Kale

Choosing & planning

What is kale and where does it grow best?

Kale (Brassica oleracea var. acephala) is a cool-season leafy green in the cabbage family that produces maximum yields in early spring or fall. It grows best in full sun to part shade with fertile, well-drained soil and temperatures between 55–75°F (13–24°C). It is one of the hardiest vegetables available and can be grown across a very wide range of climates.

What are the main types of kale, and how do they differ?

The main types are curly kale (frilly, ruffled leaves, robust flavor), Lacinato/dinosaur kale (long, puckered dark-green strap leaves, heat- and cold-tolerant), Red Russian (flat oak-leaf shape with purple veins, most tender), and Siberian kale (broad, flat, blue-green leaves, very cold-hardy). A further botanical distinction separates Brassica napus kales (Russo-Siberian types such as Red Russian and Siberian, with more tender leaves, better flavor, and stronger cold hardiness) from Brassica oleracea European curly types.

Which kale varieties are recommended, and how do I choose one?

Reliable varieties include Red Russian (50 days, tender flat leaves), Improved Dwarf Siberian (50 days, cold-tolerant frilly leaves), Starbor (55 days, green curly), Redbor hybrid (55 days, burgundy-red frilly leaves), and Toscano/Lacinato (65 days, heat- and cold-tolerant). Choose cold-hardy types such as Siberian or Red Russian for fall harvests; Lacinato and Siberian show the most resilience in warmer climates. Days-to-maturity on seed packets reflect direct-seeded crops; subtract about 14 days if transplanting.

What should I look for when buying kale seeds or transplants?

Choose transplants with dark-colored leaves and 4–6 mature leaves with a well-developed root system; avoid yellow or brown leaves. When buying seed, look for lots that have been tested negative for black rot and black leg.

Can I grow kale in my climate or hardiness zone?

Kale grows across Zones 3–11. In Zones 3–4, start seeds indoors 4–6 weeks before the last frost; in Zones 5–6, it excels in spring and fall; in Zone 8 and above, grow it as a fall-through-winter crop and protect from summer heat with shade cloth. Young plants tolerate temperatures down to 25°F and mature plants can handle even colder conditions.

Can I grow kale in containers or pots, and what size do they need?

Yes, kale grows well in containers. A single plant needs at least a 5-gallon pot or a container at least 12 inches in diameter and depth. Fabric pots in the 5–10-gallon range are particularly effective because they provide aeration, drainage, and portability.

Can I grow kale indoors or in a greenhouse?

Yes — seedlings can be grown entirely indoors under adequate light and harvested with scissors. Established plants can also overwinter in a cold frame, hoophouse, or greenhouse to extend the harvest season.

Starting from seed & propagation

Should I start kale from seed or buy transplants?

Both work well. Direct seeding is common for baby-leaf harvests, and seeds are inexpensive and germinate rapidly. Transplants provide an earlier full-size harvest and are preferred for fall crops when timing is tight; transplant-grown kale matures about 14 days sooner than direct-seeded crops.

When should I start kale seeds indoors?

Start seeds indoors 3–6 weeks before the planned outdoor transplant date, which is typically 4–5 weeks before the last spring frost. For a fall crop, start seeds indoors in May and transplant to the garden in June–July.

How deep should I sow kale seeds?

Sow kale seeds ¼ to ½ inch deep.

What temperature do kale seeds need to germinate?

Johnny’s Seeds recommends keeping soil temperature above 75°F (24°C) until germination, then reducing air temperature to about 60°F (16°C) for growing on. Seeds can also germinate in cooler soil around 45°F, making kale adaptable to a range of early-season conditions.

How long do kale seeds take to germinate?

Kale seeds typically germinate in 7–10 days.

Why are my kale seedlings leggy or weak?

Insufficient light is the primary cause. Kale receiving only 4–5 hours of sunlight will become leggier and produce fewer, smaller leaves. Provide at least 6–8 hours of direct light for strong, compact seedlings.

Site, soil & timing

How much sun does kale need?

Kale grows best with 6–8 hours of direct sunlight per day. It tolerates partial shade (4–5 hours) but will be leggier with smaller, fewer leaves. In hot climates, afternoon shade helps prevent leaf scorch.

What type of soil does kale prefer?

