If your cabbage leaves are turning yellow, you’ll want to know the reasons why and how to fix the problem. So read on to find the cause of yellow cabbage leaves along with the solutions.
The most common reasons cabbage leaves turn yellow are due to a lack of sunlight, the temperature being too high, inadequate soil nutrients, watering problems, pest infestations, and some diseases.
Let’s take a look in more detail at each problem and provide solutions so you can fix yellow cabbage leaves to grow a healthy cabbage ready for harvest.
Lack of Sunlight Can Cause Yellow Cabbage Leaves
Insufficient sunlight can lead to your cabbage leaves turning yellow. Although a cool season crop, cabbages thrive in full sun. This means at least 6-8 hours of sunlight a day. If they do not receive adequate sunlight, your cabbage plant won’t be able to photosynthesize correctly and this will turn its leaves yellow.
So choose a sunny spot in the garden to grow your cabbages and make sure they won’t be shaded out by maturing nearby plants you might be growing at the same time.
The Temperature is Too High to Grow Cabbage and Causes Yellow Leaves
Growing cabbage in temperatures that are too high for them will result in yellowing leaves. Higher temperature prevents the cabbage plant from taking up essential soil nutrients and water and the plant will fail to thrive.
Cabbage is a cool-season vegetable and should ideally be grown in temperatures 60-65 °F (15-18 °C). When temperatures exceed 75-80 °F (24-26 °C), cabbage plants will start to yellow, particularly the lower leaves. They’ll also stop growing and likely start to bolt (flower) to finish the plant’s life cycle.
In most climates, it’s a good idea to start growing cabbage in late summer or early fall for a late fall or early winter harvest.
Inadequate Soil Nutrients Cause Cabbage Leaves to Yellow
A lack of soil nutrients can cause yellow cabbage leaves. Cabbage plants need a certain amount of nutrients available from the soil to grow healthy and form lovely big cabbage heads.
If you suspect your soil may be deficient in nutrients, you can add some organic matter to the soil. I love to add homemade compost and aged animal manure before planting cabbage to give them the right start. The addition of organic matter during the growing process is also a good idea.
You can side-dress the soil with compost which is a really gentle and natural way to feed the soil and feed the cabbage plants. A couple of handfuls of compost a few times during the growing season is ideal.
You can also use an organic edible gardening fertilizer like this one to give your cabbage plants a boost and prevent any further yellowing of the leaves.
Although not as common, it’s important to note that too much fertilizer can also turn cabbage leaves yellow, so be sure to read the instructions on the packaging and administer accordingly.
You can also test your soil with one of these soil monitors to find out if you have the right soil pH for growing cabbage. Cabbages prefer a pH of 6-7.
Watering Problems Cause Cabbage Leaves To Yellow
The availability of water is another factor that can cause the leaves of the cabbage plant to turn yellow.
Over-watering is often the most common factor that causes cabbage plant leaves to turn yellow. When you water too much, you can end up ‘drowning’ the plant, which impairs the absorption of soil nutrients and ends up changing the color of the cabbage leaves.
Conversely, not enough water for cabbage plants means they have to consume the nutrients from their healthy leaves. This will turn the cabbage leaves yellow before the leaves completely fall off.
Cabbage prefers consistently moist soil that is neither soggy nor left to dry out. Depending on your climate, watering 2-3 times a week is usually a good rule of thumb.
Pests Can Cause Cabbage Leaves to Yellow
Yellowing cabbage plant leaves followed by stains, holes, eaten edges or veins, and the gathering of bugs are indicators of pests.
Different pests can present numerous visual symptoms, but if the cabbage plant has not been completely taken over, it is possible to contain the pests.
You can also use biological control alternatives, such as ladybug larvae, which feed on pests such as aphids.
In the case of pests for cabbage plants, my recommendation is to keep them protected with netting.
Cabbage Plants Diseases Can Turn Leaves Yellow
There are a few diseases that can cause the leaves of cabbage plants to turn yellow. This often leads to a tweaked leaf which consequently falls off.
To spot cabbage plant disease it’s a good idea to observe your plants regularly. Check your cabbage plants when watering, for example, and you are more likely to catch any problem and take action before it’s too late.
Black Rot Disease
The main symptoms of black rot are characterized by lesions with a yellow halo on the margins of the cabbage leaves. The most common cause is related to contaminated seeds, though the pathogen can spread outside the seeds, and may be active for up to 3 years.
The use of pathogen-free seeds is the most efficient method to prevent the entry of black rot. You should also keep the surrounding garden area free from plant debris and rotate crops.
Alternaria Leaf Spot
Alternaria Leaf Spot results in circular lesions, with a chlorotic halo on the stems and leaves of the cabbage plant. On the head of the cabbage, yellowish spots also appear.
Preventative measures include planting healthy cabbage seeds, practicing crop rotation, and not over-watering cabbage plants. An organic control includes organic fungicides including horticultural neem oil.
Sclerotinia (White Mold)
Sclerotinia rot is caused by the fungus Sclerotinia scletoriorum, which is transmitted through the soil and can survive for long periods on plant debris or in the soil. Most of its life cycle takes place in the soil and this explains why symptoms start on cabbage leaves and parts of the plant in contact with or close to the ground.
The initial symptoms of the disease are like waterlogged lesions on the affected parts, as it causes rot. Usually on stems and branches, presenting as yellowing, wilting, and dryness on the outside of the leaves, which can even lead to cabbage plant death.
Under the attacked areas, the fungus produces a large mass of white, cottony mycelium, a hallmark of the disease. In later stages, it is possible to observe the grayish or black, wart-shaped reproductive structures called sclerotia.
As a form of control, you can use biological control with the Trichoderma fungus like this one applied directly to the soil.