Growing Kale: Variety Guide, Timing & Harvest Tips

title: "Growing Kale: Complete Garden Guide"

—- title: "Growing Kale: Complete Garden Guide" slug: growing-kale hub: vegetables category: Vegetable description: "How to grow kale from seed or transplant: variety selection, timing, spacing, continuous harvest technique, and managing caterpillar pests and aphids." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

I don't grow kale at my Long Island plot — the beds are committed elsewhere. This guide is sourced from Cornell Cooperative Extension, Penn State Extension, NC State Extension, and UMass Extension, which collectively offer the most thorough published guidance on home kale production in the Northeast and mid-Atlantic.

Kale is among the hardiest, most cold-tolerant vegetables available to home gardeners. It is technically a biennial, and in zones 6—9 a fall-planted kale will often overwinter successfully and resume growth in spring before going to seed. Flavor improves substantially with cold temperatures — the standard advice that \"kale tastes better after a frost\" is grounded in real biochemistry: frost converts starches to sugars in the leaves.

Variety selection

Brassica oleracea var. acephala encompasses kale and collard greens. Major kale types:

Curly kale: 'Dwarf Siberian' (50 days), 'Winterbor' (60 days), 'Redbor' (60 days, purple). Per Cornell Cooperative Extension, curly types are the most widely available and cold-hardy. 'Winterbor' is among the most cold-tolerant varieties available per Penn State Extension.

Lacinato/Dinosaur kale (B. oleracea var. acephala, Nero di Toscana group): 'Lacinato' (62 days), 'Black Magic' (57 days). Long, narrow, dark blue-green leaves with puckered texture. Milder flavor than curly types. Per NC State Extension, lacinato types are popular in markets and restaurants; excellent for year-round production.

Red Russian kale: 'Red Russian' (50 days). Flatter leaves, purple stems, very tender texture suited to salads. Per Johnny's Selected Seeds, Red Russian is the mildest-flavored kale type — preferred for raw applications. Less cold-hardy than curly types.

Kalette (kale sprouts): A hybrid of kale and Brussels sprouts producing small edible rosettes on the stem. Relatively new category; 'Kalettes Mix' available from specialty seed suppliers.

Days to maturity: 50 days ('Dwarf Siberian', 'Red Russian') to 62 days ('Lacinato').

USDA zones and temperature requirements

Kale is grown as an annual or biennial across USDA zones 2—9. Per Cornell Cooperative Extension, kale is extremely cold-hardy: established plants can withstand temperatures as low as 10°F (—12°C). Per Penn State Extension, \"kale is among the most cold-hardy vegetables available to home gardeners.\"

Seeds germinate at soil temperatures of 45—85°F; optimal germination is at 60—70°F per NC State Extension. Plants grow best at air temperatures of 60—65°F. Heat above 80°F causes bitterness and reduces leaf quality.

In zone 7a (Long Island):

• Spring crop: Direct-sow or transplant 4—6 weeks before last frost (early to mid-March). Harvest through late spring.
• Fall crop (recommended): Direct-sow or transplant in July to early August. Plants establish in late summer heat, then improve dramatically in flavor as temperatures cool in September. Per NC State Extension, frost at 26—28°F improves kale flavor by increasing sugar concentration.
• Overwintering: In zone 7a, fall-planted kale mulched with 2—3 inches of straw often overwinters and resumes spring growth before going to seed in late April.

Seeding and transplanting

Direct seeding: Per Cornell, sow seeds 1/2 inch deep, 1—2 inches apart. Thin to final spacing when plants are 3—4 inches tall.

Transplants: Per Penn State Extension, start seeds indoors 4—5 weeks before transplanting date. Germination is rapid at 65—70°F (5—7 days). Harden off for 7—10 days before transplanting outdoors.

Spacing

Per Cornell Cooperative Extension, thin or space transplants 12—18 inches apart in rows 18—24 inches apart. Per Penn State Extension, for large, bushy plants suitable for continuous leaf harvest, 18-inch spacing is preferred. Tighter spacing (12 inches) produces more upright, less branched plants with similar yield per square foot.

Soil and fertilizing

Per Cornell, kale grows best in fertile, well-drained soil with a pH of 6.0—7.5. It tolerates a wider range of soil conditions than most brassicas.

Fertility: Per NC State Extension, kale responds strongly to nitrogen. Incorporate 2—3 pounds of 10-10-10 per 100 square feet before planting. Side-dress with nitrogen once when plants are half-grown (3—4 weeks after transplanting or thinning): 1/4 cup of 10-10-10 per plant, or Espoma Plant-tone 5-3-3 at 3/4 cup per plant. Per Penn State Extension, excess nitrogen produces very dark green, soft leaves susceptible to aphid colonization.

