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If you see your cabbage leaves turning yellow, don’t panic! There are a number of potential causes for yellow leaves on your cabbage plant, ranging from simple overwatering to club root or aphid infestation. Cabbage plants are fairly easy to grow, as long as you can keep the butterflies and pigeons off them, but they are susceptible to a few pests and diseases. Plus, like all plants, they need right soil, water, and light conditions.
I grow green cabbage alongside red and white varieties, but it’s the green varieties that I tend to find have the most problems with yellowing leaves. Many of the problems that cause yellow leaves in cabbage plants also affect other cruciferous plants, including cauliflower, Romanesco, and broccoli. Let’s explore some of the key reasons that cabbage leaves turn yellow and what, if anything, you can do about it.
Causes of Cabbage Leaves Turning Yellow
There are many possible reasons why cabbage leaves may be turning yellow, including overwatering, underwatering, environmental stress, lack of sunlight, too hot temperatures, nutrient deficiencies, clubroot, cabbage black rot, and bottom rot.
Overwatering Cabbage
Cabbages are more sensitive to overwatering than underwatering. When cabbages are excessively watered, the leaves can become yellow and wilted due to lack of oxygen reaching the roots. This prevents the plants receiving vital nutrients and can cause the leaves to yellow. It can also create the perfect storm for diseases like clubroot and black rot to set in. When you’re growing cabbage, keep the soil lightly moist, not constantly wet and soggy. Water during dry spells, but not excessively.
If you consistently overwater your cabbage plants, you’ll see yellowing leaves toward the bottom and, as the plant matures, if it survives long enough to form a head, the head will split open down the center, as the cells overhydrate and burst.
Underwatering
Underwatering causes the cabbage leaves to turn yellow due to lack of water and nutrient uptake from the soil. This will also cause them to become wilted, as not enough water is being absorbed by the plant. Cabbage family plants are pretty fussy when it comes to water. They dislike over and underwatering. And unfortunately, the symptoms are essentially the same, at least at first. So check the soil around an inch below the ground to see if it’s wet or dry.
I just stick my finger in and see if it comes away wet or dry, but if you want a more scientific approach, you can use a moisture sensor like this one.
Environmental Stress
Cabbage plants are sensitive to environmental stresses such as high wind and extreme temperatures. These types of stress can cause the leaves to yellow and become wilted. And there’s only so much you can do about these things. The key is good planning. I like to plant my cabbages in a semi-sheltered location that’s away from the worst of the wind. And, if necessary, I can add a temporary wind break during sudden strong winds.
And I try to make sure they aren’t in constant direct sunlight. Instead, I companion plant with taller plants that can provide a little dappled shade, or I plant my cabbage crop in a sheltered but sunny area of my growing space, depending on what my crop rotation needs are for that particular year.
Lack of Sunlight
Cabbages need 6 to 8 hours of direct sunlight each day in order for them to grow healthy and strong. Without enough sunlight, the leaves can turn yellow due to lack of photosynthesis and nutrient absorption. But, interestingly, your cabbage plants will also need some shade to protect them from extreme heat.
Too Hot
Cabbages prefer temperatures in the range of 50 to 75°F (10 to 24°C). When temperatures get too high for too long, it can cause the leaves to yellow and become wilted. If you regularly experience very high temperatures and still want to cultivate cabbage, make sure you provide some shade.
Nitrogen Deficiency
A nitrogen deficiency is the most common nutrient problem in cabbages that causes yellowing leaves. If your cabbage plants are lacking nitrogen, you’ll see the leaves turning yellow from the bottom, up.
Nitrogen is taken up by the roots and moves very slowly throughout the plant. And it’s mobile, so the plant can move the nitrogen where it needs it. So, if there isn’t enough nitrogen in the soil, the growing cabbage moves what nitrogen it does have towards the top, where it’s trying to produce new leaves or nurture the maturing head. And so, the leaves start to turn yellow from the bottom up, as the lower leaves are deprived on nitrogen first.
You can’t turn the yellow leaves green again, but you can provide more nitrogen to save the rest of the plant. And, if you want to be certain that it’s nitrogen deficiency, you can get a simple soil test like this one to check the basic soil nutrient profile. Then add a nitrogen-rich fertilizer, like blood meal or chicken manure pellets.
Club Root
Club root (Plasmodiophora brassicae) is a fungal disease that can cause yellowing in cabbage leaves and other cruciferous plants. Young plants succumb quickly and often die off, but mature plants may survive although will be stunted and may not form a head.
Once this disease takes hold, there’s not much you can do about it. You’ll see that leaves turn a pale yellow and, during hot weather, they wilt. But the leaves recover at night, only to wilt again the following day. This is a telltale sign of club root.
