When is the best time to plant kale in the USA? - Plant Care Guide

The best time to plant kale in the USA is typically early spring for a spring/early summer harvest, and late summer to early fall for a fall/winter/early spring harvest. As a versatile and remarkably cold-hardy cool-season vegetable, kale can often provide two main harvesting windows, with optimal planting times determined by your specific USDA Hardiness Zone and local climate to avoid extreme summer heat and ensure maturity before deep winter cold.

What defines kale as a cool-season crop?

Kale (Brassica oleracea var. sabellica) is definitively defined as a cool-season crop because its optimal growth and flavor development occur in moderate to cool temperatures, rather than the intense heat of summer. This preference dictates its ideal planting times and makes it a staple for spring and fall gardens.

Here's what defines kale as a cool-season crop:

1. Optimal Temperature Range:

   • Kale thrives in temperatures between 60-70°F (15-21°C). This is its sweet spot for vigorous growth and tender leaf development.
   • Seed Germination: Seeds germinate best in soil temperatures ranging from 40-75°F (4-24°C), making it suitable for early spring sowing.

2. Cold Hardiness:

   • This is its most defining cool-season trait. Kale is remarkably cold-hardy, tolerating light frosts (down to mid-20s°F / -4°C) without significant damage.
   • Many varieties can even survive hard freezes (into the low teens or single digits Fahrenheit, -10°C to -18°C) with proper protection, allowing for extended fall and winter harvests.
   • Flavor Enhancement: Exposure to frost actually sweetens kale's flavor, as the plant converts starches to sugars to act as natural antifreeze, improving palatability.

3. Heat Sensitivity:

   • Bolting: When temperatures consistently rise above 75-80°F (24-27°C), kale becomes stressed. It tends to "bolt" – send up a tall central flower stalk and go to seed. Bolting signals the end of its leafy production.
   • Bitterness/Toughness: Hot temperatures also cause kale leaves to become tough, fibrous, and develop a bitter flavor, making them less palatable.

4. Growth Cycle:

   • Its typical growth cycle is optimized for spring and fall. Planted in spring, it matures before summer heat. Planted in late summer/fall, it matures in the cooling temperatures of autumn and then holds through winter.

Because of these characteristics, gardeners strategically time their kale plantings to fall within the cool periods of spring and autumn, avoiding the summer heat, to ensure the best possible flavor and longest harvest.

When is the best time to plant kale in spring?

The best time to plant kale in spring is as soon as the soil can be worked and when temperatures are reliably cool, typically 4-6 weeks before your last average frost date. This early planting window allows kale to establish and mature before the onset of summer heat, which can cause bitterness and bolting.

Here's how to time your spring kale planting:

1. Direct Sowing Outdoors:

   • Timing: Plant kale seeds directly into the garden bed or containers as soon as the soil thaws and can be worked in early spring. This is usually when daytime temperatures are consistently in the 50s-60s°F (10-15°C).
   • USDA Zone Guidance:
     • Southern US (Zones 8-10): February to March.
     • Mid-Atlantic/Southeast (Zones 6-7): March to early April.
     • Northeast/Midwest (Zones 4-5): April to early May.
   • Benefits: Kale seeds germinate well in cool soil, and direct sowing avoids transplant shock.
   • Look for: Kale seeds for spring planting.

2. Planting Transplants (Starts):

   • Timing: If you purchase kale plant starts from a nursery or start them indoors yourself, plant them outdoors in early spring around your last average frost date, or a little earlier (1-2 weeks before) if they are hardened off and a light frost is not expected to be severe.
   • Why Transplants: Allows for an earlier harvest, especially in regions with short springs before summer heat.
   • Hardening Off: If starting seeds indoors, ensure seedlings are gradually acclimated to outdoor conditions for 7-10 days before transplanting to reduce shock.

Key Considerations for Spring Planting:

• Soil Temperature: Aim for soil temperatures above 40°F (4°C) for best germination.
• Succession Planting (Optional): For a continuous spring harvest, you can plant small batches of kale seeds or starts every 2-3 weeks for a few cycles, especially for leafy greens that you harvest frequently. However, stop planting when consistent hot summer temperatures are predicted to avoid bolting.
• Heat-Tolerant Varieties: If you push your spring planting later into warmer weather, or live in a hotter Zone 7/8, choose "slow-bolting" or "heat-tolerant" kale varieties to extend the harvest.

