.

  2. Water at the base

    Water at the soil line rather than over the leaves. Wet foliage and splashing water are how it gets around.Basal irrigation removes the overhead wetting and splash dispersal that extend the wet periods the organism needs.

  3. Resistant varieties

    If downy mildew is common where you live, pick a variety described as resistant when you buy seed.Where downy mildew recurs regionally, a resistant cultivar is the seed-time decision that lowers the pressure the in-season steps have to carry.

  4. Garden sanitation

    Take off the worst-affected leaves, the ones with fuzzy grayish growth underneath, so there is less disease to spread. Once damp weather settles in it is hard to stop, so the preventive steps carry most of the load.Removing badly affected foliage lowers inoculum, but the disease is difficult to arrest once humidity stays high. Treat removal as a supplement to the preventive steps rather than a substitute for them.

  5. Copper fungicide

    If it keeps spreading despite the rest, a copper spray can help. It does more applied early than after the leaves are covered, and keep it away from ponds and drains, since copper is very harmful to fish and other water life.Copper is the escalation when cultural steps are not holding under high pressure. It acts preventively, so it belongs at the first sign rather than in an established outbreak; mind runoff, copper being highly toxic to aquatic life, and limit repeat reliance across seasons.

The bottom rungs are products with label rules: timing, pollinators, and days to wait before harvest. Before you spray →

Blackleg
D · 05
Symptoms Pale, sunken spots dotted with tiny black specks appear on the stem and leaves, and the base of the stem darkens and rots, so the plant may topple. It often arrives on infected seed.Pale, sunken lesions peppered with small black fruiting bodies (pycnidia) on stems and leaves, and a dark, girdling canker at the stem base that can rot the crown and lodge the plant. Cause A fungus that comes in on infected seed or plants and attacks the stem and leaves of cabbage-family crops. It spreads in wet weather and lingers in old plant debris.The fungus Phoma lingam (Leptosphaeria maculans) is chiefly seedborne and survives in brassica debris; it spreads in cool, wet weather by splashing water and infects through wounds and pores. Organic treatment There's no cure, so pull and destroy infected plants. The real fix is prevention: clean seed, rotation, and clearing away old cabbage-family debris.There is no effective cure; remove and destroy infected plants. Management is preventive, since the pathogen is carried on seed and in residue. Prevention Start with clean, certified seed and healthy transplants, rotate away from cabbage-family crops for a few years, and clear away old brassica plants where the fungus survives.Use clean, certified, hot-water-treated seed and disease-free transplants, rotate 3 years away from brassicas, and bury or remove crop debris that carries the fungus over.
The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

  1. Clean planting stock

    Start with clean, certified seed and healthy transplants. This fungus mostly comes into a garden on infected seed or plants, so the packet you buy is the main decision.The fungus is carried chiefly on seed, so the primary control is seed that has been certified and hot-water treated, set out as transplants known to be free of the disease. Management here is preventive by nature, since there is nothing to apply once plants are infected.

  2. Crop rotation

    Keep cabbage-family crops out of the affected spot for a few years, about three. The fungus lingers where those crops grew.Rotate 3 years away from brassicas. The fungus survives in brassica residue, so the interval has to outlast the debris rather than just the season.

  3. Garden sanitation

    There is no cure, so pull and destroy infected plants. Clear away the old cabbage-family debris too, since that is the other place the fungus survives.There is no effective cure once plants are infected, so remove and destroy them, and clear out the brassica residue that carries the fungus over rather than leaving it standing in the bed.

No spray for this one. Prevention is the control.

Verified · 3 sources View
Seasoned
Where to plant next year

Crop rotation

Do not plant kohlrabi or other cabbage-family crops in the same spot year after year. Waiting a few years between them helps avoid soil diseases like clubroot.Rotate so brassicas do not follow brassicas for at least 3 years, and longer where clubroot is known, since the clubroot organism persists in soil for years. Keeping soil pH up also helps suppress it.

Family
Brassica family (Brassicaceae), the cole crops
Years between
3 years
in the same bed
Avoid following
Other cabbage-family crops like cabbage, broccoli, kale, turnips, and radishes.Other brassicas (cabbage, broccoli, cauliflower, kale, Brussels sprouts, collards, turnip, radish), which share clubroot and the cabbage-family pests.
Plant after
Legumes such as beans and peas, or unrelated crops like tomatoes, squash, or onions.
Verified · 2 sources View
In the app · pre-launch

When plant taps you on the shoulder

The plant app sends a timely reminder at every critical moment of your kohlrabi season. The wording adjusts to whichever you pick: beginner or seasoned. Here are three you'll see in Zone 9.

p
plant
Time to harvest your kohlrabi Harvest at tennis-ball size
Your kohlrabi should be about the size of a tennis ball now. Cut the bulb off at the base while it is young and tender, before it gets tough. Your kohlrabi bulb should be about 2 to 3 inches across now. Cut it at the base while it is firm and young, before it turns woody and bitter; standard types do not improve by waiting.
p
plant
Time to feed your kohlrabi Side-dress with nitrogen
Feed your kohlrabi a little nitrogen now to keep it growing steadily. Put the fertilizer near the plants and water it in. Your kohlrabi is established. Side-dress with nitrogen now to keep growth steady and the bulb tender, placing the feed beside the row and watering it in.
p
plant
Hot weather warning for your kohlrabi Heat watch: keep the bulb tender
Hot weather is on the way while your kohlrabi is forming its bulb. Heat can make it woody and bitter. Keep the soil evenly watered, and pick any bulbs that are nearly ready. A hot spell is coming while your kohlrabi is sizing up. Heat above roughly 75°F turns the stem woody and bitter and can trigger bolting. Keep moisture even and harvest promptly if bulbs are near size.
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How we built this guide

Methodology & sources

Every date, temperature, spacing, and recommendation on this page is sourced from university cooperative extension publications, peer-reviewed agricultural research, NOAA climate data, and direct extension calendars. Where claims are softer (traditional gardening wisdom not formally documented), we say so.

Research-backed Documented in cooperative extension publications or peer-reviewed research
Well-grounded A known agronomic principle, but not formally tested for this specific pair
Traditional Time-tested gardening wisdom, limited formal research support
Last reviewed
June 29, 2026
Data version
crops_data_final · v1.0 · schema 2.9
Sources cited on this page
16 publications
Verified entries
Companion-planting claims tagged inline · zone dates verified against 5+ extensions
See all sources cited on this page
  • University of Minnesota Extension umn_ext
  • University of Maryland Extension umd_ext
  • Cornell Cooperative Extension cornell_ext
  • Iowa State University Extension iastate_ext
  • Michigan State University Extension msu_ext
  • NC State Extension ncsu_ext
  • Penn State Extension psu_ext
  • U. of Illinois Urbana-Champaign Extension uiuc_ext
  • UC Davis Postharvest Center ucd_postharvest
  • Texas A&M AgriLife Extension tamu_agrilife
  • Virginia Cooperative Extension 426-331 vce_426_331
  • Piedmont Master Gardeners piedmont_mg
  • UGA Vegetable Garden Calendar uga_calendar
  • Clemson Home & Garden Information Center clemson_hgic
  • UC IPM Statewide IPM Program uc_ipm
  • NOAA 1991-2020 Climate Normals noaa_normals

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Vol. 003 · Kohlrabi · plant.lifestyle