Growing Kale: A US Guide

Why kale is worth growing in US gardens

Kale is one of the most productive cool-season vegetables for US home gardeners. A single plant, harvested from the outside in, produces usable leaves for 8–12 weeks or longer in the right conditions.

The economics are compelling: a six-pack of kale transplants costs $4–6 at most garden centers and produces more than most households can use in a season. For gardeners in Zones 5–8 who plant in late summer (July 20–August 15 depending on location), fall kale is ready from September through November or later.

Understanding kale’s basic biology makes growing it simple. It’s a Brassica oleracea — the same species as broccoli, cabbage, and Brussels sprouts — and shares those crops’ preference for cool weather, rich soil, and consistent moisture. What distinguishes kale is that it tolerates cold better than most related crops: established plants survive temperatures as low as 10°F in many varieties.

For an overview of planning a full cool-season garden that integrates kale with other leafy greens, our how to start a vegetable garden guide covers crop sequencing and bed preparation.

Kale varieties: which to grow

The variety choice affects texture, flavor, cold tolerance, and harvest timing.

For most US gardeners: ‘Red Russian’ and ‘Lacinato’ are the easiest to start with. Both are widely available, productive, and flavorful. ‘Red Russian’ is the best choice if you want to eat kale raw; its leaves are more tender than curly varieties.

For cold-climate gardeners (Zones 3–5): ‘Winterbor’ and ‘Premier’ overwinter or produce into late November. ‘Winterbor’ is the most cold-tolerant variety tested in university extension trials.

For southern US gardeners (Zones 8–9): Focus entirely on fall and winter planting. ‘Red Russian’ bolts fastest in heat; choose ‘Redbor’ or a heat-tolerant curly type if spring weather arrives suddenly.

Planting timing by USDA zone

Kale fails when soil temperatures exceed 75°F at germination or when heat arrives before plants are established. Timing prevents this.

Spring planting

Start seeds indoors 6 weeks before your last average frost date. Transplant outdoors 2–4 weeks before last frost when soil is workable. Kale tolerates light frosts at the transplant stage.

Zone 9 note: Spring kale almost always fails in Zone 9 because heat arrives before plants mature. Focus entirely on fall and winter planting.

Fall planting (recommended for most zones)

Fall-planted kale tastes better, grows longer, and has fewer pest problems than spring-planted kale in most of the US.

Count back from your average first fall frost date. Plant direct seeds 8 weeks before frost; transplants 6 weeks before frost.

Soil preparation

What kale needs from soil

Kale is a heavy feeder. It performs best in:

• pH 6.0–7.0 — slightly acidic to neutral. Test with an inexpensive kit or contact your local cooperative extension. Most US soils in this range.
• High nitrogen — kale produces large amounts of leafy biomass. Soil low in nitrogen produces pale, slow-growing plants with small leaves.
• Good drainage — standing water for more than 24 hours causes root rot in Brassicas.

Soil amendment rates

Before planting, work these amendments into the top 8–10 inches of soil:

• Compost: 3–4 inches mixed in thoroughly. Compost provides slow-release nutrients and improves drainage in clay soils.
• Balanced granular fertilizer (10-10-10): Apply at 2 lbs per 100 square feet if your soil tests low in phosphorus and potassium.
• Blood meal or feather meal (if nitrogen is low): Apply at manufacturer’s rate. These are high-nitrogen organic amendments that break down over 4–6 weeks.

Testing soil pH is worthwhile if you’ve had poor results with Brassicas before. Our how to test soil pH guide explains the process and how to interpret results.

Planting method

Starting from seed (direct sowing)

Direct sowing is simpler for fall planting. Kale germinates in 5–10 days when soil is between 45–85°F.

1. Prepare a fine seedbed — rake out clods so seeds make good soil contact.
2. Sow seeds ¼ inch deep, spaced 1 inch apart in rows 18 inches apart.
3. Thin to 18–24 inches when seedlings are 4 inches tall. Thinnings are edible.
4. Water gently so seeds don’t wash out.

Starting from transplants (indoor seed starting)

Transplants give you a head start in spring and reduce the uncertainty of summer heat for fall planting.

1. Fill cell trays or 4-inch pots with seed-starting mix.
2. Plant 2 seeds per cell, ¼ inch deep.
3. Germination happens in 5–8 days at 65–75°F.
4. Thin to one seedling per cell after germination.
5. Keep under grow lights for 14–16 hours daily or in a south-facing window.
6. Harden off over 7–10 days before transplanting: start with 1–2 hours of outdoor exposure and increase daily.

Spacing

18–24 inches between plants is the standard recommendation. Tighter spacing (12 inches) works if you plan to harvest young leaves constantly. The main consequence of crowding is reduced airflow, which increases the risk of fungal diseases like downy mildew.

Fertilizing

Kale needs nitrogen throughout the growing season. Without consistent nitrogen, older leaves turn yellow from the bottom of the plant upward.

At planting: Work compost and a balanced fertilizer into soil as described above.

4–6 weeks after transplanting: Side-dress plants with ½ cup of balanced granular fertilizer per 10 feet of row, or water in a liquid fertilizer (fish emulsion works well) at the manufacturer’s rate.