Boron: Per Cornell, kale, like other brassicas, has a moderate boron requirement. Annual compost incorporation typically provides sufficient boron in most soils; if hollow stems appear, a soil test can confirm deficiency.

Watering

Per Cornell, kale needs 1.5 inches of water per week. Consistent moisture produces tender, mild leaves; drought stress produces bitter, tough leaves. Per NC State Extension, kale's extensive root system makes it more drought-tolerant than shallow-rooted brassicas once established, but quality declines without consistent water.

Soaker hose delivers consistent root-zone moisture without wetting foliage, which reduces fungal disease pressure.

Harvesting

Per Cornell Cooperative Extension, begin harvesting when plants have at least 6—8 leaves. Remove outer, more mature leaves from the base of the plant, leaving the central growing point (the crown) and inner leaves intact. This method allows continuous production from the same plant for months.

Per Penn State Extension, remove no more than 1/3 of the plant's leaves at one harvest. Frequent, partial harvests of this kind can continue until hard freeze in fall or until the plant bolts (sends up a flower stalk) in spring.

Kale leaves are at peak quality in cool weather: tender, mildly sweet, and easy to chew. In summer heat, leaves become tougher, more bitter, and more fibrous. Per NC State Extension, \"a hard frost is almost always good for kale flavor.\"

Overwintering in zone 7a

In zone 7a, fall-planted kale can overwinter with protection. Per Penn State Extension, apply 2—4 inches of straw mulch around the base after hard frost settles. Curly types like 'Winterbor' and 'Dwarf Siberian' handle this best. The plant will slow or stop growth through December—February and resume in March as days lengthen. It will go to seed (bolt) in April—May; harvest the flower shoots, which are edible (similar to broccoli raab), until the plant is spent.

Pests and diseases

Imported cabbageworm and cabbage looper: The same caterpillar complex that affects broccoli and cabbage also targets kale. Per Cornell, imported cabbageworm is the primary caterpillar pest in the Northeast. Agribon row cover from transplanting through harvest excludes the adult butterfly entirely. Per NC State Extension, for spring and fall kale, floating row cover can typically be removed after the first hard frost, as butterfly populations crash at that point.

If caterpillars are present, Monterey BT (Bacillus thuringiensis (BT spray)) applied in late afternoon is the OMRI-listed organic treatment. Apply when larvae are small; older, larger larvae are harder to kill.

Cabbage aphids (Brevicoryne brassicae): Per Penn State Extension, gray-green, waxy aphids that colonize the undersides of leaves and the central growing point. Populations can explode rapidly in spring or fall. Safer insecticidal soap applied directly to aphid colonies; rinse leaves before eating. Per Cornell, encouraging natural enemies (parasitic wasps, ladybird beetles) by avoiding broad-spectrum insecticides supports long-term aphid management.

Downy mildew: Per NC State Extension, yellow patches on upper leaf surfaces with grayish sporulation underneath. More common in fall with cool, wet conditions. Improve airflow; reduce overhead irrigation; choose mildew-tolerant varieties.

Clubroot: Same as broccoli and cabbage — long persistence in soil, reduced by raising pH above 6.5, and managed by not planting brassicas in infected areas.

Common problems

Recommended gear: Best Soaker Hose for Vegetable Gardens (2026) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.

Frequently asked

When does kale taste best?

Per NC State Extension and Cornell, kale's flavor peaks after frost. Cold temperatures cause the plant to convert starches to sugars, producing sweeter, milder leaves. A kale plant that tasted slightly bitter in September will taste noticeably sweeter and more tender after the first hard frost in October. This is not folklore — it is a documented physiological response to cold stress that is consistent across brassica species.

How do I harvest kale for continuous production?

Per Cornell Cooperative Extension, harvest outer leaves from the base of the plant, leaving the central growing crown intact. Never remove more than 1/3 of the plant's total leaf area at one time. This approach allows a single plant to produce leaves for 2—4 months or longer — through the entire fall season in zone 7a and into winter if protected.

Can kale survive winter in zone 7a?

Established kale plants, particularly curly types like 'Winterbor' and 'Dwarf Siberian', can survive zone 7a winters with mulch protection. Per Penn State Extension, established plants tolerate temperatures down to approximately 10°F. In zone 7a, where winter lows typically stay above 0°F, covered plants often survive and resume growth in early spring. Mulch the base with 2—4 inches of straw after the first hard freeze to insulate roots.

What is the difference between kale and collard greens?

Both are Brassica oleracea var. acephala. Per NC State Extension, collard greens have large, smooth, flat leaves and are more heat-tolerant than kale — the preferred leafy green in the South (zones 7—10). Kale has more deeply lobed or curly leaves and is more cold-hardy — the preferred leafy green in the North (zones 3—7). Collards are grown using similar cultural practices to kale but can be direct-seeded in summer in the South for fall and winter harvest.