What are the signs of kale in summer? - Plant Care Guide

The signs of kale in summer often indicate stress, as kale is primarily a cool-season crop that struggles in intense heat. These signs include bolting (sending up a flower stalk), bitter-tasting leaves, stunted growth, yellowing foliage, and an increased susceptibility to pests like cabbage worms and aphids. Recognizing these symptoms helps gardeners understand that their kale is likely suffering from summer heat and adjust care accordingly.

Why Does Kale Struggle in Summer Heat?

Kale struggles in summer heat because it is fundamentally a cool-season vegetable, a member of the Brassica oleracea family (along with broccoli, cabbage, and cauliflower) that thrives in milder temperatures. Its physiology is simply not adapted to prolonged periods of high heat and intense sun, leading to various forms of stress and decline.

Here's why summer heat is problematic for kale:

1. Bolting (Premature Flowering):
   • Primary Issue: High temperatures are the main trigger for bolting. When kale is exposed to sustained temperatures above 75-80°F (24-27°C), it interprets this as a signal that its growing season is ending. As a survival mechanism, it rapidly switches from producing leafy greens to developing a flower stalk and seeds.
   • Consequence: Once kale bolts, its energy is diverted to reproduction, leading to a significant decrease in leaf production and quality.
2. Bitter Flavor and Tough Texture:
   • Flavor Change: As kale bolts or experiences heat stress, its leaves produce more glucosinolates (sulfur-containing compounds that give brassicas their distinctive flavor). While present naturally, stress increases their concentration, leading to a much harsher, more bitter taste.
   • Texture Change: The leaves also become tougher, stringier, and less palatable, losing their tender, crisp texture.
3. Stunted Growth:
   • High temperatures can inhibit kale's overall growth. Instead of forming lush, expansive leaves, the plant may appear stunted or spindly, putting its energy into survival rather than robust development.
4. Increased Water Stress:
   • High temperatures lead to increased transpiration (water loss from leaves) and rapid evaporation from the soil. Kale, needing consistent moisture, quickly becomes water-stressed, which exacerbates other heat-related problems.
5. Pest Proliferation:
   • Warm summer temperatures create ideal breeding conditions for many common kale pests, such as cabbage worms (cabbage loopers and imported cabbageworms), aphids, and flea beetles. Stressed plants are also less able to defend themselves, making them more susceptible to heavy infestations.
6. Disease Susceptibility:
   • While not always direct, heat stress can weaken kale plants, making them more vulnerable to certain fungal diseases (e.g., powdery mildew) if humidity is also high, or if they are otherwise compromised.

In essence, summer heat acts as a powerful environmental signal to kale, pushing it towards an early reproductive phase and significantly degrading the quality of its edible leaves, making it a challenging crop to grow in the peak of summer.

What are the Visual Signs of Kale Bolting in Summer?

Bolting is the most definitive visual sign of kale struggling in summer heat, signaling that the plant is attempting to reproduce rather than continue producing edible leaves. Recognizing these changes early can help you understand why your kale is declining.

Here are the visual signs of kale bolting in summer:

1. Elongated Central Stalk:
   • The most obvious sign is the rapid upward growth of a tall, woody central stalk from the center of the kale plant. This stalk grows much taller than the leafy part of the plant.
2. Smaller, Spaced-Out Leaves on Stalk:
   • As the stalk elongates, the leaves growing on it will be noticeably smaller, narrower, and more widely spaced than the large, lush leaves you harvest from the main plant.
3. Formation of Flower Buds:
   • At the top of the elongated stalk, you'll see clusters of small, tightly packed flower buds. These buds are typically yellowish-green, resembling miniature broccoli florets.
4. Yellow or White Flowers:
   • If left to continue, these buds will open into small, four-petaled yellow or white flowers, characteristic of the Brassica family.
5. Overall Spindly Appearance:
   • The entire plant might look less robust and more spindly or gangly as its energy shifts from developing dense foliage to producing the flower stalk.
6. Reduced Leaf Production and Quality:
   • You'll notice a significant decrease in the production of new, tender leaves from the base of the plant. The existing leaves may also become tougher and less appealing visually.

Once kale begins to bolt, the quality of its leaves for eating will rapidly decline, becoming bitter and fibrous. While you can often pinch off flower stalks to briefly delay the process, the plant is signaling its physiological response to prolonged heat, and the bitterness will likely remain.

