How to Grow Kale in Cold Climates: When to Plant, Best Varieties & Care

Intro for growing kale in cold climates

Kale is a nutritional powerhouse and cold-weather champion in the vegetable garden. This leafy green member of the Brassica family thrives when temperatures drop, actually improving in flavor after frost exposure. For gardeners in cold climates, kale offers the perfect opportunity to extend the growing season well into winter, providing fresh greens when other vegetables have long since succumbed to freezing temperatures. With its impressive cold hardiness (surviving temperatures as low as -15°C/5°F in some varieties), high vitamin content, and versatility in the kitchen, kale deserves a prime spot in any cold-climate garden. Whether grown in raised beds, traditional plots, or containers, kale rewards gardeners with abundant harvests through the coldest months of the year.

When to plant kale in cold climates

In cold climates, kale can be planted during two primary windows. For a fall/winter harvest, sow seeds in mid to late summer (July to August), allowing plants to mature as temperatures cool. For spring harvests, plant as soon as soil can be worked, typically 4-6 weeks before the last frost date. Kale seeds germinate best in soil temperatures between 7-30°C (45-85°F), with optimal germination at 21°C (70°F). Unlike many vegetables, kale actually improves after light frosts, which convert starches to sugars and enhance flavor. In zones 7 and colder, kale can overwinter with proper protection, providing an early spring harvest before bolting as days lengthen.

Best time to plant kale in cold climates

For cold climate regions (USDA zones 3-6, UK hardiness zones 7-9), the ideal planting windows are:

Spring planting: Direct sow seeds 4-6 weeks before last frost (typically March to April) or start indoors 6-8 weeks before last frost for transplanting in April to early May.

Fall planting: Direct sow 10-12 weeks before first expected frost (typically late July to mid-August) or start indoors for transplanting 8-10 weeks before first frost. This timing allows plants to establish before severe cold while benefiting from flavor-enhancing light frosts.

In extremely cold regions (zones 3-4), starting indoors and using season extension methods like cold frames or row covers will significantly improve success rates for both planting windows.

Best kale varieties to grow in cold climates

• Winterbor – Exceptionally cold-hardy with tightly curled blue-green leaves that stand up to freezing temperatures down to -15°C (5°F).
• Red Russian – Beautiful purple-veined, oak-leaf shaped foliage that’s tender even when mature and survives temperatures to -12°C (10°F).
• Lacinato (Dinosaur/Tuscan) – Dark blue-green, heavily textured leaves with excellent flavor that improves dramatically after frost.
• Redbor – Stunning magenta-purple curly leaves that intensify in color with cold weather, making it both ornamental and edible.
• Dwarf Blue Curled Scotch – Compact plants ideal for containers with tightly curled blue-green leaves and exceptional cold hardiness.
• Siberian – Flat, tender leaves with wavy edges that offer supreme cold tolerance, often surviving under snow cover.
• Western Front – Modern hybrid with excellent disease resistance and remarkable winter hardiness in northern climates.

How to plant kale in cold climates

Materials needed:

• Kale seeds or seedlings
• Compost or aged manure
• Balanced organic fertilizer
• Garden fork or tiller
• Row cover or cold frame (for extreme climates)
• Mulch material (straw, leaves, or compost)
• pH testing kit (optional)

Step-by-step planting:

1. Select a site with at least 6 hours of sun daily (partial shade is acceptable in hotter regions).
2. Test soil pH and aim for 6.0-7.0; add lime if soil is too acidic.
3. Prepare soil by incorporating 2-3 inches (5-7.5 cm) of compost or aged manure.
4. For direct sowing, plant seeds 1/4 to 1/2 inch (0.6-1.2 cm) deep in rows 18-24 inches (45-60 cm) apart.
5. Space seeds 3 inches (7.5 cm) apart, planning to thin to 12-18 inches (30-45 cm) once seedlings establish.
6. For transplants, dig holes slightly larger than the root ball and space plants 12-18 inches (30-45 cm) apart.
7. Water thoroughly after planting to settle soil around seeds or roots.
8. Apply a 2-inch (5 cm) layer of mulch around plants (but not touching stems) to regulate soil temperature and moisture.
9. In extremely cold regions, install row covers or cold frames to provide additional protection.

