The trick with growing cabbage is the right timing for the formation of a good head; go too fast (or slow) and you’ll have either a bitter or loose plant on your hands. Instead of thinking of it merely as a vegetable, think of it more like a timing puzzle: It’s on a tight temperature clock. Cabbage behaves much different from most vegetables we grow in the garden (which is why most of us tend to treat it as if it were a tomato).
The amount of time it takes for cabbage to mature depends on the variety, such as green, red, or savoy. And some cabbage even take three months of cool field time before maturing (these would be your late storage kinds), whereas napa cabbage mature in about eight weeks. That’s important, because a late variety planted early in spring will often fail. A late crop relies on crisp fall weather to firm up those heads, while an early green wants to get going long before the heat of summer hits.
How to Grow Cabbage Successfully
The timeline graphic show what happens when the timing isn’t just right. To get a tight head, which is part of the goal, you have to manage your temperature: During heading time, keep the air between sixty and seventy degrees Fahrenheit. To raise your seeds in a nursery as I do, make it warmer than that; then when they begin to form heads (which is when you really want them outside), cool down those days. Above eighty degrees and the plant will cease to pack on its leaves and start moving toward bolting.
Folks tend to chalk up their problems with bolting and poor heading as due to “soil” (not good enough!) or “fertilizer” (too little!), but more likely it’s heat stress. That’s why the temperature shows up on the chart as temperature gates: Germination wants warmish soil. Sixty-five to seventy-five degrees, and the vegetative stage like cooler air.
Transplant timing matter. You don’t want the weather to turn too soon before roots is established, but you also don’t want the leaves to be too cold when they should of growing. With fall crops, it’s a race against the frost. With spring crops, it’s a race against the sun. Start seeds inside four to six weeks before the final frost date in your area. Then, transplant them after a week or so of hardening off if you are starting from seed. You want things up and growing by about the time summer really starts to cook in July.
With fall crops, you work backward, count back from your earliest hard frost date, again leaving space for the days-to-maturity plus two weeks of wiggle room. The result: heads that tend to be tighter-packed and even sweeter. Why? As nights get cooler, the plants work to turn starches into sugars as their own form of defense against a freeze. That helps with flavor, and those final couple of weeks of chillier nights make all the difference between a tasty cabbage for crunching up in slaw vs. A dull, meh head of nothing-special.
The best indicators are practical ones instead of calendar ones. You’ll know when to apply the side-dressing of nitrogen because the foliage starts folding upward; the first signs are called “cupped” leaves, the ones whose edges start curling back toward the crown of the plant. Feed too soon, and all you’ve got is a lot of lovely foliage but no core, and feed too late and now you have rotten softness in the middle.
The best way to judge doneness is the squeeze test. Squeeze: Thumb the center of each head; if it is still soft, wait a few more cool days before harvesting. If it holds up to thumb pressure, time to harvest. Another complaint: splitting heads. This usually happens because of a heavy rain after a long drought, but you can prevent it by picking the heads at the right time.
The moral of the cabbage story: Growing this vegetable is all about patience. It won’t tolerate sudden weather changes. It will only reward patience with a large crop if you pay attention to detail. You don’t have to believe me; just try it yourself sometime. Whether you are planning for a fast crop of napa or for those later greens meant for long winter storage, the process is similar. Keep the air cool and keep the roots moist throughout heading time. Watch for the sign that things are really happening: the cupping action. Cut your perfect, tight head right at ground level, and you will know what I mean; that’s why it matters so much. All that work pays off in a succesful harvest.