Arbor

Growing Kale

Updated July 2026

Kale does its best work in cool weather, and the most common timing mistake is treating it as a summer vegetable. For spring, start seeds indoors 4 weeks before your last frost date and transplant outdoors 2 weeks before that date. For a main-season fall harvest, direct sow or set out transplants 6 to 8 weeks before your first expected fall frost. Either way, space plants 18 inches apart and plan on 55 days to full-size leaves — baby leaves are harvestable in about 30 days. The plant tastes noticeably sweeter after a hard frost, so leaving it in the ground longer is almost always better, not worse.

How it works

Kale belongs to the brassica family alongside cabbage, broccoli, and Brussels sprouts. It performs well when temperatures stay below 75°F; above that threshold, UMN Extension notes the plant shifts energy toward reproduction, producing tough, bitter leaves. Below 20°F, leaf tissue begins to take damage, though mature, established plants in favorable conditions can survive harder frosts. The 20-to-75°F window is the productive range, and fall grows squarely in it.

The flavor improvement from frost is real: cool nights prompt the plant to convert starches to sugars. University of Vermont Extension built their fall harvest guidance around this — the longer you leave kale in cool weather, the sweeter it gets. Don’t rush the fall harvest.

Three variants cover most gardens. Curly kale (including Winterbor, which produces harvestable baby greens in about 28 days, and Vates, which is compact and slow to bolt) is the cold-hardiest and most common type. Lacinato (dinosaur kale) has strap-like dark leaves and handles brief heat spikes better than curly types, making it a better choice for warm-climate fall plantings where you’re starting transplants in late summer. Red Russian has tender leaves with purple veins, grows quickly, and is extremely cold-hardy.

Because kale is a brassica, don’t plant it where cabbage, broccoli, or Brussels sprouts grew the previous year. Soil-borne pathogens specific to brassicas persist season to season; annual rotation is the most effective prevention.

What to do

Planting

Kale grows best in full sun — 6 or more hours a day — but tolerates partial shade, especially in warmer zones where afternoon shade extends the productive window.

For spring: start seeds indoors 4 weeks before your last frost date, then move transplants outdoors 2 weeks before that date. Harden off seedlings over 7 to 10 days before setting them out, moving them outdoors for gradually longer stretches so they acclimate. Kale tolerates light freezes and establishes better in cool conditions than in warmth. In spring, skip direct sowing and use transplants; the season is too short to waste time on germination in the ground.

For fall (the main season in most climates): direct sow or set out transplants 6 to 8 weeks before your first expected fall frost. If you direct sow, thin seedlings to 18 inches apart once they reach 3 to 4 inches tall, keeping the strongest plant at each spot. NC State Extension uses six weeks before first frost as the benchmark. For a steady supply rather than a single flush, University of Vermont Extension recommends starting new transplants every 3 to 4 weeks through the season.

Soil and fertilizing

Before planting, incorporate 3 to 4 inches of compost into the planting area — kale is a moderate to heavy nitrogen feeder and benefits from that base. If you’re using a granular fertilizer at planting, a balanced blend supports strong establishment. Four weeks after transplanting or thinning, side-dress with nitrogen: USU Extension recommends 1/2 cup of 21-0-0 fertilizer per 10 feet of row. Repeat monthly through the growing season.

When you add kale to your garden in Arbor, it schedules a side-dressing reminder 4 weeks after your transplant date — the maintenance step that’s easiest to lose track of when you’re managing multiple beds at once.

Watering

Water established plants every 4 days under normal conditions. When temperatures push above 85°F, increase frequency. Consistent moisture produces tender leaves; drought stress produces tough, bitter ones.

Harvest

Harvest outer leaves when they reach 8 to 10 inches long, leaving several young inner leaves and the central growing point untouched. NC State Extension recommends removing no more than one-third of the plant per harvest. With this outer-leaf approach, University of Vermont Extension describes a continuous harvest that runs through multiple frosts — a single planting can produce for months.

Remove yellowed or damaged leaves whenever you spot them; they won’t recover and draw resources away from productive growth.

Pests

Cabbage worms, aphids, and cabbage borers are the primary threats. Row covers installed over young transplants provide effective protection before pest populations build. Remove the covers 3 to 4 weeks after transplanting, once plants are actively growing and large enough to tolerate moderate pest pressure. If cabbage worms are already present, hand-pick them and the pale-yellow egg clusters on leaf undersides and drop them in soapy water. For aphids, a firm spray of water knocks most of the colony off; repeat every few days until numbers drop.

Zone and season notes

Zones 3–5: Spring is a short but real window; fall is the main event. Direct sow by late July to early August in most of this range. Mature plants can overwinter under heavy mulch, giving an early-spring harvest from the previous season’s planting before new transplants are ready.

Zones 6–7: Both spring and fall plantings are productive. Fall-planted kale often carries through winter with minimal protection and produces new growth in early spring, ahead of fresh transplants.

Zones 8–9: Fall through spring is the primary window. Clemson HGIC and NC State Extension both frame kale guidance around fall timing in these zones; summer heat makes productive kale nearly impossible. Lacinato handles brief late-summer warmth better than curly types, which matters for fall transplants started in August.

Zones 10–11: Same fall-through-spring window. Afternoon shade can push the spring harvest a few weeks further, but once daytime temperatures consistently exceed 85°F, quality drops fast. Succession plantings every 3 to 4 weeks matter most here, where the productive window is bounded on both sides.

Sources

  • UMD Extension — Growing Leafy Greens in a Home Garden — extension.umd.edu/resource/growing-leafy-greens-home-garden
  • Clemson HGIC — Kale Is a Headless Cabbage — hgic.clemson.edu/kale-is-a-headless-cabbage/
  • USU Extension — How to Grow Kale in Your Garden — digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1274&context=extension_curall
  • UMN Extension — Growing Collards and Kale in Home Gardens — extension.umn.edu/vegetables/growing-collards-and-kale
  • NC State Extension — Kale — content.ces.ncsu.edu/kale
  • University of Vermont Extension — Kale for Autumn Harvest — uvm.edu/extension/news/kale-autumn-harvest
  • West Virginia University Extension — Growing Kale — extension.wvu.edu/lawn-gardening-pests/gardening/wv-garden-guide/growing-kale-in-west-virginia