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Top Problems Growing Cabbage and How to Fix Them

Growing cabbage can be a rewarding experience for amateur gardeners and master farmers alike. It’s important that you have all the information you need about these hardy cruciferous plants to make sure you yield productive crops and healthy vegetables. Although they are generally easy plants to take care of, it’s wise to know what issues you may come across when gardening cabbage.

The top problems people encounter when growing cabbage are vast and varied, but generally include having to deal with issues such as black spots, leaf browning, leaves turning purple, leaves turning yellow, bug infestation, and cabbage looper takeover.

Though these tips may seem daunting, they are easy to resolve. Some of the issues are fungal infections, while others are insect or nutrient based. Armed with information, it’s possible to have a productive and visually pleasing garden that provides food for you and your family. 

Your Cabbage Has Black Spots

When you are shopping at a grocery store and look through the produce aisles, one of the first characteristics you look for when purchasing a head of cabbage is its cleanliness. Most people check around the outer leaves for visual discoloration like patches or spots that look diseased or infected as well as peeking at the inner leaves. 

Even though most commercial produce is clean, it’s possible to come across a head of cabbage that has a rash of black spots that either looks like grime or mildew. Few people want a head of cabbage that looks dirty or moldy – everyone wants good-looking produce, especially if they are growing it in their own garden.

While black spots are commonly found on heads of cabbage that are picked for sale at grocery stores and farmer’s markets and can happen after they are harvested, these spots and patches can also be a result of how the heads of cabbage are grown on personal farms or commercial farms. 

According to a study on cabbage health conducted by a group of botanists in Japan, it was determined that many of the superficial black spots on the interior leaves of heads of cabbage, which were once thought to be caused by low temperatures might actually have been caused by sharp shifts in temperature. These shifts in temperature cause cell death inside of the cabbage, which is why these black speckles present themselves.

This information translates to your home garden by way of regulating the temperature in your own growing space. To combat internal black spots on heads of cabbage, gardeners need to closely monitor the amount of heat and sunlight their plants get. 

If you are growing outdoors, you should make sure that there are ideal conditions for your cabbages. If you are growing indoors, make sure that you have enough warmth and light. Indoor growers have the option of using LED grow lights to make sure their plants are reaching optimal health.

Cabbage grows most easily in cool, temperate climates. Avoid growing cabbage in areas that experience intense shifts in temperature and make sure to give your cabbage plants a moderate amount of light without scorching them. 

Your Cabbage Plants Are Turning Brown

Farmers and gardeners know that browning plants are some of the most upsetting sights in their garden or on their farm. It doesn’t matter whether the crops are swaths of cornfields, a small patch of onions, or even just a pot of flowers – brown spots never bode well for the health of plants.

Especially when growing white plants such as cauliflower, it is disheartening to see splotches of disease on the stems, leaves, and heads of your plants. When your plants start to display signs of browning, you are likely dealing with a strain of fungus. 

Just like when people get fungal infections of the skin, plants can also get infections on the surface of their stems, leaves, and flowers. Just like it’s important to catch infections on your body before they spread, the same applies to plants – make sure that you’re paying close attention to the health of your plants so you can counter infections before they are deadly.

One of the most common issues that growers encounter when they cultivate cabbage is a disease called “downy mildew.” Downy mildew is categorized as a fungal infection that displays first as yellow spots on the top of leaves and which eventually spreads to the underside of the plant and causes brown stains. 

Downy mildew on plants is similar to the mildew that can arise on fabrics, wood, or other organic materials in the home when they are left damp without room to breathe and dry. Mildew tends to break down the integrity of the structure it inhabits, to make sure you catch this illness quickly.

To cure downy mildew, you will likely need to use a fungicide spray. When looking for fungicide, make sure to find one that is safe to use on vegetables since you or someone you know will be eating the cabbage eventually. An example of a fungicide that’s safe to use on edible plants is Southern Ag Liquid Copper

You will need to focus on spraying the plants that are the most affected by the fungus and to spray any other plants that may have been exposed to downy mildew. Make sure to follow the instructions on the bottle and to rinse your cabbage thoroughly before eating.

Another fungal infection that may be affecting your cabbage plants is called “Alternaria leaf spot.” Though it is like downy mildew in that it causes brown spots on your cabbage plants, it is unique in its shape and appearance. Downy mildew causes broad speckled patches on the leaves of your cabbage plants while Alternaria appears as distinct circular spots. The same fungicide used for downy mildew can also be used for Alternaria leaf spot.

To prevent brown spots in the future, be careful to dispose of and segregate infected plants after harvesting. What’s unfortunate about fungal plant infections is that they have a tendency to move from one plant to another with ease. Focus on watering the base of the plant instead of the leaves. It’s also important to remember to keep your cabbage plants out of swampy or shady areas and to give them an adequate amount of sunlight. 

Your Cabbage Is Turning Purple

Red (purple) cabbage is a naturally occurring variety of the plant that is highly nutritious and produces a bright natural dye. It has a distinct color that adds variety and nutrition to salads. 

However, if you are growing exclusively green cabbage, there is a reason for concern when your plants start to turn purple. When green cabbage plants begin to turn purple, you may be dealing with a nutritional deficiency of the soil you’ve used for planting, as well as poor root health.

Soil nutrient levels are one of the secrets to healthy plant growth that many amateur growers forget to consider when they start their gardens or crops. This is a factor in gardening that many people do not consider because they have no knowledge of it, or they have not been informed. Though soil may visually appear moist and healthy, it may have been depleted of nutrients by previous gardens or crops having been grown in that area.

The first step to determining how to remedy the issue of plants turning purple is to test the soil for nutrient density. Much like taking a blood test at a doctor’s office for nutrient levels in the human body, it’s a simple process to test soil for its nutritional contents to see where your crops might be lacking. 

