Kale is a hardy and easy plant to grow and great in cool temperatures, making it ideal for fall gardens. But there are some common issues you may run into while trying to grow kale.
Top problems growing kale include discolored leaves, drooping, leaf spots, stunted growth, dying seedlings, legginess, and insect infestations.
By the time you’re through with this article, you’ll be a kale-growing professional—time to get your fingers out of the dirt and onto the mouse for a little research. Let’s learn some stuff!
Kale Leaves Turning Yellow
Yellowing leaves could be a sign of Bacterial Leaf Spot caused by bacterial pathogens (Pseudomonas syringae pv. maculicola) in the Pacific Northwest in daytime temperatures of 65℉ to 75℉ (18.3℃ to 23.8℃) or Xca (Xanthomonas campestris pv. armoraciae) if you live in a Southern state with a hotter climate.
If you’re dealing with the Bacterial leaf spot disease, you’ll first start noticing water-soaked lesions that develop on the kale leaves. As the haloed lesions grow, they merge and start turning yellow. Severe cases will cause the leaves to fall off.
Black rot (Xanthomonas campestris pv. campestris), also known as Xcc, is another condition that starts by turning the leaves yellow. In advanced stages, this pathogen will cause the plant to become black and die. When the problem is Black rot, you’ll notice V-shaped lesions on the edges of the leaves along the veins.
To prevent bacteria such as these from infecting your kale plants, ensure that you’re using heat-treated seeds, which are immune to diseases such as bacterial leaf spot and black rot. Or treat them yourself in hot water heated to 122℉ (50℃ degrees) for 15 minutes.
These types of diseases are frequently transferred from contaminated water, so it’s best to avoid watering your plants with sprinklers. Instead, set up an ebb and flow irrigation. And make sure you’re doing it during the daytime. Avoid watering your plants early in the morning and late at night.
Kale Leaves Drooping
Kale requires cool weather to grow, meaning less than 70℉ (21.1℃). There might be times when a warm spell comes through with fall crops, causing your leaves to droop. If this is the cause of our wilting plants, the leaves should rebound once the weather cools off.
Dehydration can also cause your kale leaves to wilt. They need one to two inches (2.54 cm to 5.08 cm) of water each week. Using a thick layer of mulch around the stalks can help trap water and nutrients into the soil. And you should do regular weeding to keep your plant beds full of nutrition and water.
Fungal diseases can also cause wilting. If you notice small, dark spots appearing, chances are it’s fungal. Treat with a fungicide immediately.
Pests like thrips and aphids can also cause wilting by transferring diseases. Insecticidal soap or neem oil can deter such infestations of these pests as well as other types.
Kale Leaves Turning Purple
If your kale leaves are turning purple, the first thing you should do is make sure you didn’t plant purple kale instead of green kale. If so, the problem is solved.
But if your green leaves are suddenly turning purple, it could be a sign of phosphorus deficiency, as a result of low soil temperatures early in the season. This condition typically affects younger plants.
Purple kale leaves may also be a sign of elevated levels of anthocyanin – a purple-tinted pigment that will build up when your plants aren’t healthy. Cool temperatures, disease, and drought can also cause anthocyanin buildup.
How to Treat Low Phosphorus
To determine if your phosphorus levels are low, use a testing kit such as Soil Savvy’s Soil Test Kit to check the soil. You should also pay attention to the nitrogen, magnesium, and pH levels of the ground, as these crucial nutrients keep your plants healthy.
Using a quality fertilizer mixed to a 10-10-10 ratio of nitrogen-magnesium-phosphorus is a great way to repair the nutritional deficiencies in your soil to repair malnutrition. We recommend using Southern Ag All-Purpose food fertilizer.
Kale Leaves Turning White
Some gardeners have a problem with kale leaves that turn white. One possible reason could be that your plants have white leaf spot caused by fungi Cercospora or Cercosporella spp. White leaf spot causes small circles ¼” to ½” diameter (0.635 cm to 1.27 cm) on the tops of kale leaves.
When left untreated, the spots darken around the border. You may also notice your leaves turning yellow, drying out, and even withering while on the stalk. Protect your plants using a safe fungicide or a copper-inclusive spray. And water your plant below the leaves instead of over the top.