By planting kale early in spring, you leverage its cold-hardiness and preference for moderate temperatures, ensuring a tender and delicious harvest before the summer heat encourages bitterness and bolting.

When is the best time to plant kale for a fall and winter harvest?

The best time to plant kale for a fall and winter harvest is late summer to early fall, several weeks before your first expected hard frost. This allows the kale plants to become well-established and grow to a good size before the onset of truly cold weather, which is crucial for their survival and continued production through winter.

The exact timing will vary significantly by your USDA Hardiness Zone and local climate:

1. For Zones 7-8 (Milder Winters, Good Overwintering):

   • Timing: Plant seeds or transplants in late August to early September.
   • Reason: This gives the plants ample time (6-8 weeks) to grow robust roots and a decent amount of foliage before consistent freezing temperatures arrive. They'll likely provide a good harvest in late fall and then continue producing through winter, especially with minimal protection.
   • Harvest Window: Late fall, winter, and a strong flush in early spring.

2. For Zones 5-6 (Colder Winters, Possible with Protection):

   • Timing: Plant seeds or transplants in mid-July to mid-August. You need an earlier start compared to warmer zones.
   • Reason: The goal is to get large, established plants that have built up their cold-hardiness and energy reserves before deep cold sets in.
   • Harvest Window: Late fall, potentially intermittent winter harvests on milder days, and a robust early spring flush. Protection (row covers, cold frames) is highly recommended.

3. For Zone 4 (Very Cold Winters, More Challenging):

   • Timing: Plant seeds or transplants in late June to mid-July. This requires careful planning to avoid intense summer heat stress during establishment.
   • Reason: The longest establishment period is needed before hard freezes begin.
   • Harvest Window: Primarily a late fall harvest, with very limited winter harvests even with heavy protection. Main benefit is a very early spring harvest.

Key Principles for Fall/Winter Planting:

• Count Back from First Frost: A common rule is to count back 6-8 weeks from your first average fall frost date to determine the latest ideal planting window. This allows plants to reach maturity before cold dormancy.
• Transplants Can Help: If your summer heat extends late, or your fall growing season is short, starting seeds indoors 4-6 weeks before your target outdoor planting date and then transplanting hardened-off starts can be beneficial. You can find kale plant starts at nurseries.
• Cold-Hardy Varieties: Always choose cultivars specifically bred for cold hardiness (e.g., 'Winterbor', 'Lacinato', 'Red Russian').
• Good Drainage: Ensure excellent soil drainage at the planting site to prevent root rot in cold, wet soil.

By precisely timing your planting in late summer/early fall, you give your cold-hardy kale varieties the best possible chance to survive winter and provide a continuous, delicious harvest throughout the colder months.

What kale varieties are best for cold hardiness and overwintering?

Choosing the right kale varieties is paramount for successful cold hardiness and overwintering, as some types are significantly more resilient to freezing temperatures than others. Selecting cultivars specifically bred or known for their resistance to extreme cold will yield the best results and extend your harvest.

Here are the kale varieties best for cold hardiness and overwintering:

1. 'Winterbor' Kale:

   • Characteristics: This is often considered the gold standard for cold hardiness. It's a tall, upright variety with very finely curled, dark blue-green leaves.
   • Cold Tolerance: Exceptionally cold tolerant, reliably surviving into the single digits Fahrenheit (around -10°C to -15°C), and even lower with added protection.
   • Flavor: Maintains excellent flavor and texture in cold, often becoming sweeter after frost.
   • Best For: Reliable overwintering in Zones 5-7 with basic protection, and even Zone 4 with heavy row covers/cold frames.

2. 'Lacinato' Kale (also known as Dinosaur Kale, Tuscan Kale, or Black Kale):

   • Characteristics: Distinctive dark blue-green, heavily textured, bumpy (savoyed), elongated leaves. Often more tender than curly kales.
   • Cold Tolerance: Very good cold hardiness, typically surviving into the low teens Fahrenheit (around -10°C) without much protection, and colder with cover. Benefits significantly from frost sweetening.
   • Flavor: Excellent, rich flavor, often preferred by chefs.
   • Best For: Overwintering in Zones 6-8, and Zone 5 with good protection.

