Feeding and fertilizer: what the numbers mean -- plant

The three numbers

N, P, K: what each one feeds.

A tomato plant from leaves to roots, showing where each nutrient does its work

Feeds Leaves and green growth

Nitrogen is the leaf and stem builder. It makes plants grow lush, green, and fast, which is exactly what you want from salad greens and anything you grow for its leaves.Nitrogen drives vegetative growth: it is the backbone of chlorophyll and protein, so it powers leaves, stems, and deep green color. Leafy crops want the most of it.

Sign you're short

Short on nitrogen, the oldest leaves at the bottom turn yellow first and growth slows, because the plant moves what little it has to its newest leaves.Deficiency shows first in the oldest, lowest leaves, which yellow and fade as the plant moves nitrogen up to new growth; overall growth stalls.

Feeds Roots, flowers, and fruit set

Phosphorus is the root and flower builder. It helps young plants get established and helps them set flowers and fruit.Phosphorus fuels energy transfer, so it builds strong roots and powers flowering and fruit set. It matters most at establishment and at bloom.

Sign you're short

Short on phosphorus, plants grow slowly and stay small, often with a dull or purple tinge to the leaves, and they flower poorly.Deficiency reads as stunted, sluggish growth with a dull, often purple cast to leaves and stems, and poor flowering.

Feeds Fruit and overall vigor

Potassium is the whole-plant health nutrient. It helps plants handle stress, shrug off disease, and ripen good fruit.Potassium runs the plant's plumbing and regulation: water movement, disease and drought tolerance, and fruit quality. It is the all-around vigor nutrient.

Sign you're short

Short on potassium, the edges of the leaves turn brown and scorched, stems go weak, and the fruit is poor.Deficiency appears as scorched, browning leaf margins, usually on older leaves, with weak stems and poor, low-quality fruit.

Those three numbers on the bag are always nitrogen, then phosphorus, then potassium, written as a percentage. A balanced one like 10-10-10 works for most crops. A bigger first number feeds leaves; a bigger last number feeds fruit. Pick the ratio that matches what you want from the plant.The three numbers on any fertilizer are the percentage by weight of nitrogen, phosphorus, and potassium, always in that order. A balanced feed like 10-10-10 covers most crops; a higher first number pushes leafy growth, a higher last number favors fruit. Match the ratio to what you are growing for.

Feeding by crop

What each crop wants.

Alliums

Garlic 21-0-0 Nitrogen-forward Side-dress in spring

Leek 10-10-10 Balanced base, nitrogen-forward Side-dress once or twice during the long season

Onion Nitrogen-forward Side-dress periodically

Shallot Nitrogen-forward Side-dress twice early

Spring Onion / Scallion 10-10-10 Balanced, moderate nitrogen Light feeding during leaf growth

Beans & Peas

Broad Beans / Fava 5-10-10 Balanced pre-plant, little to no nitrogen low

Dry Beans 5-10-10 Balanced pre-plant, light nitrogen sidedress low

Edamame 5-10-10 Balanced pre-plant, soybean inoculant, little to no nitrogen low

Green Beans (Bush) 5-10-10 Balanced pre-plant, light nitrogen sidedress low

Pole Beans 5-10-10 Balanced pre-plant, light nitrogen sidedress low

Snow Peas 5-10-10 Balanced pre-plant, little to no nitrogen low

Sugar Snap Peas 5-10-10 Balanced pre-plant, little to no nitrogen low

Berries & Shrubs

Blackberry 10-10-10 Balanced, nitrogen-forward in spring Once or twice per year

Blueberry Complete, acidifying Twice per year

Elderberry 10-10-10 Balanced, with nitrogen Once per year

Raspberry 10-10-10 Balanced, nitrogen-forward in spring Once or twice per year

Brassicas

Broccoli 21-0-0 Nitrogen-rich fertilizer twice a season

Brussels Sprouts 21-0-0 Nitrogen-rich fertilizer every 3 to 4 weeks

Cabbage 10-10-10 Nitrogen-rich fertilizer once or twice during the season

Cauliflower 10-10-10 Nitrogen-rich fertilizer once or twice during the season

Kohlrabi 10-10-10 Balanced, then nitrogen twice a season

Citrus

Grapefruit 2-1-1 Citrus (nitrogen-forward, with iron, zinc, and manganese) split applications through the growing season

Lemon Citrus (nitrogen-forward) light doses several times through the growing season

Lime Citrus (nitrogen-forward) light, frequent doses through the growing season

Mandarin (Clementine) 2-1-1 Citrus (nitrogen-forward, with iron, zinc, and manganese) split applications through the growing season