An easy way to determine soil health is to use an at-home test like this one: the MySoil Soil Test Kit. These kits are designed for you to be able to determine the quality of your soil without having to consult an expert.

It’s believed that a specific purple tint to plants could be caused by a phosphorus deficiency in the soil. If your soil quality test results show that your soil is lacking in phosphorus, you will need to supplement with a fertilizer like Burpee Organic Bone Meal

Oftentimes using bone meal supplements in your garden is as easy as sprinkling a powder on and around your plants, but each product has its own instructions, so make sure to follow them clearly. Here is a video that gives you some insight into how important phosphorus is for plant growth.

Your Cabbage Is Turning Yellow

As mentioned in the last section, the two main colors of cabbage that modern gardeners grow are purple and green. Purple cabbage tends to keep its naturally bright color, while green cabbage can sometimes turn a yellow shade. When your cabbage plants begin to turn yellow, you should be concerned. The yellowing of cabbage plants is not natural and can affect the texture, flavor, and nutritional value of what is generally a healthful plant.

Yellowing of cabbage plants is generally caused by a condition called “yellows,” or Fusarium wilt. Yellows has been occurring for a long time in the United States and is one of the most common diseases in cruciferous plants. This disease presents itself as the gradual yellowing of the lower leaves of cabbage plants. 

You will know that you have a case of Fusarium wilt when your cabbage leaves start becoming pale yellow with brown spots. If not treated properly, yellows could take over the plant, and the whole head of cabbage may be lost.

According to botanists at Cornell University, yellows cannot be prevented without completely changing the species of cabbage you use. Because Fusarium wilt can survive in the soil for a long time, even if you’ve never planted cabbage before, if yellow fungus lives in the soil on your property, your plants are likely to suffer.

The best way to prevent Fusarium wilt in the future is to plant resistant crops. The Cornell botanists give examples of fungus-resistant cabbage species, including Green Boy, Superette, and Empire Danish varieties. If your cabbage plants are suffering from yellows, you will have to harvest them before they get taken over.

Even though it might be disappointing, this experience with Fusarium wilt will give you the experience you need to overcome your next case of plant illness and prevent it from happening again in the future. Use these experiences to plot out your garden more effectively next season – it’s never too early to start envisioning a more ideal garden plot. 

There Are Bugs on Your Cabbage

Few things are as discomforting as having to pick worms off your freshly harvested cabbage plants. Especially since cabbage is served raw, you need to be very mindful of little critters attaching themselves to your plants.

Getting rid of pests from your cabbage plants can be difficult and frustrating. One of the most common pests that turn cabbage plants into their lunches are cabbage worms. These little worms can be identified by their bright green color that tends to blend into the leaves of your cabbage plants. It’s important to look closely at both the upper and lower sides of your cabbage plants when checking them for infections and infestations.

These cabbage worms tend to eat all the fresh green matter on your plants and leave behind what looks like a skeleton of your cabbage plants. Cabbage worms have the potential to ruin an entire crop as they consume everything except the veins and stems of plants. Because of this, it’s important to make sure that they are taken care of before they have the potential to spoil your crops or plots.

To get rid of cabbage worms that have taken over your plants, you will need to use an effective yet vegetable-safe insecticide. Much like applying a fungicide, you will have to pay close attention to the instructions on the package and make sure it can be used on vegetables. A pesticide spray that is easy to use and affordable is Monterey B.t. Spray. Here is a helpful video that can show you how to apply the spray to your plants.

Your Cabbage Is Infested With Loopers and Moths

Much like cabbage worms, cabbage loopers are one of the most common pests that like to make a snack out of your cabbage plants. Loopers can be found on a variety of crunchy green plants, particularly those like cabbage, broccoli, and lettuces. These worms look like little inch worms that crawl across the leaves of your cabbage plants and feast on them for lunch.

Cabbage loopers are the larvae of the owlet moth, a small powdery grey moth that lurks around gardens and crops. When the moths are in the larvae (worm) stage, they host themselves on cabbage plants and use them as a source of food. When in the larvae stage, owlet moth babies look like cabbage worms but with a lighter color and fewer legs. These larvae can also use the cabbage plants as cocoon hosts so they can morph into fully-grown moths.

To get rid of cabbage loopers, you will want to use the same method as mentioned above for cabbage worms. An insecticide that is effective and vegetable-safe is the best way to get rid of cabbage loopers. 

Bacillus thuringiensis is a naturally occurring bacteria that is toxic to looper larvae, so by spraying it or sprinkling it on your crops, you can eliminate the larvae from your cabbage. A B.t.-based insecticide will help you control and mitigate the population of cabbage loopers on your plants and will help keep your cabbage in mint condition.

When these cabbage loopers are given enough free rein to grow into moths, then the problem becomes a bit trickier. An easy and simple way to prevent moths from getting into/onto your plants is by covering them up. To cover your plants, you will need some sort of mesh structure to act as a breathable roof over your garden beds or rows. This video will help you figure out some of the easiest ways to build a cover for your raised garden beds.

Make sure that, when you are constructing the covers for your garden beds, that you are choosing the correct material – plastic for the winter to insulate the plants, or mesh for the summer for more breathability.

Final Thoughts

Cabbage plants are easy to grow for most people, but there are several difficult issues you may encounter. Such issues include your cabbage plants turning unnatural colors. If you have black spots, brown patches, or purple discoloration, you are likely dealing with either a fungal infection or a lack of nutrients in the soil.

If you are dealing with a pest infestation on your plants, there are a few insecticides on the market that are organic and safe to use on vegetables. Just make sure you read and follow the instructions on the package as they are written.

With these tips and solutions, you are likely to be able to cultivate healthy, nutritious, and delicious cabbage in your home garden.

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