How Does Summer Heat Affect Kale's Flavor and Texture?

Summer heat directly and negatively affects kale's flavor and texture, transforming its desirable qualities into less palatable ones. This change is a physiological response to stress and a natural part of the plant's life cycle.

Here's how summer heat impacts kale:

1. Increased Bitterness (Flavor):
   • Chemical Change: High temperatures, especially those that trigger bolting, cause kale to produce a higher concentration of glucosinolates. These are sulfur-containing organic compounds that contribute to the pungent, slightly bitter flavor characteristic of brassicas. In cool weather, their levels are balanced, providing a pleasant earthy taste. In heat, their concentration intensifies, leading to a much harsher, intensely bitter flavor.
   • Defense Mechanism: This increase in bitterness is also a plant's defense mechanism, making it less appealing to herbivores when it's stressed and trying to set seed.
2. Tougher, Fibrous Texture:
   • Rapid Growth/Woodiness: As kale begins to bolt, the plant puts energy into elongating its central stalk and developing reproductive structures. The stems and veins in the leaves become more fibrous and woody.
   • Less Tender: The leaves themselves become thicker, coarser, and less tender than those grown in cool conditions. They lose their desirable crispness and succulence, making them less enjoyable raw or even cooked.
3. Reduced Sucrose Content:
   • In cooler temperatures, kale (like many leafy greens) accumulates sugars (sucrose), which gives it a slightly sweeter, milder flavor. Heat stress can disrupt this process, reducing sugar production and further contributing to the perceived bitterness.
4. Smaller Leaves:
   • While not strictly a texture/flavor issue, kale under heat stress tends to produce smaller, less robust leaves compared to the expansive, tender leaves of cool-season growth.

In summary, summer heat acts as a switch, telling the kale plant to prepare for reproduction. This shift in physiological priorities fundamentally alters the chemical composition and physical structure of the leaves, making them bitter and tough, and far less enjoyable for culinary use.

What Pests Are More Prevalent on Kale in Summer?

When kale struggles in summer, it often becomes a magnet for certain pests that are more prevalent in warmer weather. These pests, combined with the plant's stress, can quickly devastate a summer kale crop.

Here are the pests most likely to plague kale in summer:

1. Cabbage Worms (Cabbage Loopers and Imported Cabbageworms):
   • Appearance:
     • Cabbage Looper: Green caterpillar that "loops" its body as it crawls.
     • Imported Cabbageworm: Velvety green caterpillar that is often found on the underside of leaves.
     • Damage: Irregular holes chewed through leaves, sometimes large sections. You'll also see their green-brown frass (excrement) on the leaves.
   • Activity: Butterflies (white cabbage moths and brownish loopers moths) lay eggs on kale leaves, which hatch into these voracious caterpillars. Their populations explode in warm weather.
   • Control: Hand-picking, using BT (Bacillus thuringiensis) spray (an organic caterpillar killer), or covering with floating row covers.
2. Aphids:
   • Appearance: Small, pear-shaped insects (green, black, or gray) clustered on the undersides of leaves and on new growth. They reproduce rapidly in warm conditions.
   • Damage: Sucking sap causes distorted, curled, or yellowing leaves. Can excrete sticky "honeydew," leading to sooty mold.
   • Control: Strong spray of water, insecticidal soap, or introducing beneficial insects (ladybugs).
3. Flea Beetles:
   • Appearance: Tiny (1/16 inch), dark, jumping beetles that resemble fleas.
   • Damage: Chew numerous small, round holes ("shot-hole" appearance) in leaves. This is particularly damaging to young plants.
   • Activity: More active in warm, dry weather.
   • Control: Floating row covers are effective. Dusting with diatomaceous earth.
4. Harlequin Bugs:
   • Appearance: Stink bug relatives with distinctive black and orange or black and red markings.
   • Damage: Pierce leaves and suck out sap, leaving behind white or yellow spots. Heavy feeding causes wilting and plant death.
   • Activity: Active in warm temperatures, especially in the Southeast.
   • Control: Hand-picking, removing egg clusters, maintaining garden hygiene.
5. Slugs and Snails:
   • Appearance: Slimy trails on leaves and soil.
   • Damage: Chew large, irregular holes in leaves, especially at night.
   • Activity: Thrive in humid summer conditions, especially after rain or heavy irrigation.
   • Control: Hand-picking, beer traps, slug baits (organic options available).