Orange (Navel) 2-1-1 Citrus (nitrogen-forward, with iron, zinc, and manganese) split applications through the growing season

Companion & Pollinator

Bee Balm 10-10-10 Balanced, all-purpose light

Borage 10-10-10 Balanced or low-nitrogen light

Calendula 10-10-10 Balanced or low-nitrogen light

Chamomile 10-10-10 Low-nitrogen or none minimal

Cosmos 5-10-10 None to very low; usually unnecessary rarely

Echinacea (Purple Coneflower) 12-6-6 Balanced, low-nitrogen slow-release Low

Marigold 10-10-10 Balanced or low-nitrogen light

Sweet Alyssum 5-10-5 Balanced, low-nitrogen light

Sweet Pea Balanced, then bloom-oriented (moderate, avoid excess nitrogen) monthly

Zinnia 10-10-10 Balanced or low-nitrogen light

Corn

Field Corn Nitrogen-forward, sidedressed high

Flint Corn Nitrogen-forward, sidedressed high

Popcorn Nitrogen-forward, sidedressed high

Sweet Corn Nitrogen-forward, sidedressed high

Cucumbers

Cucumber 10-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

English Cucumber 10-10-10 Balanced at planting, then regular feeding high in nitrogen and potassium At planting, then feed steadily through the season

Pickling Cucumber 10-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Slicing Cucumber 5-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Edible & Harvest

Lavender None to minimal rarely

Nasturtium None to low-nitrogen rarely

Sunflower 10-10-10 Balanced moderate

Viola 5-10-10 Balanced or low-nitrogen light

Fig & Subtropical

Fig 10-10-10 Balanced granular (e.g. 10-10-10) 2-3x per year, spring to midsummer

Persimmon 10-10-10 Balanced granular (e.g. 10-10-10) 1-3x per year

Pomegranate 10-10-10 Balanced granular (e.g. 10-10-10) 1-2x per year

Fruit

Strawberry 16-16-16 Balanced granular At planting and through the first season for new plantings; for established June-bearing beds, once a year at renovation.

Fruiting Veg

Eggplant / Aubergine 10-10-10 Balanced at planting, then nitrogen at fruit set At planting, then side-dress at fruit set

Okra 10-10-10 Balanced at planting, then a light side-dress once pods begin At planting, then side-dress after first pods

Tomatillo 10-10-10 Balanced vegetable fertilizer every 4 weeks

Herbs

Basil 5-10-5 Balanced or slightly nitrogen-forward liquid every 3-4 weeks

Chives 5-10-5 Balanced or low-nitrogen fertilizer light, once or twice per season

Cilantro / Coriander 21-0-0 Nitrogen-rich fertilizer once or twice per crop

Dill Light balanced feeding once per crop, or none

Lemongrass Nitrogen-forward soluble every 1-2 weeks

Mint 16-16-16 Balanced granular fertilizer Once or twice per season

Oregano None to minimal rarely

Parsley 5-10-5 Balanced vegetable fertilizer once or twice per season

Rosemary None to minimal rarely

Sage None to minimal rarely

Thyme None to minimal rarely

Leafy Greens

Arugula 21-0-0 Nitrogen-rich fertilizer once or twice per crop

Bok Choy 10-10-10 Nitrogen-rich fertilizer once or twice per crop

Celery 10-10-10 Nitrogen-rich balanced high

Collards (Collard Greens) 10-10-10 Nitrogen-rich fertilizer every 3 to 4 weeks

Kale 21-0-0 Nitrogen-rich fertilizer every 4 to 6 weeks

Lettuce (Leaf) 10-5-5 Nitrogen-rich fertilizer every 3 weeks

Spinach 21-0-0 Nitrogen-rich fertilizer once or twice per crop

Swiss Chard 21-0-0 Nitrogen-rich fertilizer at planting, then side-dress through the long harvest

Melons

Cantaloupe / Rockmelon 5-10-10 Lower-nitrogen at planting, then nitrogen side-dress At planting, then side-dress before vines run and again after fruit set

Honeydew Melon 5-10-10 Lower-nitrogen at planting, then nitrogen side-dress At planting, then side-dress once or twice

Watermelon 5-10-10 Lower-nitrogen at planting, then nitrogen side-dress At planting, then side-dress once or twice

Native & Specialty

Mulberry 10-10-10 Balanced granular (e.g. 10-10-10), sparingly 0-1x per year

Pawpaw 10-10-10 Balanced granular (e.g. 10-10-10) 2-4x in the first half of the season while young; 1x per year once established

