How to Grow Heat-Resistant Kale in the City: A Beginner’s Guide
Why Grow Heat-Resistant Kale?
Kale (Brassica oleracea) is a nutrient-dense, hardy green that’s easy to grow in small urban spaces. While traditional kale varieties struggle in the heat, heat-resistant kale varieties allow city gardeners in warmer climates to enjoy fresh, homegrown greens even in the summer months.
Unlike lettuce and spinach, which bolt (go to seed) quickly in warm weather, heat-resistant kale can thrive through higher temperatures, making it a perfect leafy green for summer urban gardens. It grows well in containers, raised beds, and vertical gardens, providing a steady supply of fresh, homegrown greens for months.
This guide will help you successfully grow heat-resistant kale in a small space, from choosing the best variety to harvesting for an extended season.
The Science Behind Heat-Resistant Kale
Kale is part of the Brassicaceae family, also known as the mustard family. This means it’s closely related to other familiar veggies like cabbage, broccoli, cauliflower, and Brussels sprouts. If you’ve grown any of those, you’re already familiar with kale’s plant family and how it grows. Here are some cool things to know about these varieties:
Leaf Structure & Waxy Coating (Cuticle Layer):
Heat-tolerant kale varieties have a thicker cuticle and a natural waxy layer on their leaves. This acts like a shield, reducing water loss through evaporation, called transpiration. That’s why their leaves often feel tougher or shinier.Stomata Control (Tiny Pores on Leaves):
Kale has stomata, tiny openings on the underside of the leaves that help the plant breathe and release moisture. Heat-tolerant types can adjust stomatal opening to conserve water more effectively during hot days, helping the plant stay hydrated.Deep Root Systems:
Some heat-tolerant kale cultivars grow deeper roots, allowing them to access cooler, moister soil layers. This helps them stay hydrated during long hot spells without frequent watering.Anthocyanin & Chlorophyll Density:
The darker green or bluish-black leaves in heat-tolerant kale varieties come from higher concentrations of chlorophyll and anthocyanins, which help protect the plant cells from heat and sun damage. These compounds also give the leaves more nutrients—and sometimes a richer flavor.Delayed Bolting Genes:
Heat-tolerant kale varieties are often selectively bred to resist bolting (flowering too early). This is thanks to specific genes that delay the plant's flowering response, even under stress from heat or longer daylight hours.
Best Heat-Resistant Kale Varieties for Small Spaces
Some kale varieties perform better in hot climates and can handle summer sun without wilting or becoming bitter. Here are three of the best for urban gardeners:
1. ‘Lacinato’ (Dinosaur Kale – Best for Heat Resistance)
Why it’s great: This Italian heirloom is one of the most heat-tolerant kales available, making it a great choice for those living in warmer climates. The dark, bumpy, and slightly waxy leaves help protect from the heat by locking in moisture. While the flavor is mild, there is a surprising sweetness when it is grown in the garden that is absent when purchased from the store. This was the first thing I noticed when I grew it for the first time.
Growth habit: It grows upright and narrow, reaching 2–3 feet tall. They produce long, strap-like leaves ideal for repeated harvests.
Days to maturity: 60–75 days
2. ‘Ethiopian’(mild & tender)
Why it’s great: This Ethiopian variety is slightly less heat-tolerant than the lacinato above, but can still be grown well into the summer in mild climates. It can take temperatures up to 90°F and even tolerate some level of drought. The flavor is mild, slightly sweet, and buttery, making it perfect for cooking or raw dishes.
Growth habit: It grows upright, but the leaves tend to fan out at the top and are large.
Days to maturity: 65-75 days
3. ‘Black Magic’ (SIMILAR to lacinato with mild flavor)
Why it’s great: Lacinato kale is an excellent option for adding greenery to your garden during the hotter months. Its flavor is milder than that of traditional lacinato kale, and it features a long production season. Additionally, it is disease-resistant, making it a great choice for gardeners, especially newbies.
Growth habit: The growth habit is the same as lacinato kale above, upright and narrow, reaching 2–3 feet tall with strap-like leaves.