Downy mildew is another condition that can cause white kale leaves. This condition is caused by a fungus called Erysiphe cruciferarum, which grows in white patches on the underside of your leaves, with corresponding yellow spots on the top. Over time, the mold spreads and turns brown in the center. In severe cases, the leaves will turn yellow and die.
To prevent powdery mildew, keep your soil balanced adequately without high levels of nitrogen, rotate your crops every three years with non-susceptible crops, control weeds, and avoid dehydration. Use a fungicide to treat active signs of powdery mildew.
White rust is a condition that can cause your plants to be covered in a white chalky looking dust. On the leaf top, there might be yellow spots. Whereas on the bottom, you’ll see multiple white blisters.
Prevention of white rust includes crop rotation, planting in a well-drained location, and using a fungicide that’s safe for vegetables.
Kale Leaves White Spots
If your kale leaves have masses of small, white spots, you could be dealing with a white blister case caused by the fungus Albugo candida. Multiple strains affect a variety of vegetables, including kale.
You’ll see these white spots on the leaves’ underside, with yellow spots on the top, just like rust or white leaf spot diseases. Your plants are more vulnerable to white blister disease if you live in a climate with 55℉ to 77℉ (13℃ to 25℃) temperatures and in conditions where your leaves will be wet for at least two to three hours (rain, dew, watering).
Unfortunately, there are no fungicides that can treat white blister disease. You will have to use cultural prevention, including rotating crops, providing adequate spacing between plants, and removing and destroying infected plants and weeds.
Frogeye leaf spot is another condition that can cause pale green, gray, or white spots, with a brown ring around the border. This disease comes from the fungus Cercospora brassicicola.
Prevention of Frogeye leaf spot includes having proper soil drainage, planting healthy seeds and transplants, and using proper weeding and crop removal techniques. Crop rotation is also recommended. For the treatment of the condition, use a safe fungicide containing copper, such as Benomyl.
Kale Leaves Black Spots
If you’re noticing black spots on your leaves, there could be multiple reasons. First, you could be dealing with a fungal condition Alternaria Leaf Spot, also called Black Spot or Gray Spot.
This disease causes small dark lesions on the leaves that turn gray or brown. These lesions can be any shape, and they may have a purple-black ring around them. And your leaves will start to brittle and crack with dark brown lesions developing on the stems and petioles in advanced stages.
Black Spot disease is most common in warm, wet weather. You can reduce the chances of your plants getting black spots by using proper spacing between plants, removing cruciferous weeds, rotating crops, and keeping your plant leaves dry during watering. If your plants already have Alternaria leaf spot, treat with a fungicide or copper spray such as Bonide.
Kale Plants Not Growing
If your kale plants don’t seem to be growing, it could be that you’ve planted your garden in the wrong location. Try relocating your plants to a new spot to see if growth improves. In most cases, you’ll want to plant your kale in full sun, but in warm regions, you may want to use an area that offers partial shade, so your plants don’t get sun-scorched.
Other causes of stunted growth in kale plants include improper watering and pH imbalance. Optimal pH levels for growing kale is between 5.5 and 6.8. You can use a home testing kit, such as to test your soil. Limestone is a great additive to reduce acidity in the ground. Sulfur works if you need a higher pH.
Letting your garden become infested with pests and weeds can also cause stunted growth of kale. It’s best to use a natural pesticide or fungicide to treat your plants to prevent infestation. And remove any weeds with gentle pulls at the base of the stalk using your hands. Never try to weed kale using a sharp tool, as kale has shallow roots that can quickly get damaged.
And finally, the final reason your plants could be having weak growth is that you have them planted too close together. Seeds should be planted ½” (1.27 cm) deep with 3″ (7.62 cm) gaps in rows spaced 18″ to 24″ (45.72 cm to 60.96 cm) apart. Once your seeds grow 4″ to 5″ (10.16 cm to 12.7 cm) tall, start thinning your plants to 12″ (30.48 cm) apart.
Kale Seedlings Dying
Dying seedlings can be from multiple problems. If your plants look healthy one day but then suddenly go limp, fall over and die, you’re most likely experiencing an issue called damping off.
Chances are if damping off is your issue, you don’t just lose one or two seedlings but a whole section or even all the plants. You might also notice seeds that don’t come out of the soil, mushy leaves, wilted gray or brown leaves, and stunted roots with grayish-brown sunken spots.