Kale prefers fertile, well-drained soil rich in organic matter. Loose soil encourages a more extensive root system, improving water and nutrient uptake; rocky or compacted soils limit growth.

What soil pH does kale need?

Kale grows best at a soil pH of 6.0–7.5, with 6.5–6.8 ideal to discourage clubroot disease. It can tolerate slightly alkaline conditions.

How should I prepare and amend the soil for kale?

Till at least 10 inches deep, remove weeds and rocks, and incorporate a 1–2-inch layer of compost at least 7 days before planting. Work fertilizer into the top 6 inches based on soil test results; compost applications should not exceed 1 inch per 100 square feet.

When should I plant kale outdoors?

For spring planting, set transplants out 3–5 weeks before the last frost date. For fall planting, sow or transplant 6–8 weeks before the first expected frost. In mild-winter zones 8–10, planting can continue throughout fall.

Does kale tolerate frost, heat, or drought?

Kale is cold-tolerant to about -6°C (21°F), with young plants surviving temperatures down to 25°F; mature plants tolerate even harder freezes, and flavor improves noticeably after frost. High summer temperatures above 75°F reduce growth and cause bitter flavors. Kale can tolerate short-term drought, but leaf quality and flavor suffer with inconsistent moisture.

Planting

How far apart should I space kale plants?

Space plants 12–18 inches apart in the row; 18–24 inches is recommended for larger transplants. Thin direct-seeded plants to 9–12 inches apart once seedlings reach 2–3 inches tall.

How far apart should the rows be?

Rows should be 18–36 inches apart, with 2 feet being a common practical minimum.

How deep should I plant kale?

Sow seeds ¼–½ inch deep. Set transplants at the same depth they were growing in their pot.

Are there special planting techniques for kale?

Raised beds work particularly well because the soil warms faster, allowing earlier planting. Starting seedlings in flats or greenhouse cells and transplanting gives kale a head start over weeds and is preferred for fall crops.

What grows well next to kale (companion plants)?

Garlic, onions, chives, and leeks mask kale’s scent from aphids; dill and sweet alyssum attract aphid-parasitoid wasps; thyme and sage reduce diamondback moth; nasturtiums act as a trap crop for aphids and caterpillars; hairy vetch as a cover crop has been shown to double kale yield. Beets, celery, cucumber, herbs, and spinach are also noted as friendly neighbors.

What should I avoid planting near kale?

Avoid sunflowers (sesquiterpene lactones inhibit brassica germination), fennel (allelopathic to most crops within 3–5 feet), other brassicas (concentrate pest pressure), strawberries, and tomatoes.

Watering

How much and how often should I water kale?

Kale needs about 1–1.5 inches of water per week. Water deeply and infrequently to maintain even soil moisture rather than giving frequent shallow waterings.

What is the best way to water kale?

Water deeply and infrequently; drip irrigation is preferred to conserve water and keep foliage dry. After harvesting leaves, ensure adequate moisture to support the rapid production of new growth.

What are the signs of over- or under-watering kale?

Moisture fluctuations — whether too much or too little — cause leaves to become tough and develop off-flavors. Consistent, even moisture is essential for the highest-quality, most tender and flavorful leaves.

Should I mulch kale, and with what?

Yes — apply a 2–3-inch layer of organic mulch such as straw around plants to conserve moisture, keep soil cool, and suppress weeds. Straw mulch also helps plants survive winter; ensure it comes from a herbicide-free source.

Feeding & fertilizing

How should I fertilize kale?

Incorporate a complete N-P-K fertilizer into the soil before planting, then side-dress with a nitrogen-based fertilizer (such as 21-0-0 at ½ cup per 10 feet of row) about 4 weeks after transplanting. Place granular fertilizer 6 inches to the side of the plants and water it in.

What fertilizer or nutrients does kale need?

Kale needs the most nitrogen for leaf color, tenderness, and tissue growth; phosphorus for root development; and potassium for water and nutrient movement. A complete fertilizer (such as 10-10-10 or 20-10-20) with nitrogen as the highest number, supplemented with compost, meets these needs.

When and how often should I feed kale?

Apply a base fertilizer before planting, then side-dress with nitrogen about 4 weeks after transplanting or thinning. Continue feeding with compost monthly or with a liquid fertilizer every third watering, or with a nitrogen-rich fertilizer every 4–6 weeks throughout the growing season.

