Becoming a good vegetable gardener often means opening your mind and your garden to unfamiliar food crops. Such is the case with kohlrabi, a vegetable virtually unknown outside Northern Europe and Kashmir until the last few decades. A thoroughly modern vegetable, historians think that kohlrabi was developed in Northern Europe only 500 years ago, mostly likely by selecting from "marrow cabbage," a type of cabbage with a thick heart. Dark brown to black kohlrabi seeds are indistinguishable from those of closely related broccoli, cabbage and Brussels sprouts. While all of these vegetables can make great garden crops, growing kohlrabi is a wise choice because it’s so fast, easy and dependable. For beginning gardeners, kohlrabi is the first cabbage family crop you should try.
Kohlrabi is, in my opinion, one of the finest delicacies in the garden, worthy of planting two or three times each season. In the garden, kohlrabi sports a trim, upright growing habit that accommodates the presence of nearby plants – something the bigger brassicas cannot do. Growing kohlrabi and beetroot together works well because the two crops grow on a similar schedule and have similar moisture needs. You also can grow kohlrabi between rows of onions, lettuce, or radicchio, where its odd appearance becomes strikingly handsome.
How Does Kohlrabi Taste?
Kohlrabi delivers the flavour of tender broccoli stems, but with a crisp texture that has earned it the nickname of "vegetable apple." Some people say purple varieties taste sweeter, but bringing out kohlrabi’s best flavour is largely a matter of good soil fertility, consistent moisture, and warm days and cool nights. In either purple or green, garden-fresh kohlrabi has the same unique tenderness found in home grown broccoli.
You can get to know kohlrabi in the kitchen by trying three simple concepts: slaw made by combining grated or julienned kohlrabi with apples, oven-roasted kohlrabi, and creamy kohlrabi soup (curry recommended but optional). Unless the bulbs are very young and tender, it’s best to peel them to avoid chewy strings. Kohlrabi leaves are eaten in some cuisines, but in my experience they tend toward bitterness and lack the tender bite of more table-worthy greens. The world record for kohlrabi stands at 97 pounds (44 kg), grown by Alaskan Scott Robb, but I’ve never eaten a really good kohlrabi bigger than a baseball.
Kohlrabi Seeds or Seedlings?
You can direct-seed kohlrabi seeds in a well-prepared seedbed, or start seedlings in small containers indoors and transplant them to your garden when they are 3 to 4 weeks old. Kohlrabi tolerates cool conditions, so you can push your planting dates up by two to three weeks by using cloches, tunnels or other season-stretching devices. I often use milk carton cloches to protect kohlrabi seedlings from harsh spring winds. Just as my last frost passes, I direct-seed a small second planting for harvest in midsummer.
When growing kohlrabi in spring, I suggest using a fast-maturing hybrid that can be harvested when the bulbs are about 3 inches (8 cm) in diameter. Typical varieties are rated at around 60 days to maturity, but often take longer. If you live in a cool climate, or any climate that permits growing broccoli and collards in the fall, that is the time to experiment with heavyweight heirloom varieties like Gigante, also known as Superschmelz, which can still be of excellent quality at 5 to 6 inches (12-15 cm) in diameter when matured in cool fall soil.
Keeping Kohlrabi Happy
Occasional cabbageworms (the caterpillars of cabbage white butterflies) may need plucking from your kohlrabi plants, though they much prefer cabbage and broccoli. Drying out is a more serious problem when growing kohlrabi, because the plants sit atop the ground and do a terrible job of shading surrounding soil. A rich mulch of freshly cut grass clippings or chunky compost is therefore necessary to keep kohlrabi’s root zone cool and moist and provide a trickle of ready-to-use nutrients for this delicious, fast-growing crop.
By Barbara Pleasant