Days to maturity: 65-75 days
Common Pests and Diseases
While kale is relatively low-maintenance, it can attract a few common pests and diseases like the ones listed below:
Common Pests
Cabbage Worms –Green caterpillars create large holes in leaves. Cabbage white butterflies lay their eggs on the underside of leaves, allowing the larvae direct access to food when they hatch.
Signs: Light green larva sightings and chewed up leaves or no leaves at all.
Solution:
Hand-pick them and destroy them when you see them.
Use row cover fabric on planter boxes, containers, and in-ground beds to keep adult beetles from feeding on young seedlings and laying eggs. Remember to remove the cover when flowers bloom so the plants can be pollinated.
Apply the proper Bacillus thuringiensis (Bt) for cabbage worms. Bt is a naturally occurring bacterium that is toxic to them.
Aphids
Signs: Tiny bugs clustered on leaves, causing yellowing or curling.
Solution:
Prevention and acting early when there is a problem will do wonders for controlling this pest. To control aphids, ensure optimal growing conditions so your kale is as healthy as possible.
When the infestation is small, you can shoot them off with water. Repeat this for a few days until you don’t see them anymore. Doing it in the morning is best so the plant can dry throughout the day.
Encourage natural predators like ladybugs and lacewings to live in your garden.
Flea Beetles
Signs: Sightings of tiny black, bronze, or metallic grey with blue or brown tint beetles that are 1/16”-1/8” long. They feed on leaves and stems, causing tiny holes in leaves and small dents on stems.
Solution: Flea beetles are most active during the spring, and activity usually dies off toward the end of the summer. So, monitor your garden more closely at the beginning of the season and take action quickly if they are present.
Use row cover fabric on planter boxes, containers, and in-ground beds to keep adult beetles from feeding on young seedlings and laying eggs. Remember to remove the cover when flowers bloom so the plants can be pollinated.
Plant or transplant as late as possible if you know you have a problem with flea beetles.
Encourage predatory insects, like parasitic wasps, nematodes, or lacewing larvae, to help you control beetle populations.
Plant a trap crop in the garden that will attract the flea beetles, making them less likely to feed on your kale. The heat-tolerant kale varieties usually have thick, waxy leaves, making them less attractive to flea beetles.
If things get really bad and you have beetles everywhere, use organic insecticides like neem oil to kill them.
Common Diseases
Downy Mildew – This disease is caused by a fungus that primarily affects the plant leaves.
Signs: Yellow or light green blotches on the upper leaf surface, often with a fuzzy gray or purplish mold underneath. Leaves may curl, wilt, and eventually die off.
Solution:
Ensure the plant is healthy and spaced properly when you plant it to promote good airflow. After the kale is established and growing, pruning dead leaves and encouraging vertical growth will also help promote good air flow.
Rotate your crops, meaning don’t plant the same family in the same space every season. This works by disrupting the disease lifecycle and reducing the fungal buildup in the soil.
In very severe cases, use neem oil. Always test on a small piece of the plant and apply before the sun comes out in the morning to prevent burning.
Black Rot – A serious bacterial disease that can harm the brassica family.
Signs: Yellowing, V-shaped lesions with black veining appear on the leaves.
Solution:
Start out with disease-free seeds from a reputable company.
Don’t overwater or handle wet plants. Doing so helps promote the spread of bacterial disease.
Rotate crops on a 3-year cycle.
Remove infected leaves and dispose of them away from the garden.
Powdery Mildew – A white powdery fungus on leaves commonly found in humid environments that spreads easily through wind and rain.
Signs: White powder on leaves and stems that can lead to yellowing or twisted leaves and stunted growth.
Solution:
Keep your garden and tools clean to eliminate and prevent the spread of spores.
Ensure the plant is healthy and spaced properly when you plant it to promote good airflow. After the kale is established and growing, pruning dead leaves and encouraging vertical growth will also help promote good air flow.
Consider growing cultivars, such as lacinato kale, resistant to powdery mildew.
Rotate crops on a 3-year cycle
If you experience an infestation, remove the affected plant and dispose of it in the trash or by burning it.
How to Grow Kale in the Heat
Kale is one of the most beginner-friendly leafy greens you can grow, and with the right heat-tolerant varieties, it can thrive even in late spring and summer. Here's how to set your plants up for success when the temperatures rise.
