Grow Your Best Cabbage: How to Prevent Pest Damage, Disease, and Other Problems
Apparently, cabbage has this reputation for being difficult to grow. But really, it’s a hardy and reliable crop, and it’s less prone to bolting than some of the other brassicas like broccoli and cauliflower.
Turns out, some of the worst cabbage problems that can cause total crop loss are easy to avoid with the right approach. As long as you take some steps at planting time to set things up for success, you’ll have some nice heads of cabbage to harvest in spring or fall.
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Pests: The Biggest Cabbage Problem
At this point, I’m convinced the reason why people say cabbage is hard to grow is the pest pressure! Cabbage plants are a prime target for two incredibly destructive pests, in particular.
I see sooo many social media posts of hole-riddled cabbage plants, with desperate gardeners asking what can be done. Those holes are the work of the cabbage looper and/or the imported cabbage worm.
Both of the above caterpillars will reduce your lush cabbage plants to absolute swiss cheese in a matter of days. They’ll tunnel into the heads once they’re done with the outer leaves, leaving them riddled with mushy tunnels full of caterpillar poo (i.e. totally inedible, unless you’re just really determined).
Folks will recommend a number of natural control methods for these things, from spraying with Bt (Bacillus Thuringiensis) to hand-picking. Both of those methods do work, but a lot of gardeners get burned out and let it slide. Understandably, because they can be overwhelmingly time-consuming.
Hand-picking will be an ENDLESS job, in places with high cabbage worm pressure. Bt needs to be re-applied weekly or every time it rains. I’ve heard some gardeners who wanted to stay organic admit they’ve resorted to toxic pesticides like pyrethroids to protect their cabbages.
Thankfully, the cabbage worm problem has a simple, natural, and low-effort solution. To grow cabbage without using toxic pesticides or being angry all the time, you have to net those babies!
Netting For Cabbage Worm Control
Cabbage-eating caterpillars are the larval stage of a moth (cabbage looper) or a butterfly called a cabbage white (imported cabbage worm). The moths and cabbage whites lay their eggs all over your cabbages, which then hatch into the hungry larvae. Fine-mesh insect netting creates a barrier the moths/butterflies can’t get past to lay those eggs, and it’s about 100% effective at preventing a caterpillar invasion.
Garden insect netting comes in a variety of size options and quality grades. The nice stuff from greenhouse supply stores can be a little pricy, but the cheaper options work perfectly fine. We got budget netting for our garden, and it’s lasted us a number of seasons so far. It’s a little more prone to holes, but you can patch it up with screen repair tape as needed.
Whatever kind of support structure you come up with will work to hang your netting, since it’s quite lightweight. We went the hoop-tunnel route and made our hoops with ¾ inch PVC conduit fitted over rebar stakes. If you grow in raised beds, you can fasten pipe clamps on either side to hold the hoops in place.
After you hang the netting, make sure it’s weighted down well on all sides to prevent any butterfly or moth from finding its way underneath. Use boards, T-posts, rocks, or whatever you have around. Some cheap greenhouse clips work great with the PVC for extra security.
Guess how many cabbage worms we’ve picked off our cabbage plants since we started using netting? Zero! We still get some slug damage on the lower leaves, but not one cabbage caterpillar.
Getting your netting and materials for a support structure is a small one-time investment. But pesticides like Bt are pretty expensive, so it’ll pay for itself. Not to mention, it’s well worth the peace of mind knowing your cabbages aren’t being decimated by worms if you go on a weekend vacation!
Other Cabbage Pests
A few other bad guys that might come for your cabbages are slugs, cabbage root flies, and other nuisance caterpillars like armyworms and cutworms.
Armyworms and Cutworms
Unlike cabbage caterpillars, which hatch from eggs laid directly on the plants, armyworms hatch out by the hundreds from randomly placed egg clusters. They’ll then spread out like an invading army to find food (hence, armyworms).
These things are smaller than a grain of rice when they first hatch out, and we’ve had them breach our netting from time to time. Fortunately, they don’t do near as much damage to brassica crops as cabbage worms do. I usually just pick off any I see whenever I lift the netting up for weeding or fertilizing.