Protecting kale from intense summer sun and ensuring consistent moisture can help reduce stress, making it slightly more resilient to these common summer pests.

What Are Some Strategies to Help Kale Survive Summer?

While kale prefers cool weather, there are several strategies to help kale survive summer and potentially extend its harvest, especially in regions with milder summers. These methods aim to mitigate the effects of heat and sun stress.

1. Choose Heat-Tolerant Varieties:
   • Some kale varieties are more tolerant of heat and slower to bolt. Look for varieties marketed as "heat-tolerant" or "slow-bolting."
   • Examples: 'Lacinato' (Dinosaur) kale tends to handle heat better than some curly varieties. 'Red Russian' kale also has some heat tolerance. Research heat-tolerant kale varieties.
2. Provide Afternoon Shade:
   • Location: Plant kale in a spot that receives afternoon shade (from a building, fence, or taller plants). Morning sun is beneficial, but the intense afternoon sun (especially from 1 PM to 4 PM) is what often triggers bolting and bitterness.
   • Shade Cloth: If no natural shade is available, install a garden shade cloth over your kale during the hottest parts of the day or throughout the summer. This can reduce temperatures by 10-15°F (5-8°C).
3. Consistent and Adequate Watering:
   • Deep Watering: Kale needs consistent moisture to cope with heat. Water deeply and regularly, ensuring the soil remains evenly moist but not waterlogged.
   • Avoid Drought Stress: Periods of drought stress followed by heavy watering can trigger bolting and bitterness. Use a soil moisture meter to maintain consistent moisture.
   • Morning Watering: Water in the early morning to allow leaves to dry before the heat of the day, reducing fungal issues.
4. Apply Thick Mulch:
   • Apply a 2-4 inch layer of organic mulch (e.g., straw, shredded leaves, wood chips) around the base of kale plants.
   • Benefits: Mulch helps to keep the soil cooler, conserves soil moisture by reducing evaporation, and suppresses weeds that compete for water.
5. Pest Management (Proactive):
   • Floating Row Covers: To physically exclude common summer pests like cabbage worms and flea beetles, cover your kale plants with floating row covers from the moment of planting. Ensure the edges are sealed to prevent pest entry.
   • Regular Inspection and Treatment: Frequently inspect plants for pests and hand-pick caterpillars. Use organic sprays (e.g., neem oil, insecticidal soap, BT for caterpillars) as needed.
6. Harvest Regularly:
   • Even if the quality isn't peak, regular harvesting of outer leaves can sometimes delay bolting slightly by signaling to the plant to continue vegetative growth. Harvest young, tender leaves before they become too bitter.
7. Fertilize Adequately:
   • Ensure the plant has enough nutrients to support growth, but avoid excessive nitrogen which can encourage lush growth that's more vulnerable to pests. Use a balanced vegetable fertilizer.

While these strategies can help, understand that in very hot climates, it might be more practical to treat summer as an "off-season" for kale and focus on planting successions in spring and fall.

Can I Plant Kale in Summer for a Fall Harvest?

Yes, you can absolutely plant kale in summer for a fall harvest, and this is often the most successful strategy for growing kale in many regions of the USA. Starting kale in late summer allows it to establish during warmer days, then thrive as temperatures cool, leading to a sweet and tender harvest in autumn and often into winter.

Here's why and how to do it:

