Kale

Kale (Brassica oleracea var. acephala) is the workhorse brassica of the cool-season garden. It tolerates light frost better than almost any other leafy crop - in fact, cold temperatures below 28°F convert leaf starches to sugars and improve the flavor noticeably. You can harvest kale from spring through the first hard freeze in most zones, and in Zones 7 and warmer, through winter with light protection. For production across the widest temperature range, it’s hard to beat.

What you’re choosing between

Kale cultivars are grouped primarily by leaf texture and cold tolerance, and the differences matter for how you use the harvest.

Curly kale (Vates, Winterbor) is the type in most grocery stores - heavily crinkled, fairly tough leaves. It’s the hardiest type and holds its quality the longest in the garden. Best for cooking; the texture can be aggressive when raw.

Lacinato (Tuscan/Dinosaur) kale (B. oleracea ‘Lacinato’) has dark blue-green, puckered strap-shaped leaves. Less cold-hardy than curly types but better flavor for raw applications and lighter cooking. The standard in Italian cooking (cavolo nero). More widely available at specialty retailers where it runs $4–$6/lb.

Siberian kale (Brassica napus, which is technically a different species) is the most cold-tolerant type - it can survive temperatures into the single digits Fahrenheit without cover in established stands (University of Vermont Extension, Brassica Crops, 2020). Leaves are blue-green, smoother than curly kale, and mildly flavored. Excellent for zone 3–4 gardeners who need a brassica that actually survives.

Ruvo kale (Brassica ruvo, also called Italian sprouting broccoli or cima di rapa) is grown primarily for its young shoots and flower buds rather than mature leaves. It’s a different product from typical kale - more like broccolini in use, harvested before the flowers open.

For most home gardens: if you want the biggest yield and longest season, grow Vates or Winterbor curly kale. If you’re cooking Italian, go Lacinato. If you’re in zone 3–4, Siberian.

The ROI case

A $3.00 seed packet plants far more starts than most home gardens need. Kale is direct-seeded or transplanted; seed to transplant is 4–6 weeks, and direct seeding outdoors can begin 4 weeks before last frost. A well-managed cut-and-come-again plant yields roughly 2 lb of leaves across the full season (USDA NASS specialty crop surveys; variety trial data from Cornell Small Farms Program). At $3.50/lb (USDA AMS retail price data for fresh kale, 2023), that’s $7 per plant in grocery value from $0.10–$0.15 in seed cost.

The economics aren’t as dramatic as basil or specialty tomatoes, but kale plants six to eight weeks before last frost date extend into seasons where most other crops have quit. The real value argument is in the shoulder seasons - kale in November and March when your other beds are empty.

Growing requirements

Kale is a cool-season biennial grown as an annual. Soil temperature of 45–85°F for germination - it’s a wide range, which is why kale can be direct-seeded much earlier in spring than warm-season crops. Optimal germination is at 60–65°F (Cornell Cooperative Extension, Kale Production, 2018).

For spring production: sow outdoors 4–6 weeks before last frost, as soon as the soil can be worked and temps are consistently above 40°F. For fall production: sow 8–10 weeks before first fall frost; the plants will size up in late summer and improve through autumn frosts.

Space transplants 18–24 inches apart. Kale grows large - a single Vates plant at full maturity can span 2 feet across and produce leaves continuously for months. Crowded plants have worse airflow and more disease pressure.

Soil pH of 6.0–7.0. Kale is a moderate feeder; a soil amendment with compost before planting plus a nitrogen-forward fertilizer (blood meal, 8-1-1 granular, or similar) every 4–6 weeks supports leaf production. Nitrogen-deficient kale turns pale yellow-green and produces small leaves with poor flavor.

The cut-and-come-again technique: harvest outer leaves first, always leaving the central growing point and at least four to six inner leaves intact. The plant continues producing from the center. Stripping a plant to the stem kills it. Harvest every 7–14 days through the season to keep production going.

What goes wrong

Imported cabbageworm (Pieris rapae) and cabbage loopers (Trichoplusia ni) are the primary caterpillar pests. Both leave large irregular holes in leaves. The eggs of the imported cabbageworm are tiny yellow footballs, single, on leaf undersides; loopers are light green caterpillars that move with a looping motion. Bacillus thuringiensis var. kurstaki (Bt) spray is highly effective when applied while caterpillars are small. Row cover over young transplants prevents adult butterflies and moths from laying eggs; remove it if temperatures inside the cover become excessive.

Aphids - particularly the cabbage aphid (Brevicoryne brassicae) - can form dense gray-green colonies in the leaf axils. They’re especially damaging on growing tips. A hard water blast removes most colonies; insecticidal soap handles heavier infestations. Parasitic wasps are effective natural controls; avoid broad-spectrum insecticides that kill parasitoids along with aphids.

Clubroot (Plasmodiophora brassicae) causes distorted, swollen roots and yellowing, wilted plants. It’s a soilborne slime mold that persists for decades in acidic soil. Raising soil pH above 7.2 by liming reduces clubroot pressure significantly (Penn State Extension, Crucifer Diseases, 2019). Rotate brassicas out of infected beds every 3–4 years.

Black rot (Xanthomonas campestris pv. campestris) enters through leaf margins, causing V-shaped yellow lesions that progress inward. It’s seedborne and spreads in wet conditions. Use certified disease-free seed; avoid overhead irrigation; remove and bag infected plants.

Harvest and storage

Harvest leaves in the morning. Use a sharp knife or scissors to remove outer leaves cleanly - tearing risks snapping the leaf near the midrib and leaving stubs that rot. Kale holds in the refrigerator for 1–2 weeks - longer than most leafy greens because its tougher cell walls slow moisture loss.

For cooking, the center midrib on larger leaves is fibrous and often removed by stripping the leaf away from both sides. Small and medium leaves can be cooked whole. Kale softens significantly with heat; the bite that seems aggressive raw largely disappears after 5 minutes of cooking.

For storage: blanch and freeze for 8–10 months of acceptable quality (National Center for Home Food Preservation, Freezing Vegetables, 2021). Kale chips are a practical way to use surplus - the dehydration concentrates flavor and the chips store at room temperature for weeks.

---

Related crops: Lettuce, Garlic

Related reading: Spring Garden Planning - how to time your cool-season plantings around frost dates to maximize the shoulder seasons