Q: My cabbages are not forming heads this summer. What am I doing wrong?
A: We got this question from a couple different people this week. One gardener was growing red cabbage and the other was growing Napa cabbage. Both types of cabbage were failing to form heads, although they’d been in the ground plenty of time and the gardeners had had success in the past. So what’s up?
Several things can cause cabbage to fail to form heads. Some are in your control and some aren’t.
Hot weather can cause cabbages to fail to form heads, or to form heads that are small or strangely shaped. There’s not a lot you can do about that, but keeping them well-watered can help. Cabbages should be watered with a good, long drink, but not too often. Frequent shallow watering is less effective.
Cabbages may also fail to form heads if they are too crowded. When you plant, check the seed packet for its instructions about spacing. When I transplant little cabbage seedlings into the garden, I often put them closer than I should because it’s so hard to picture how huge the plants are going to get.
But crowded cabbages can make smaller heads or no heads. Depending on your variety, cabbages should be planted at least 18 inches apart.
There is also a possibility that something more serious is going on. A disease called clubroot can cause cabbages to fail to form heads. Clubroot can also cause plants to wilt and leaves to yellow.
You can tell whether you have clubroot by pulling up your plant and examining the roots. The roots will be swollen and distorted, possibly forming a “club” sort of like the club you’d imagine a cartoon caveman using. There are photos of clubroot at
extension.umn.edu/plant-diseases/clubroot.
Clubroot can enter your garden on infected transplants or in infected soil or compost. It can affect all kinds of plants in the brassica family, such as broccoli, collard greens, cauliflower, radishes, turnips, kohlrabi, mustard, arugula and Brussels sprouts.
If you do have club root, you should not grow brassica in that soil for seven years. Do not compost the infected plants in your home compost unless you’re certain that your pile gets to at least 148 degrees.
Here’s hoping that your plants just got too crowded this year, as clubroot can really limit what you plant in future years.
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