1. Optimal Timing (Succession Planting):
   • When to Plant: Plant kale seeds or transplants in mid-to-late summer, usually 8-10 weeks before your average first fall frost date. This typically means July or August for most temperate zones.
   • Why it Works: The young seedlings get a warm start but mature as temperatures begin to cool. Kale thrives in cooler temperatures and can even tolerate light frosts, which sweeten its flavor.
2. Benefits of Fall Kale:
   • Improved Flavor: The onset of cooler weather and light frosts converts starches in kale leaves into sugars, resulting in a sweeter, milder, and more tender flavor than summer-grown kale. This is often when kale is at its culinary peak.
   • Reduced Pest Pressure: Many common kale pests (like cabbage worms and aphids) start to decline in activity as temperatures cool in fall, naturally reducing pest pressure.
   • Less Bolting: The decreasing temperatures and shorter daylight hours of fall reduce the risk of bolting, allowing the plant to focus its energy on producing lush leaves.
   • Extended Harvest: Depending on your USDA hardiness zone, fall-planted kale can provide harvests from autumn often through early winter, and sometimes even survive under snow cover.
3. Planting Methods for Fall Kale:
   • Direct Sowing or Transplants: You can directly sow kale seeds into well-prepared soil, or start seeds indoors 4-6 weeks before your desired outdoor planting date to get a jump start with transplants.
   • Site Selection: Choose a location with full sun to partial sun.
   • Soil Preparation: Amend the soil with plenty of compost to ensure good fertility and drainage.
   • Watering: Ensure consistent moisture during the establishment phase (when it's still warm), then adjust watering frequency as temperatures cool.
4. Summer Care for Fall Starts:
   • If you're planting in the heat of summer for a fall harvest, you may still need to provide temporary afternoon shade (e.g., with shade cloth) for the young seedlings to help them cope with initial heat stress.
   • Ensure consistent watering to prevent wilting during hot spells.
5. Winter Protection (for extended harvest):
   • In colder zones, to extend your fall harvest well into winter, consider covering your kale with floating row covers or even a cold frame or low tunnel when hard freezes are predicted. This protects the leaves from severe frost damage.

Planting kale in summer for a fall harvest is a highly recommended strategy that leverages the plant's natural preference for cooler weather, yielding superior flavor and a longer harvest period.

What Are Ideal Growing Conditions for Kale to Produce its Best Flavor?

To ensure kale produces its best flavor, you need to cultivate it under conditions that minimize bitterness and toughness, promoting sweet, tender leaves. This primarily means providing the cool temperatures that the plant naturally prefers.

Here are the ideal growing conditions for kale to produce its best flavor:

1. Temperature: Cool and Crisp (60-75°F / 15-24°C daytime)
   • Optimal Range: Kale truly shines when grown in cool to mild temperatures. This is the range where its flavor is sweetest and its texture is most tender.
   • Frost Sweetening: The best flavor is often achieved after the plant has experienced a light frost or two (temperatures dipping to just below freezing, around 28-32°F / -2 to 0°C). The cold causes the plant to convert starches into sugars, leading to a noticeable increase in sweetness and a reduction in bitterness.
   • Avoid Heat: Prolonged temperatures above 80°F (27°C) will inevitably lead to bitterness and toughness.
2. Sunlight: Full Sun to Partial Shade:
   • Full Sun: Kale prefers full sun (at least 6 hours of direct sunlight) for optimal growth and nutrient development during cool seasons.
   • Partial Shade in Summer: If attempting to grow kale into warmer periods, providing afternoon shade is crucial to protect it from intense sun and heat, which helps reduce bitterness and bolting.
3. Soil: Rich, Well-Draining, and Fertile:
   • Organic Matter: Kale is a heavy feeder and thrives in nutrient-rich soil amended generously with compost or aged manure. This provides a steady supply of nutrients for lush leaf growth.
   • Good Drainage: While needing consistent moisture, the soil must be well-draining to prevent waterlogging, which can stress the plant and affect flavor.
   • pH: Kale prefers a slightly acidic to neutral soil pH, typically between 6.0 and 7.0.
4. Moisture: Consistent and Even:
   • No Stress: Consistent moisture is vital. Drought stress can lead to tough, bitter leaves and trigger premature bolting. Keep the soil evenly moist, especially during dry spells.
   • Avoid Overwatering: Don't let the soil become waterlogged, as this can lead to root issues. A soil moisture meter can help maintain consistency.
5. Fertilization: Balanced Nutrients:
   • Provide a balanced vegetable fertilizer during the growing season to support vigorous leaf production. Ensure adequate nitrogen for leafy growth, but a good balance prevents excessive bitterness. A general vegetable fertilizer works well.
6. Pest Control:
   • Healthy, unstressed plants with good pest control will produce better-tasting leaves free from damage. Pest stress can also contribute to bitterness.

By prioritizing cool temperatures, consistent moisture, and nutrient-rich soil, you can cultivate kale that is exceptionally tender and flavorful, truly showcasing its culinary potential.