What are the signs of nutrient deficiency in kale?

Yellowing of older, lower leaves progressing upward signals nitrogen deficiency; correct by side-dressing with blood meal or a balanced fertilizer. Yellowing or distortion of leaves can also indicate calcium deficiency.

Support, training & pruning

Does kale need staking, caging, or a trellis?

Kale generally does not need a trellis or cage — it is a sturdy, self-supporting plant. In windy locations or for very tall varieties (which can reach 6–7 feet), staking with bamboo canes or encircling plants with twine may prevent flopping.

How do I support kale as it grows?

For standard varieties no support is needed. For tall plants in windy sites, insert bamboo canes and tie the stems, or encircle a group of plants with twine. Mulching the base also helps stabilize plants.

Should I prune, train, or remove suckers from kale?

Kale responds well to the cut-and-come-again approach: regularly removing the oldest, outermost lower leaves redirects energy to new growth from the center and delays bolting. You can also prune the growing tip to trigger side-shoot sprouting from stem nodes, though this tends to reduce overall yield. Never remove more than one-third of the foliage at once, and always preserve the central growing tip for continuous upward growth.

Pollination & fruit set

Does kale need pollinators, or is it self-pollinating?

Kale flowers are not self-fertilizing; cross-pollination is needed to produce seeds. For seed saving, plant at least 10 plants close together to ensure good pollination. Kale is a biennial that only flowers in its second year after experiencing a cold period.

Pests

What pests commonly attack kale?

The main pests are cabbage aphids (gray-green, waxy, clustered on new growth), imported cabbageworm, cabbage looper, and diamondback moth caterpillars (causing ragged holes), and crucifer flea beetles (tiny shot-holes, worst on seedlings). Cutworms can sever seedlings cleanly at soil level overnight.

How do I identify kale pest damage?

Gray-green powdery clusters on leaves and stems indicate cabbage aphids. Large ragged holes with a green caterpillar and frass visible point to imported cabbageworm. Tiny round shot-holes especially on seedlings are caused by flea beetles. Seedlings cut cleanly at soil level overnight indicate cutworms.

How do I prevent kale pests?

Apply row covers or insect netting at transplant time to physically exclude flying pests — hardware cloth does not exclude most insects. Companion planting with garlic, dill, sweet alyssum, and nasturtiums can reduce pest pressure by masking the plant’s chemical signals and attracting parasitoid wasps.

How do I control kale pests organically and chemically?

Spray insecticidal soap or neem oil on cabbage aphids (plain water is ineffective due to their waxy coating; check first for tan mummy aphids and wait 3–5 days if present, as parasitoid wasps may collapse the colony naturally). Apply Bacillus thuringiensis (Bt/BTK) to control cabbageworms and loopers while larvae are small. Use cardboard collars at planting to protect against cutworms. For flea beetles, row covers are the first defense; only treat if more than 2–5 beetles per plant are present on young transplants.

Diseases

What diseases commonly affect kale?

The most common diseases are downy mildew, black rot (Xanthomonas campestris), clubroot, and black leg (Phoma lingam).

How do I recognize kale disease symptoms?

Downy mildew shows as angular yellow patches on the upper leaf surface with gray fuzzy growth on the underside. Black rot produces V-shaped yellow lesions at leaf margins with black veins. Clubroot causes stunted, wilting plants with swollen, club-shaped roots.

How do I prevent kale diseases?

Use long crop rotations with non-brassica crops (3–7 years depending on the disease), start with clean seed mixes and sanitary practices, and maintain soil pH at 6.5–6.8 (or raise to 7.2+ to suppress clubroot). Buy seed lots tested negative for black rot and black leg.

How do I treat or manage kale diseases?

For black rot, remove infected plants immediately and rotate away from brassicas for 3–4 years. For clubroot, lime the soil to pH 7.2 or above and rotate for 5–7 years. For downy mildew, improve air circulation and apply copper spray if needed.

Disorders & troubleshooting

What physiological disorders affect kale (such as blossom-end rot, cracking, or sunscald)?

Bolting — sending up a tall flower stalk — is the primary physiological disorder, triggered by high temperatures or long days; it causes bitter leaves and diverts energy away from leaf production.

What causes these disorders and how do I prevent them?