3. 'Red Russian' Kale:

   • Characteristics: Flat, deeply lobed leaves with attractive reddish-purple stems and veins. It offers a unique texture and color.
   • Cold Tolerance: Good cold hardiness, often surviving into the low teens Fahrenheit. Its reddish coloration can intensify with cold, adding aesthetic appeal to the winter garden.
   • Flavor: Tender and sweet, even without a hard frost.
   • Best For: Zones 6-8, and Zone 5 with protection.

4. 'Redbor' Kale:

   • Characteristics: A striking ornamental and edible kale with intensely ruffled, deep purple to red leaves. Very upright growth, providing a strong vertical accent.
   • Cold Tolerance: Excellent cold hardiness, similar to 'Winterbor', with colors becoming even more vibrant and rich in cold temperatures.
   • Best For: Adding dramatic visual appeal and edibility to the winter garden in Zones 5-8.

5. 'Siberian' Kale:

   • Characteristics: Large, broad, slightly frilly leaves, typically blue-green. Known for its extreme cold hardiness.
   • Cold Tolerance: One of the most cold-tolerant varieties, reportedly surviving down to 0°F (-18°C) or even colder, especially under consistent snow cover.
   • Best For: Gardens in very cold climates (Zones 4-6) looking for the most reliable overwintering options.

Tips for Success with Cold-Hardy Varieties:

• Planting Time: Ensure timely fall planting to allow adequate establishment before deep cold sets in.
• Good Drainage: Even the hardiest kale will succumb to root rot in soggy, frozen soil. Ensure excellent drainage.
• Mulch: A thick layer of organic mulch around the base provides extra root insulation.
• Physical Protection: Even these hardy varieties benefit significantly from simple row covers or cold frames in colder zones.

By selecting one of these proven cold-hardy kale varieties, you set yourself up for a successful, prolonged, and delicious winter harvest.

How can physical protection methods extend kale's harvest into winter?

Even the most cold-hardy kale varieties benefit significantly from physical protection methods to ensure successful overwintering and extend their harvest through the coldest months. These methods create a warmer, more stable microclimate around the plants, shielding them from harsh winds, extreme cold, and heavy snow, allowing for continued leaf production.

1. Mulching (Essential Base Layer):

   • Purpose: Insulates the soil and plant crowns from freezing temperatures and protects shallow roots.
   • Method: Apply a thick layer (4-6 inches / 10-15 cm) of organic mulch (e.g., straw, shredded autumn leaves, pine needles) around the base of the kale plants in late fall, before the ground freezes solid.
   • Benefit: Keeps soil temperatures more stable, preventing damaging freeze-thaw cycles that can heave plants out of the ground. This is the simplest and most fundamental protection.

2. Row Covers (Fabric Covers):

   • Purpose: Provides a lightweight, breathable barrier that traps heat and offers crucial protection from light frosts, biting winds, and even some snow.
   • Types: Use a heavyweight (1.5-2 oz/sq yd) floating row cover directly over plants or supported by hoops.
   • Method: Lay the fabric directly over the plants (it's light enough not to crush them) or drape it over garden hoops to create a mini-tunnel. Secure the edges firmly with rocks, soil, or pins to prevent wind from blowing it away and cold air from seeping in.
   • Benefit: Can raise ambient temperatures inside by 5-10°F (3-6°C), extending harvest significantly in Zones 5-7. Allows light and water to penetrate. Easily removed for harvesting.

3. Cold Frames:

   • Purpose: A more substantial, permanent or semi-permanent structure that creates a warm, passive solar microclimate.
   • Construction: A bottomless box (often made of wood, brick, or concrete blocks) with a transparent lid (old window, polycarbonate sheet) that traps solar heat during the day.
   • Method: Build the cold frame over the kale plants. The lid can be propped open on sunny days for ventilation (to prevent overheating) and closed at night or during severe cold spells.
   • Benefit: Provides excellent protection, raising internal temperatures by 10-20°F (6-11°C) or more. Highly effective for continuous winter harvesting in Zones 4-6. Many cold frame kits are available.