How to grow kale in cold climates

Kale thrives in full sun to partial shade, with northern gardens benefiting from maximum sunlight exposure. Water consistently, providing 1-1.5 inches (2.5-3.8 cm) weekly, focusing on deep watering rather than frequent shallow irrigation. Maintain even soil moisture, especially during dry periods, as drought stress contributes to bitter flavor.

Feed plants monthly with balanced organic fertilizer or compost tea, reducing to every 6-8 weeks during winter. Apply a nitrogen-rich side dressing mid-season for leafy growth. Mulch heavily (3-4 inches/7.5-10 cm) around plants in late fall to insulate roots from extreme temperature fluctuations.

For container growing, select pots at least 12 inches (30 cm) deep with adequate drainage. Use premium potting mix amended with compost, and choose compact varieties like ‘Dwarf Blue Curled Scotch.’ Container-grown kale requires more frequent watering and feeding but can be easily moved to protected locations during extreme cold.

In zones 3-5, provide additional protection with deep mulch, row covers, or cold frames when temperatures consistently drop below -12°C (10°F). Remove yellowing lower leaves promptly to improve air circulation and prevent disease.

Caring for kale in cold climates

Regular monitoring is essential for successful kale cultivation in cold climates. Check plants weekly for pests like aphids, cabbage worms, and flea beetles. For aphids, spray plants with strong water jets or insecticidal soap; for cabbage worms, apply Bacillus thuringiensis (Bt); and for flea beetles, use row covers during establishment.

Watch for signs of common diseases including powdery mildew (white powdery coating on leaves) and black rot (yellow V-shaped lesions). Prevent these by maintaining good air circulation, practicing crop rotation, and avoiding overhead watering. Remove and destroy affected leaves immediately.

Harvest kale when leaves reach desired size, typically 8-10 inches (20-25 cm) long, starting with the lowest, oldest leaves first. After frost, wait until midday when plants have thawed before harvesting to prevent cell damage. For winter harvests in very cold regions, prioritize picking before deep freezes or heavy snow.

Store harvested kale in the refrigerator for 1-2 weeks in perforated plastic bags, or blanch and freeze for longer preservation. For continuous production, harvest regularly, taking no more than one-third of the plant at once.

Understanding bolting in kale

Bolting is the process where kale shifts from leaf production to flowering and seed production, rendering leaves bitter and tough. In cold climates, kale typically bolts in spring as days lengthen and temperatures rise. The primary triggers include increasing day length (photoperiod), sustained temperatures above 24°C (75°F), and environmental stressors like drought or root disturbance.

To prevent premature bolting, select slow-bolting varieties like ‘Winterbor’ or ‘Western Front’ for cold climates. Plant fall crops early enough to establish before winter but late enough to avoid early fall heat. Provide consistent moisture and apply mulch to moderate soil temperature fluctuations. For spring plantings, start as early as possible to maximize growth before summer heat triggers bolting.

If kale begins to bolt, harvest all usable leaves immediately. The central flowering stalk can be cut and eaten when young and tender. Consider allowing a few plants to complete their lifecycle and collect seeds for future plantings, as these may develop increased cold adaptation for your specific microclimate.

Why does kale turn bitter?

• Heat stress – Temperatures consistently above 24°C (75°F) trigger defensive compounds; solution: provide afternoon shade or use row covers during heat waves.
• Age – Older leaves naturally accumulate more bitter compounds; solution: harvest regularly, focusing on younger leaves during warm periods.
• Water stress – Inconsistent watering increases bitterness; solution: maintain even soil moisture with regular deep watering and mulching.
• Bolting initiation – Even before visible flowering, internal hormonal changes increase bitterness; solution: harvest entire plant once bolting begins.
• Soil mineral imbalance – Insufficient potassium or excessive nitrogen can affect flavor; solution: conduct soil test and amend accordingly with balanced organic fertilizers.