Bolting is triggered by high temperatures and long days; growing kale in the cool seasons of spring and fall prevents it. Once kale bolts, harvest the remaining leaves promptly; the flower buds can be cooked and eaten like broccoli.

Why are my kale leaves yellowing, curling, or spotted?

Yellowing of older, lower leaves progressing upward indicates nitrogen deficiency; correct by side-dressing with blood meal or balanced fertilizer. Yellowing or distortion can also signal calcium deficiency. Angular yellow patches with gray fuzz underneath indicate downy mildew; V-shaped yellow lesions at leaf margins with black veins indicate black rot.

Why is my kale not growing or producing well?

High summer temperatures above 75°F reduce growth and cause bitter flavors. Insufficient sunlight (under 6 hours) results in weak, pale plants with few leaves. Moisture or fertilizer stress during growth also limits leaf quality and yield.

Harvest

How long does kale take to mature?

Baby greens are ready 20–30 days after seeding. Most kale varieties reach full maturity in 50–75 days from direct seeding; subtract about 14 days if growing from transplants.

How do I know when kale is ready to harvest?

Begin harvesting once the plant is 8–12 inches tall and the outermost leaves are roughly the size of your palm. For sweeter flavor, wait until after the first frost.

How do I harvest kale correctly?

Select the largest, most mature leaves from the bottom and outside of the plant first, cutting close to the main stem with clean sharp pruning shears or by gripping the leaf at the base and twisting it off. Always preserve the central growing tip (top 4–6 leaves) and never remove more than one-third of the foliage at once so the plant continues producing.

How often should I harvest kale?

Return to plants every 5–7 days for consistent, continuous leaf production; this regular removal of mature leaves stimulates the plant to generate new growth.

Storage, preservation & seed saving

How should I store fresh kale, and how long does it keep?

Wrap leaves in paper towels, place in a zip-top bag, and refrigerate in the coldest part of the fridge. Fresh kale keeps 3–5 days per one source; another recommends using it within one week. Wait to wash leaves until ready to use to prevent mold.

How can I preserve kale (canning, freezing, or drying)?

Kale can be frozen raw — de-stem, chop, dry off excess moisture, and seal in freezer bags — or blanched in boiling water for 2 minutes, then cooled, drained, and packaged with ½ inch headspace before freezing. Kale can also be dried in a food dehydrator and crumbled or ground into powder for use in smoothies, soups, and sauces.

How do I save seeds from kale for next year?

Kale is biennial and flowers in its second year after a cold period; it is not self-fertilizing, so plant at least 10 plants close together for good pollination. Let seed pods dry naturally on the plant until light brown, then rub them over a bowl to release seeds. Air-dry seeds for one week before storing in a dry, dark container; properly stored seeds remain viable for up to 4 years.

Uses & nutrition

What is kale commonly used for in cooking?

Kale can be steamed, sautéed, stir-fried, or substituted for spinach in omelets, casseroles, and quesadillas. Tender young leaves work well raw in salads; larger leaves are best cooked. Kale is also popular in smoothies, juices, soups, and baked as kale chips.

What are the nutritional benefits of kale?

Kale is exceptionally nutrient-dense: one serving provides about 200% of the daily vitamin C requirement and contains vitamins A, K, B6, manganese, calcium, copper, potassium, and magnesium. It is rich in antioxidants, can help lower cholesterol to reduce heart-disease risk, and contains cancer-fighting compounds including indole-3-carbinol, which appears to boost DNA repair and block cancer-cell growth.

Season extension & regional growing

How can I extend the kale growing season?

Apply row covers to extend the harvest period into colder months. Plants can be grown in cold frames or hoophouses to harvest through winter. Mature plants left in the garden can supply greens through winter in many regions.

Can I grow a fall or second crop of kale?

Yes — plant 6–8 weeks before the first fall frost for an autumn and early-winter harvest. For fall crops, start seedlings indoors in May and transplant in June–July. In Zones 8–10, planting can continue throughout fall for a winter harvest.

How do I grow kale in a particularly hot or cold region?

In hot regions (Zone 8+), grow kale as a fall-through-winter crop; use shade cloth and plant in afternoon shade to protect from summer heat, as kale can bolt quickly during heat waves. In cold regions (Zones 3–4), start seeds indoors 4–6 weeks before the last frost and use row covers or cold frames to extend the season; mature plants survive very cold temperatures and can be left in the garden all winter.