I have a head of cabbage that's getting so swollen I know it's going to split. Especially if a thunderburst drenches the ground. And after that head splits, my other cabbage heads, not as far along as the first, are also likely to swell, then split.
I'm not going to sit back and accept splitting cabbage heads, which happens when wet soil suddenly pumps water up into a fully ripe cabbage head. A quick yank on the neck should keep any head together. I'll straddle a swollen head, grab it with two hands, then give it a short jerk skyward. This seemingly brutal act should sever just enough small roots to stave off any rush of water.
Another approach, of course, is to just eat the head — if I'm ready. A freshly harvested head of a good variety of cabbage is a treat, even if it's not quite as tasty as one maturing during the cool, moist weather of autumn.
DECAPITATE FOR TWO CABBAGE CROPS
Actually, you could harvest a crop now and then again in autumn from the same plant. Just cut the head, when harvesting, just above the bottom whorl of leaves. You were going to discard those outer leaves anyway.
A cabbage head is really just a stem, a compressed one but otherwise like any other stem, with leaves at each node and a bud just above the point where each leaf is attached. Instead of being spaced inches apart along the stem, as with many plants, cabbage leaves grow closely one after another, each one wrapping around lower ones to form a head.
Perhaps you have made a houseplant grow more side branches by pinching off its growing tip. This pinch quells production by that top bud of a hormone that suppresses growth of buds lower down along the stem. Similarly, cut the head off a cabbage plant and buds further down along the stem are free to grow out into new stems, i.e., more heads.
Two, three, even four or more new heads could grow on your decapitated cabbage plant. However, there are limits to how much water and how many nutrients the plant can take in, and there's room for only so many new heads. More heads mean smaller heads, so you can "put in your order" for how big a head you want to harvest in autumn by adjusting the number of new heads.
OR SOW SEED FOR FALL HARVEST
A more conventional way of growing autumn cabbage is to plant seeds — now! Choose a shorter-season variety.
No matter if you don't have space in the garden now for cabbage plants. Sow seeds in flats or individual pots filled with potting soil. All they need is a few inches of space between them for the next month or so in the containers. After a month, there should be some space freed up in the garden, perhaps from an early planting of bush beans or sweet corn, or from later plantings of lettuce.
No need to plant a whole row of cabbages; you can spot individual cabbage plants here and there — even among flowers — wherever space permits.
As with the decapitation method of growing cabbages for autumn harvest, you can adjust the head size of the cabbage transplants you set out next month. Just space them closer for smaller heads.
All this talk may seem like more than is warranted for so common a vegetable as a cabbage. Plant the old variety Early Jersey Wakefield, though, and you'll see that the herbage warrants the verbiage.