Peppers

Banana Pepper 10-10-10 Balanced at planting, then calcium nitrate at fruit set At planting, then side-dress after fruit set

Bell Pepper 5-10-10 Balanced at planting, then calcium nitrate at fruit set At planting, then side-dress after fruit set

Cayenne Pepper 10-10-10 Balanced at planting, then a light nitrogen side-dress at fruit set At planting, then side-dress after fruit set

Habanero Pepper 10-10-10 Balanced at planting, then a light nitrogen side-dress at fruit set At planting, then side-dress after fruit set

Jalapeño 5-10-10 Balanced or low-nitrogen at planting, then nitrogen at fruit set At planting per soil test, then side-dress after fruit set

Pome Fruit

Apple 10-10-10 Balanced annual

Pear (Asian) 10-10-10 Balanced annual

Pear (European) 10-10-10 Balanced annual

Root Vegetables

Beet 10-10-10 Balanced low

Carrot 5-10-10 Balanced low-nitrogen low

Parsnip 5-10-10 Balanced low

Potato 10-10-10 Balanced, moderate nitrogen Moderate

Radish 5-10-10 Balanced low-nitrogen low

Sweet Potato 5-10-10 Low nitrogen, higher potassium Low

Turnip 10-10-10 Balanced low

Squash

Acorn Squash 10-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Butternut Squash 10-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Pumpkin 13-13-13 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Spaghetti Squash 10-10-10 Balanced at planting, then nitrogen side-dress At planting, then side-dress once or twice

Yellow Summer Squash 10-10-10 Balanced At planting, then one side-dressing

Zucchini / Courgette 10-10-10 Balanced At planting, then one side-dressing

Stone Fruit

Apricot 10-10-10 Balanced granular (e.g. 10-10-10) 1x per year

Cherry (Sour) 10-10-10 Balanced granular (e.g. 10-10-10) 1x per year

Cherry (Sweet) 10-10-10 Balanced granular (e.g. 10-10-10) 1x per year

Nectarine 10-10-10 Balanced granular (e.g. 10-10-10) 1-2x per year

Peach 10-10-10 Balanced granular (e.g. 10-10-10) 1-2x per year

Plum 10-10-10 Balanced granular (e.g. 10-10-10) 1-2x per year

Tomatoes

Beefsteak Tomato 5-10-10 Tomato fertilizer every 2 weeks

Cherry Tomato 5-10-10 Tomato fertilizer every 2 weeks

Grape Tomato 5-10-10 Tomato fertilizer every 2 weeks

Heirloom Tomato 5-10-10 Tomato fertilizer every 2 weeks

Roma Tomato 5-10-10 Tomato fertilizer every 2 weeks

These are the crops with verified growing guides. We add each crop's feeding as its guide is checked against university extension sources, so the list keeps growing.

FAQ

Common questions

They are the percentage by weight of three nutrients, always in the same order: nitrogen, phosphorus, and potassium (N-P-K). So 10-10-10 is 10 percent of each, a balanced feed; 5-10-10 is lower in nitrogen. A higher first number pushes leafy growth, a higher last number favors fruit.

Nitrogen, phosphorus, and potassium, the three nutrients plants need in the largest amounts. Nitrogen builds leaves and green growth, phosphorus builds roots and powers flowering and fruit set, and potassium drives fruit quality and overall vigor.

It depends on the crop and your soil. Heavy feeders like tomatoes often want feeding every couple of weeks once they set fruit, leafy greens roughly every few weeks, and light feeders like carrots little or none. Feed at planting, then through the season at the crop’s pace, and always water it in.

Usually too much nitrogen. Nitrogen drives leafy growth, so an excess gives lush green plants that never settle into flowering and fruiting. Switch to a feed with a lower first number and a higher last number (more potassium), and ease off the nitrogen.

Organic fertilizers like compost and manure release slowly and build healthy soil over time. Synthetic fertilizers act fast and give precise nutrient numbers but do not improve the soil itself. Both grow good food; many gardeners use compost as a base and add a targeted fertilizer when a crop needs a boost.

Less, but usually still some. Rich, compost-fed soil carries light and moderate feeders a long way. Hungry, fruiting crops like tomatoes and peppers still benefit from feeding through the season. A soil test from your extension office is the only way to know what your soil actually needs.

What the three numbers mean.

N, P, K: what each one feeds.

Feed steadily, and go easy.

What each crop wants.

Common questions

Backed by university extensions

Growing notes, weekly.