It’s a common issue in wet soils, particularly if the soil also has a low pH. The cabbage plant roots become swollen and stunted, with large, spindle-shaped galls that inhibit water and nutrient uptake.
Cabbage Black Rot
Cabbage black rot, (Xanthomonas campestris), is another fungal disease that affects cabbage plants and causes yellowing of the leaves. It thrives in moist, warm climates and can spread to other plants. If you have infected plants, you’ll notice your cabbage leaves develop V-shaped yellow lesions on the leaf margins. The point of the yellow lesions follow plant veins to the leaf base.
Spreading through water, black rot is one of the most common cabbage diseases that causes yellow leaves. The best way to effectively manage it is to not water excessively and to only water from the base of the plant, so if bacteria is present in the soil, there’s less chance of it splashing up onto the cabbage plants.
If you’ve got black rot in the soil, don’t plant cabbages or related plants in the same place for at least four years. In extreme cases, you may need to sterilize the soil.
Bottom Rot
Bottom rot starts with yellow leaves on cabbage plants, but this quickly progresses to brown, wilted leaves, followed by lower leaves developing sunken black lesions. As the disease progresses, you’ll see brown or black cobweb-like fungal growths appear between the leaves.
In severe infections, the disease spreads up the plant and into the head, but if the disease is milder, it may be confined just to the lower leaves.
Can You Reverse Cabbage Leaves Turning Yellow?
The answer depends on the cause, but generally speaking, no. Once cabbage leaves turn yellow, they can’t be saved. What you can do is try to correct the issue, if it’s a simple fix like consistent watering or nitrogen deficiency. And you can remove the affected leaves. If you identify a disease as the cause of your cabbage leaves turning yellow, then the best option is to remove the infected plants.
How to Prevent Cabbage Leaves Turning Yellow
Now, you can’t always cover every possible scenario, but there are some basic steps you can take to grow the healthiest possible cabbage plants and reduce the likelihood of them getting yellow spots.
Work at building healthy soil. Healthy, balanced soil that plays host to beneficial microorganisms, bacterias, and bugs is the foundation of plant health. Enrich your soil with your own compost and plenty of organic matter. Encourage biodiversity with companion planting and crop rotation. Healthy soil grows healthy plants that are better able to withstand vegetable diseases and insect incursions.
You can test your soil, too, so that you can make any amendments if your soil is lacking any key nutrients.
Be ruthless and only plant healthy cabbages and discard the weaklings.
If you grow cabbage and spot an infected plant and you know it’s a disease rather than a soil, water, or environmental problem, get rid of it. Pull up that plant before the disease spreads through your entire crop.
Practice crop rotation. I can’t tell you how important it is to rotate crops every year. Plant cabbages in a different location every year, and don’t plant them where you had any related plants the previous year. Rotating crops ensures soil health and biodiversity and makes sure if there are any bugs or diseases that favor cabbages laying dormant or overwintering in the soil where you had cabbage plants last year, that there are no more cabbages for them to feast on in the new growing season.
Plant resistant varieties. If you’ve read many of my growing posts, you know I prefer to choose heirloom varieties rather than hybrids. But there are exceptions to the rule. If, for example, you know you have problems with something like clubroot in your area and you can’t sterilize the soil, then if you want to successfully grow brassicas, you’ll need to choose a hybrid variety like Kalibro, Tekila, or Cordesa.
Be smart and use companion planting. It’s a great tactic for improving the quality of your soil, providing extra nitrogen for your cabbages, and discouraging insect pests that are normally drawn to cabbages. And companion planting encourages predatory and beneficial insects, so it has many benefits for growing vegetables of all kinds, not just cabbage.
FAQs
The best way to treat yellow cabbage leaves is to identify the cause. If it’s a lack of nitrogen, over or underwatering, poor soil conditions, too much heat or cold, or not enough sunlight, these things are all easily correctible, and you should still get a good harvest. If, however, you’re growing cabbage plants that are infected with club root, black rot, or another disease, then there’s no real treatment. All you can do is remove the affected plants and hope you’ve caught it before it spreads to the others. Prevention is better than cure.
The most common nutrient deficiency that causes yellow leaves in cabbages is nitrogen. Without enough nitrogen, the plant sacrifices the older, lower leaves and mobilizes the available nitrogen, moving it to the top of the plant to help sustain the newer growth. Calcium and magnesium deficiencies can also cause yellow spotting, or chlorosis on cabbage leaves.
Most types of cabbage prefer full sun but some varieties may need partial shade during certain times of day depending on how hot it gets where you live. Generally speaking though, cabbages do best when planted in well-drained soil that receives at least 6 hours of direct sunlight per day. However, if you regularly get very hot weather with temperatures regularly approaching 90°F (32°C), then you should provide some shade.