1. Choosing the Right Container and Setup
Container Size: If you are using a pot, choose one that’s at least 12 inches deep and wide per plant. This gives the roots plenty of room to grow and access nutrients.
Soil: Fill containers with a rich, well-draining potting mix and add compost for a nutrient boost. For raised beds and in-ground planting, mix in compost to boost fertility and moisture retention.
Sunlight: Kale loves 6–8 hours of sun but appreciates a break from intense afternoon heat. Position it where it gets morning sun and some afternoon shade. This is especially important when growing in heat.
Mulch: Add a 1–2 inch layer of straw or shredded leaves around the base to keep the roots cool and reduce evaporation.
2. Growing From Seed
Direct sow seeds outdoors after the last frost, as kale prefers to be planted where it will grow. That being said, you can start them indoors 6-8 weeks before the last frost date to get a head start on your garden. Before transplanting, make sure they are strong and healthy, and the roots are not root-bound to reduce plant shock. We love to use seed starting pots with slits to help the roots air prune as they grow to help develop a healthy root system.
If you are direct sowing, plant 2-3 seeds ½ inch deep in the same hole and space them 12 inches apart. Planting more than one seed per hole helps to increase your chances of germination.
Water gently to keep soil evenly moist until germination (5–10 days). Depending on the temperature, this may need to happen every day to keep the seeds from drying out.
3. Growing from Transplants
If you’re starting with young kale transplants, plant them outdoors once the danger of frost has passed and nighttime temperatures stay above 45°F.
When purchasing young transplants, choose sturdy, healthy plants with green leaves and a well-developed but not root-bound root system to minimize transplant shock. You also want to plant as soon as possible after purchasing your plants.
When you're ready to plant, dig a hole that is slightly larger than the root ball. If necessary, add the appropriate fertilizer to the hole. Place the plant in the hole, ensuring that the roots make good contact with the soil, but be careful not to compact the soil around the plant.
Backfill and cover with mulch.
4. Caring for Your Kale Plants
Once your kale is in the ground and growing, regular care will help it thrive through the heat. The key is consistency—keep the plant healthy and stress-free to reduce the chances of bolting, insect pressure, or disease.
Watering: Kale prefers evenly moist soil, so aim to water when the top inch feels dry. Water early in the morning to reduce evaporation and give the plant time to absorb moisture before the heat of the day sets in.
Fertilizing: Later in the season, you can begin to feed your kale every 2–3 weeks with an organic, nitrogen-rich fertilizer like fish emulsion, compost tea, or worm castings. This keeps the leaves growing strong and vibrant, especially if you frequently harvest.
Providing Shade: In extreme heat, give your kale some relief by using a shade cloth or planting it near taller crops like tomatoes, sunflowers, or corn. This helps reduce leaf stress and prolongs the growing season.
Pest Control: Check your plants weekly for signs of pests like aphids, cabbage worms, or flea beetles. Inspect the undersides of leaves and along stems. If you spot trouble, act early to prevent a full-blown infestation.
Harvesting Kale
When to harvest: Start picking when leaves and stems are 4-6 inches long, about 60 days after planting. You can also start harvesting baby kale when leaves are 2-4 inches long, at around 21 days.
How to harvest: First, cut the plant’s outer leaves, leaving the center intact to allow for continued growth. Avoid harvesting more than one-third of the plant at a time to ensure it continues to thrive. Remember that excessive picking can slow growth, while harvesting the right amount encourages it.
Continuous production: The more you harvest, the more new leaves will grow, keeping your plant productive for months.
Conclusion:
Heat-resistant kale allows urban gardeners in warm climates to enjoy fresh, nutrient-packed greens all spring and summer. With the right variety, proper placement, ample water, and strategic harvesting, you can grow a steady supply of kale for months, even in warmer urban environments.
Whether you use it for salads, smoothies, soups, or sautéed dishes, homegrown kale tastes better and is more nutritious than store-bought greens.
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Happy growing!
With love & gratitude,
Jennifer & Janet
Sources: NIH.org, Science Direct, UMN Extension, UMN Extension
Organic Farming Research Foundation (OFRF_Brassica-Flea-Beetle-Interactive)