Cutworms are mostly a danger for seedlings, since they like to chew through the stem base like a beaver felling a tree. If you know these caterpillars are around, you can collar seedlings with a slice from a paper towel of toilet paper roll to protect the stems.
Slugs
Invasive garden slugs are an aggravating and persistent pest that won’t be deterred by insect netting. Those jerks will go right under it. And boy, do they LOVE cabbage.
Slugs cause the most issues for cabbage seedlings. Once the plants get larger, the slugs typically stick to munching on the lowest leaves, which won’t really hurt the plant. To protect young cabbage seedings from slugs, you can surround them with Diatomaceous Earth, set beer traps, or put out iron phosphate bait.
If you have a serious slug problem, check your seedlings during wet weather and in the evenings/mornings to remove any slugs that get past your prevention measures.
Here are a few more tips for dealing with a slug invasion: Controlling Slugs in the Garden: 5 Natural Methods That Actually Work.
Cabbage Root Flies
These gross little maggots set about eating your cabbage plants’ roots after the adult fly lays her eggs at the base of the plant. They’re pretty destructive, and their feeding can stunt your plants’ growth and cause symptoms of nutrient deficiency, like purpling or yellow leaves.
If you suspect cabbage root flies, you can scrape some soil back to expose the roots. You’ll be able to see the tiny white maggots. There’s not a ton you can do once you’ve got an infestation, but netting will keep most of the flies out with your next crop. If you have a problem with root flies, don’t plant cabbage in the same spot next year.
Cabbage Plant Diseases
In our garden, we don’t see disease problems on cabbage near as much as on things like tomatoes and cucumbers. Cabbages can get a few different diseases, though, the most problematic of which are black rot, downy mildew, club root, and fusarium yellows.
Fusarium Yellows
Fusarium, or cabbage yellows, is a soil-borne fungal disease that begins in the roots and causes dieback starting on lower leaves. This dieback will often appear first on one just one side of the plant. It’s usually a non-salvageable situation. However, in fall-planted cabbages, the plants might sometimes recover once cool temps arrive, since the fungus doesn’t thrive below 72 degrees.
Fusarium often strikes at random, often affecting just one or two plants in a given season. This fungus can survive in the soil for a long time. If you have repeat problems with mysterious lopsided dieback, consider not planting brassicas like cabbage in that part of the garden for a while.
Black Rot
Black rot is a bacterial disease that causes leaf lesions and, in some cases, rotting of the cabbage head. V-shaped lesions on the outer edges of leaves are the classic symptom of black rot. Black rot doesn’t always spread to the cabbage head; sometimes, you can remove infected leaves early on and save the plant.
Black rot is specifically a disease of brassicas, not a common and widespread pathogen like your garden-variety tomato blights, so it most commonly ends up in gardens via infected seeds. Make sure you get your cabbage seeds or seedlings from a reputable source.
Downy Mildew
Downy mildew is an oomycete, or water-mold, that causes leaf spots and leaf dieback in cabbage. You’ll see irregularly-shaped dead spots on the leaves. Sometimes, you might see a gray or white mold on the underside of the leaves, or black spores within the lesions.
Downy mildew is worse during cold weather. If it’s attacking your spring-planted cabbage, it may go into “remission” once the weather warms up. I see this mildew on my cabbages and broccoli here and there, and I’ll usually just remove the affected leaves. Sometimes, I might harvest a head or two early if it looks like the disease is spreading aggressively.
Club Root
Club root is a root disease caused by an odd little organism called a protist. It’ll deform your cabbage roots, and they’ll turn into a big, lumpy blob instead of proper roots. This can lead to stunting and death of cabbage plants.
Like black rot, club root typically ends up in gardens via infected seeds or transplants. Make sure you’re buying your starts or seeds from a reputable source that certifies their product as disease-free.
The best way to keep your cabbage plants resilient against disease is to focus on plant health. Water consistently, fertilize, and make sure your plants are properly spaced for good airflow and access to nutrients.
Bolting Cabbages
Cabbage plants are biennial, like onions. This means that, when left to their own devices, they’ll grow during warm weather, overwinter, and produce flowers and seed the next spring. Sometimes, though, cabbage plants can get confused about what time of year it is and bolt (flower) too early. Then, you get some pretty flowers, some awful-tasting leaves, and no cabbage heads.