Signs of nitrogen deficiency: Pale yellow leaves starting at the base, slow growth, small new leaves.

Avoid over-fertilizing with nitrogen in fall — late-season nitrogen flushes produce soft growth that winter cold damages more severely.

Watering

Kale needs 1–1.5 inches of water per week. Drought stress causes bitterness and makes plants more susceptible to aphid infestations.

• Drip irrigation is ideal. It delivers water to the root zone without wetting leaves, reducing disease.
• Overhead watering works but do it in the morning so leaves dry before evening.
• Mulch helps retain moisture. A 2-inch layer of straw or wood chip mulch reduces watering frequency by 30–40% in most conditions.

Kale wilts visibly when drought-stressed but usually recovers fully after watering. Repeated wilting stunts growth.

Pest and disease management

Kale’s main pests in the US are:

Cabbage loopers and imported cabbageworm

The pest: Pale green caterpillars that chew irregular holes through leaves. Adults are white or brown moths. Most problematic in spring and early fall.

The fix: Row cover from planting is the most effective prevention — it stops moths from laying eggs. For established infestations, Bacillus thuringiensis (Bt) spray kills caterpillars without harming beneficial insects. Apply at the first sign of damage.

Aphids

Small, soft-bodied insects that cluster on leaf undersides and growing tips. They cause leaf curling and stunted growth. Fall-planted kale has fewer aphid problems than spring-planted kale.

The fix: Knock off with a strong water spray. Neem oil spray works for moderate infestations. Beneficial insects — ladybugs, parasitic wasps — provide natural control if you avoid broad-spectrum pesticides.

Harlequin bugs

Distinctive red-and-black stink bugs that suck plant sap, causing white or yellow spots. Common from Zone 7 southward from April through October.

The fix: Hand-pick adults and egg masses daily in early infestations. Neem oil spray may deter feeding. Row cover from planting prevents access.

Downy mildew

Yellow patches on leaf tops with gray-purple fuzzy growth on undersides. Common in cool, humid conditions.

The fix: Improve air circulation by removing crowded plants. Avoid overhead watering. Plant resistant varieties like ‘Winterbor’. The disease is cosmetic — infected leaves are edible if you cut out affected areas.

For general cabbage-family pest management, our companion plants for cabbage guide covers companion planting strategies that reduce pest pressure.

Harvesting kale

The most important harvest technique for continuous production: take the outer leaves first, leave the growing tip.

How to harvest correctly

1. Identify the central growing point at the top of the plant — leave this intact.
2. Snap or cut the outer leaves at the base of the stem, working from the lowest leaves upward.
3. Remove no more than 30–40% of the plant’s leaves at any single harvest.
4. Return every 1–2 weeks for the next harvest as new leaves grow from the center outward.

When leaves are ready

Harvest baby kale leaves when they’re 4–6 inches long for salads. For cooking, wait until leaves are 8–12 inches long and deep green (or purple in colored varieties). Overly large, old leaves become tough and fibrous.

After frost: Wait 24–48 hours after a frost for maximum sweetness. Cold converts starches to sugars — the flavor difference between pre-frost and post-frost kale is noticeable. In Zones 5–6, November kale from well-established plants is often the sweetest of the season.

Extending the season

Row cover

Floating row cover adds 4–8°F of frost protection. A single layer keeps kale productive through temperatures as low as 20°F in most varieties. Use wire hoops to keep cover from lying on leaves — direct contact on cold nights can still damage leaves.

Cold frames

A simple cold frame (low box with a glass or clear plastic lid) extends kale harvest into December or January in Zones 5–7. Ventilate on sunny days above 40°F to prevent overheating.

Hoop house

In Zones 6–7, an unheated hoop house protects kale through most winters, allowing harvests from November through March. University extension trials at Penn State found kale in unheated tunnels was harvestable in 14 of 15 winters tested.

Kale next to other crops

Kale does well planted near:

• Beets: Neither competes aggressively; beets fix no nitrogen so they don’t interfere with kale’s needs.
• Onions and garlic: Repel some Brassica pests including aphids and cabbage loopers.
• Nasturtiums: Trap crops that attract aphids away from kale.
• Herbs (dill, chamomile): Attract beneficial insects that prey on caterpillars.

Avoid planting kale near other Brassicas like broccoli, cabbage, or Brussels sprouts if you can — they share the same pests and diseases, concentrating problems in one area.

Our companion planting chart has a complete list of what grows well together in the vegetable garden.

Storing kale

Fresh kale keeps in the refrigerator for 1–2 weeks unwashed, stored in a plastic bag or airtight container. Wash immediately before use.

Freezing: Blanch leaves in boiling water for 2 minutes, then plunge into ice water for 2 minutes. Drain, pat dry, and freeze in a single layer before transferring to freezer bags. Blanched kale keeps for 10–12 months.

Dehydrating: Kale chips are made by drying leaves at 135°F for 3–4 hours in a food dehydrator, or in an oven at 170°F for 20–30 minutes. Season before drying.

For more on preserving the vegetable garden harvest, our guide on how to dry herbs covers similar dehydration techniques that apply to leafy greens.

Sources: USDA ERS Kale Data; Penn State Extension Cool Season Vegetables; University of Minnesota Extension Kale Growing Guide.