4. Cloches / Hotkaps:

   • Purpose: Individual, portable covers for single plants.
   • Types: Can be glass bell jars, plastic domes, or DIY from inverted clear plastic milk jugs (with bottoms cut off and caps removed for ventilation).
   • Pros: Good for protecting small patches or individual plants.
   • Cons: Limited in size, often requires daily venting on sunny days to prevent overheating.
   • Best For: Providing initial protection to newly planted fall kale or for very small harvests.

5. Hoop Houses / Low Tunnels:

   • Purpose: Larger versions of row covers with hoops, suitable for covering entire rows or small beds.
   • Method: Bend flexible pipes (e.g., PVC) or metal hoops over the bed and drape heavy-duty row cover fabric or clear greenhouse plastic over them, securing tightly at the base.
   • Benefit: Offers significant cold protection over larger areas, allowing more plants to overwinter. More internal space than cold frames. Many hoop house kits are available.

6. Snow Cover (Natural Insulation):

   • Purpose: In areas with consistent snowfall, a layer of snow acts as excellent natural insulation, protecting plants from extreme cold.
   • Method: If snow falls on your kale, do not remove it. It provides a protective blanket.

By layering these physical protection methods according to your climate's severity and the specific cold-hardiness of your kale varieties, you can dramatically increase the chances of successfully overwintering kale, providing fresh, sweet greens throughout the coldest months.

How do I harvest overwintered kale to ensure continued production?

Harvesting overwintered kale correctly is crucial to ensure the plant continues to produce fresh leaves throughout the winter and into early spring, rather than succumbing to stress or premature bolting. The "cut-and-come-again" method is key, focusing on sustainable removal rather than stripping the plant.

1. Harvest from the Bottom Up (Cut-and-Come-Again Method):

   • Method: Always harvest the outer, larger, lower leaves first. Use clean, sharp gardening snips or a knife to cut the leaves off cleanly, close to the main stem.
   • Why: This method allows the plant's central growing point (the crown) to remain intact and healthy. The plant continues to produce new leaves from the center, ensuring a continuous harvest.
   • Crucial: Leave at least 4-6 inner, smaller leaves on the plant after each harvest. These inner leaves are vital for the plant to continue photosynthesizing and sustaining itself through the cold.

2. Harvest Selectively, Don't Strip the Plant:

   • Quantity: Only take what you need for a meal or two. Avoid stripping too many leaves from a single plant at once, especially in cold weather, as this can severely stress it and reduce its ability to recover.
   • Frequency: Harvest as needed, perhaps once or twice a week, or less frequently during very cold spells when growth is naturally slow.

3. Harvest on Milder Days (If Possible):

   • Timing: If temperatures are very low, or the plant is frozen solid, avoid harvesting. Harvesting frozen leaves can cause cellular damage to the leaves themselves (leading to mushy texture upon thawing) and can stress the plant.
   • Thawing: Wait for a milder day or for the leaves to thaw naturally. Harvest when the leaves are pliable.

4. Be Gentle with Physical Protection:

   • If using row covers or cold frames, carefully lift or remove them for harvesting to avoid damaging the plants. Replace them securely immediately after harvesting to maintain the protective microclimate.

5. Monitor Plant Health:

   • Regularly inspect your overwintered kale plants. If a plant looks stressed (e.g., yellowing, sparse growth, or appears to be struggling), reduce harvesting from it or stop entirely until it recovers.
   • Remove any yellowed, dead, or mushy leaves (from cold damage or natural senescence) promptly, but be careful not to remove too much healthy foliage.

6. Spring Harvest and Bolting Signal:

   • As spring arrives and temperatures consistently warm up, your overwintered kale will put on a final burst of tender new growth. This is an excellent time for a final, abundant harvest.
   • Bolting: Eventually, as temperatures rise consistently above 70-75°F (21-24°C), the kale plant will "bolt" – send up a tall central flower stalk. This is a natural signal that its life cycle is coming to an end. Once it bolts, leaves will become tougher and more bitter.
   • Final Harvest/Removal: You can still harvest leaves until they become too bitter, or you can allow the plant to flower (which provides food for early pollinators) and then remove it to make way for spring/summer crops.

By diligently following these harvesting practices, you can enjoy a continuous supply of sweet, tender kale throughout the winter, extending your garden's bounty into the leanest months and maximizing the yield from your overwintered plants.