I’m convinced broccoli and cauliflower just bolt when they feel like it sometimes, but cabbage plants usually have a good reason, making it easier to prevent. Here are a few things that can cause cabbage to bolt on you:
Planting Way Too Early
Bolting in cabbage most often happens due to too much cold weather during the seedling stage. Prolonged temperatures below 45 (i.e., several days or more with no daytime warmup) sets the stage for early bolting. The plants will think they’ve experienced “winter” and assume it’s time to make seeds when the temperatures start to rise. That’s why timing your planting right is vital to get nice cabbage heads instead of flowers.
The general recommendation is to transplant seedlings two to three weeks before your last frost. At that point, those nice spring days are usually in full swing. But you can’t go strictly by the calendar, since every spring is different. Check the extended forecast and wait until daytime highs are looking consistently spring-like before you plant.
We like to start our cabbage seedlings indoors so we have more control over what weather conditions they’ll be exposed to while young. If winter decides to stick around for longer than usual one year, we can wait until the days are a little warmer to plant.
Seedling Stress
A plant’s main priority in life is producing seed to ensure the next generation. If a biennial plant like cabbage thinks its days are numbered due to environmental stress, it may try to produce seed early.
Seriously stressed cabbage seedlings might grow into mature plants that immediately go to flowering. To prevent that, make sure your seedlings are comfy and happy from the time they’re planted. Cabbage seedlings aren’t terribly picky, but there are a few problems that may trigger early bolting if not avoided or corrected.
These are the main things to focus on to keep young cabbage plants stress-free:
Don’t let your seedlings get rootbound. Cabbage seedlings that become rootbound in their seedling pots don’t always forget about it. They might either form small heads or go to bolting when they’re planted in the ground.
If you’re starting your cabbage seedlings indoors, don’t let them outgrow their pots. Pot up as needed until it’s time to put them out in the garden. We start our cabbage seedlings in small seedling cells, then pot them up into 4” pots to give the roots enough room once they have a set of true leaves.
Water consistently. Lack of water and water stress can also cause cabbage seedlings to start flowering as soon as they’re big enough to.
Provide proper nutrients. While cabbage benefits from fertilizing for the highest quality heads, nutrient issues aren’t a major cause of bolting for plants grown in the ground. It might be your problem, though, if you’re growing in containers or raised beds. Container plants don’t have access to the nutrients naturally present in native soil. Heavy feeders like cabbage will need more fertilizing to stay healthy, when grown in container soil mixes.
Excessive Heat
Sometimes, even cabbage plants that were happy and healthy as seedlings may bolt if exposed to long periods of high heat. Cabbages really don’t enjoy temperatures over 75 F, and they may decide to bow out early once daily highs are 80 F or above.
To avoid heat stress, plant your cabbages early enough they can mature before the hottest weather starts. Some cabbage varieties are bred to grow down south and can tolerate more heat than others.
If you have some hot weather earlier than normal, putting up some 40% shade cloth will help a lot to prevent your cabbages from stressing.
What Causes Loose or Poorly-Formed Cabbage Heads?
Like bolting, loose or small cabbage heads happen due to unfavorable conditions during the plants’ growth cycle. Pretty much everything in the above section can also cause poor head quality.
Lack of nutrients, particularly nitrogen, negatively affects head development. Cabbage will form the best heads when you add some nitrogen-rich fertilizer several times throughout the growing process. Underwatered cabbages tend to form poor heads, as well, especially if they experience water stress around the time the head starts to form.
A few other things that may lead to loose heads are pest attacks and heat stress. That’s one more reason to use shade cloth and insect netting for your cabbages.
Sometimes, factors outside your control might lead to a crop of less-than-perfect cabbages. We seem to always have a few that don’t form the firmest heads, some years more than others.
The good news is that loose cabbage heads are still great to eat. It doesn’t affect the flavor of the cabbage, only the storage potential. Loose cabbage heads won’t keep in the fridge for a long time like firm ones, but you can still cook them, eat them in coleslaw and salads, or preserve them.
Read this most for more about growing cabbage plants, including water and fertilizer needs: Growing Cabbage From Seed to Harvest (Spring or Fall).