Companion planting for kale

Good companions:

• Alliums (onions, garlic, chives) – Repel cabbage worms and other kale pests with their strong scent.
• Aromatic herbs (mint, sage, dill, chamomile) – Confuse and deter pest insects while attracting beneficial predators.
• Beets – Different root depth means they don’t compete for nutrients, and they thrive in similar conditions.
• Nasturtiums – Act as trap crops for aphids and other pests that would otherwise attack kale.
• Spinach – Quick-growing crop that can be harvested before kale reaches full size, maximizing garden space.

Avoid planting near:

• Strawberries – Compete for similar nutrients and can inhibit kale growth.
• Other brassicas (cabbage, broccoli, cauliflower) – Share same pests and diseases, potentially magnifying problems.
• Sunflowers – Cast too much shade and secrete compounds that can inhibit kale growth.

Seasonal calendar

• January-February: Plan garden; order seeds; harvest overwintered kale on mild days.
• March: Start seeds indoors for spring planting; prepare garden beds.
• April: Direct sow as soon as soil can be worked; transplant seedlings with protection; harvest overwintered kale.
• May: Continue harvesting spring kale; apply first fertilizer; monitor for pests.
• June: Harvest spring kale before summer heat; apply mulch to retain moisture.
• July: Harvest remaining spring kale; prepare beds for fall planting; start seeds indoors for fall crop.
• August: Direct sow fall/winter crop; transplant seedlings; provide shade if temperatures are high.
• September: Continue planting for fall harvest; fertilize established plants; begin harvesting early varieties.
• October: Harvest regularly; prepare for frost protection; enjoy sweeter flavor after first light frosts.
• November: Apply heavy mulch for winter protection; continue harvesting; install row covers or cold frames.
• December: Harvest during mild spells; maintain winter protection; enjoy cold-sweetened kale.

Problems & solutions

Common questions about growing kale in cold climates

Q: How much sunlight does kale need in cold climates?
A: In cold climates, kale benefits from full sun (6+ hours daily). During summer heat, light afternoon shade can prevent stress and bitterness, but maximum sunlight is advantageous during fall and winter months.

Q: Can I grow kale in containers through winter?
A: Yes, but use containers at least 12 inches (30 cm) deep and 12 inches (30 cm) in diameter per plant. Container-grown kale requires additional winter protection as roots are more vulnerable to freezing. Move pots to sheltered locations or insulate with bubble wrap, straw, or burlap when temperatures drop below -7°C (20°F).

Q: How often should I harvest kale in winter?
A: During winter, kale grows very slowly or may become dormant in extremely cold regions. Harvest during warmer spells when plants are not frozen, taking only what you need and leaving at least the central growing point and several healthy leaves to ensure continued production when growth resumes.

Q: What’s the minimum temperature kale can survive?
A: Most kale varieties can survive temperatures down to -12°C (10°F) without protection. Hardy varieties like ‘Winterbor’ and ‘Siberian’ can withstand temperatures as low as -18°C (0°F) with proper mulching. Below these temperatures, row covers, cold frames, or deep snow cover provide necessary insulation.

Q: How do I prevent kale from being buried by snow?
A: Before heavy snowfall, create a simple hoop structure with PVC pipes or flexible rods covered with row cover fabric or clear plastic. This creates a protective dome that prevents snow from crushing plants while still allowing light penetration. Alternatively, place evergreen boughs around plants to support snow weight.

Q: Why did my overwintered kale start flowering in early spring?
A: Overwintered kale naturally flowers (bolts) in spring as day length increases. This is part of its biennial lifecycle. For continuous leaf production, sow new kale in early spring to replace overwintered plants. Alternatively, harvest the flowering shoots (raab) which are tender and delicious before flowers fully open.

Q: Can I save seeds from my cold-hardy kale?
A: Yes, and it’s beneficial! Allow overwintered plants to flower and set seed pods. When pods turn brown but before they split, harvest entire stalks and dry in paper bags. Plants that survive your specific winter conditions will produce offspring with enhanced cold hardiness for your microclimate.