A fungal disease causes Damping-off from wet soil with poor air circulation. Fungi like Rhizoctonia spp, Fusarium spp., and Pythium spp are typically responsible for the damping-off disease.
Planting your seeds in soil that isn’t at an ideal temperature can affect germination (the process of putting down roots and sprouting through the earth). Your soil should be between 70℉ to 75℉ (21℃ to 23.8℃) for your plants to grow correctly.
Too Much Water
Many people think they should douse their seeds with a ton of water so they can grow faster. But too much water can cause your seeds to drown.
Your soil should have a spongy feel to it. It should be damp to the touch but not having water pooling on top of the dirt.
You are dealing with an infestation of fungus gnats if you’re suddenly having a problem with flying insects hovering around the soil of your new plants. These small flies will kill your new plants within seven to ten days.
Fungus gnats usually only occur in plants that are grown in trays or indoors. Plants growing outdoors rarely have fungus gnats as they are prey for larger predatory insects. But you can use beneficial predatory nematodes, which will eliminate fungus gnat larvae.
Kale Seedlings Leggy
A common problem gardeners experience when growing kale from seeds is that as the kale starts to sprout, they become leggy. You end up with pale, thin stems and few leaves. Leggy plants can grow up to have stunted growth, weakened stems, and vulnerable to disease, harsh weather, and pests.
Common causes of leggy plants include insufficient light, overheating, improper watering, and crowding your kale plants too close together. The good news is that it is possible to make your leggy plants fill out and grow up to be healthy.
Seedlings need 12 to 16 hours of light, which is often hard to get when growing your seeds indoors. Artificial light is an excellent substitute for when you’re not able to get enough sunlight.
If you’re growing your plants indoors, keep the temperature regulated between 65℉ to 70℉ (18.3℃ to 21.1℃). And when watering, make sure you’re watering from the bottom up.
Kale Leaves Have Holes
Holes in the plant leaves are a common sign of insect infestation. Aphids, worms, and Harlequin bugs are three common pests that you’ll find feasting on your kale garden.
Cabbage worm infestation, including cabbage worms, diamondback caterpillars, and cabbage loopers, starts appearing in late spring.
They use your kale leaves to lay their eggs, which will quickly hatch into hungry little caterpillars that will feast on your plants. You’ll have the highest number of cabbage worms in late summer and fall.
Aphids are small (less than ¼” or 0.635 cm) soft-bodied insects that multiply quickly. These pests frequently feed on your garden, sucking the nutrients out until your plants are full of holes and short on health.
Other signs of aphid damage include a sticky substance on your plants, and leaves that are turning yellow, curling, or have stunted growth. Aphids frequently transmit diseases to the plants on which they feed.
You’re dealing with a Harlequin Bug if you’re noticing an insect that’s black and orange. These bugs, often referred to as calico bugs, destroy your plants by draining the nutrients, similar to aphids.
Your plants will have open wounds from the feeding, which can allow diseases and other harm to infect your kale. This pest is most common in summer, but they are active year-round in warm climates.
Treatment for Insect Infestation
Using a floating row cover to protect your plants can reduce the chances of pest infestation from all three of these bugs and other types.
Pesticides also work to prevent pest infestations, although not everyone is keen on using chemicals on plants that they will be consuming. Spinosad or Bacillus thuringiensis are excellent insect repellents that are safe for your plants and yourself.
Planting a flower called cleome is a great deterrent for harlequin bugs. You should hand pluck any large bugs you see on your plants at least once a week.
Kale Leaves Turning Light Green
If your kale is taking on a light green color instead of dark green, you could be dealing with a nitrogen deficiency problem. A lack of nitrogen can also cause the leaves to turn yellow. Other nutrients to check include sulfur, iron, and magnesium, which can also cause pale green leaves.
Using a soil testing kit can give you a definitive answer on the soil’s nutrient levels. Be aware that not all soil testing kits test for nitrogen, so you need to carefully read the product description. And using a 10-10-10 fertilizer can correct any problem you’re experiencing with nitrogen.
Kale can be an easy plant to grow in your garden. Armed with the knowledge of potential issues you may face growing kale keeps you prepared to deal with any situation that comes your way. You’re now ready to produce all the kale you can handle. Happy growing.