Zone 3 · Brassicas Growing Guide
The alien-looking brassica that deserves far more attention. Crisp, mild, sweet flavour -- eat raw like an apple or cooked. Very fast-maturing and easier than broccoli or cabbage.
In Zone 3, Kohlrabi can be planted outdoors from Apr 15 — the window closes around Aug 24.
Direct sow spring through summer. Multiple successions fit in Zone 3's season.
Zone 3 is split into two subzones. The a/b distinction affects your exact last frost date by 1–2 weeks -- meaningful for heat-sensitive crops and fruit tree hardiness.
| Subzone | Last frost | First fall | Season | Min temp |
|---|---|---|---|---|
| 3a | May 20 | Sep 23 | ~125 days | -40 to -35°F |
| 3b | May 14 | Sep 26 | ~135 days | -35 to -30°F |
plant detects your subzone from your location and adjusts planting windows accordingly.
Here is what to expect at each stage — and what to do when you get there.
Keep soil consistently moist at 60-70°F. Brassicas do not need heat -- they prefer cool germination.
Watch for damping off -- good airflow and not overwatering prevents it. Thin to one plant per cell.
Harden off well before transplanting. Net immediately after planting to protect from cabbage white butterflies -- do not
For cauliflower, tie the outer leaves over the developing curd to blanch it and keep it white. Do this as soon as the cu
Harvest broccoli with a long stem cut -- side shoots will continue producing for weeks. Cauliflower and cabbage are once
Keep harvesting side shoots regularly. A well-managed broccoli plant can produce for weeks after the main head is gone.
At peak: Succession sow every 3 weeks for continuous supply
Kohlrabi is one of the fastest-maturing brassicas and underrated as a vegetable. Sweet and crunchy when harvested young.
Moderate feeder. Consistent balanced feeding produces well-formed bulbs. Avoid excess nitrogen.
Sow every 3 weeks from early spring through early summer, then again in late summer for autumn. Kohlrabi is fast (45-60 days) and must be harvested promptly -- left too long it becomes woody. Spring and autumn sowings work well; skip midsummer plantings in most zones as it bolts in heat. Each sowing gives you a tight 1-2 week harvest window, so small frequent batches beat one big sowing.
Some plants help Kohlrabi thrive. Others compete or cause problems.
Something went wrong? Here is what likely happened and what to do differently next time.
What happened: Established brassicas handle frost well -- it actually sweetens them. But young transplants in their first 2-3 weeks are more vulnerable. A hard freeze can damage or kill recently transplanted seedlings.
Next season: Cover new transplants with fleece for the first 2-3 weeks after planting if frost is possible. Once established they are among the hardiest vegetables you can grow.
What happened: Cabbage white butterflies lay eggs on brassica leaves and the caterpillars can strip a plant in days. This is by far the most common reason brassicas fail. If you did not net, this is almost certainly what happened.
Next season: Net immediately after transplanting -- before you do anything else. Fine mesh netting secured all the way around is the single most important thing you can do for brassicas. Check netting for gaps weekly.
What happened: Brassicas in waterlogged soil develop root problems. Clubroot -- a soil-borne disease -- causes swollen, distorted roots and wilting. Once present in soil it persists for many years.
Next season: Improve drainage before planting. If clubroot is suspected, rotate brassicas to a new bed and do not grow them in the affected soil for 4-5 years. Liming to raise soil pH above 7 discourages clubroot.
What happened: Brassicas need consistent moisture to develop good heads. Drought stress causes premature flowering in broccoli and cauliflower, and split heads in cabbage.
Next season: Water consistently and mulch around plants to retain moisture. A dry spell during head formation is the most damaging period.
What happened: Cauliflower is the most demanding -- it needs consistent temperatures and care to form a good curd. Broccoli heads opening into yellow flowers usually means the temperature swung too warm. Both benefit from 6+ hours of sun.
Next season: Cauliflower in particular needs a consistent, cool growing environment. Autumn sowings often perform better than spring ones in warmer zones. Shade cloth can help in warm spells.
Something didn't work out? Here is what likely happened and what to do differently next season.
What happened: Established brassicas handle frost well -- it actually sweetens them. But young transplants in their first 2-3 weeks are more vulnerable. A hard freeze can damage or kill recently transplanted seedlings.
Next season: Cover new transplants with fleece for the first 2-3 weeks after planting if frost is possible. Once established they are among the hardiest vegetables you can grow.
What happened: Cabbage white butterflies lay eggs on brassica leaves and the caterpillars can strip a plant in days. This is by far the most common reason brassicas fail. If you did not net, this is almost certainly what happened.
Next season: Net immediately after transplanting -- before you do anything else. Fine mesh netting secured all the way around is the single most important thing you can do for brassicas. Check netting for gaps weekly.
What happened: Brassicas in waterlogged soil develop root problems. Clubroot -- a soil-borne disease -- causes swollen, distorted roots and wilting. Once present in soil it persists for many years.
Next season: Improve drainage before planting. If clubroot is suspected, rotate brassicas to a new bed and do not grow them in the affected soil for 4-5 years. Liming to raise soil pH above 7 discourages clubroot.
What happened: Brassicas need consistent moisture to develop good heads. Drought stress causes premature flowering in broccoli and cauliflower, and split heads in cabbage.
Next season: Water consistently and mulch around plants to retain moisture. A dry spell during head formation is the most damaging period.
What happened: Cauliflower is the most demanding -- it needs consistent temperatures and care to form a good curd. Broccoli heads opening into yellow flowers usually means the temperature swung too warm. Both benefit from 6+ hours of sun.
Next season: Cauliflower in particular needs a consistent, cool growing environment. Autumn sowings often perform better than spring ones in warmer zones. Shade cloth can help in warm spells.
Know what to look for before it gets out of hand — early identification is the most important step.
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plant uses your ZIP code and real frost data to tell you the right day — not just the right month. Get notified when your planting window opens, when to succession sow, and when to cut back for next season.
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plant monitors these conditions and sends an alert the moment they are forecast for your location.
Traditional growers have used lunar cycles to time planting and harvest for centuries. The moon affects moisture levels in soil and sap flow in plants.
These guides get better when growers share what they know. If something's off or you've learned something worth passing on, add it here -- accepted tips earn you a Founding Grower badge when plant launches.
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