I grew kohlrabi for the first time many years ago as an experiment. I had never tasted it or even seen it sold at the grocery store, but the seed-catalog description of crisp white flesh and mild, sweet flavor inspired me to plant some seeds of 'Early White Vienna'.
About a month later, mini-satellites--bulbous aboveground growths with long-stemmed leaves shooting out in all directions--began to appear in my garden. I had never seen such an odd-looking vegetable, but the taste and texture more than lived up to their promise and kohlrabi has been a staple in my garden now for 20 years.
Despite my suspicions that it had originated on Mars, or had once orbited the Earth, kohlrabi was cultivated in northern Europe at least by 1500. The name comes from the German words for cabbage (kohl) and turnip (rabi). The leaves are distinctly cabbage-like, and the dense globe does resemble a turnip root. The flavor is sweet, milder than turnips and with a hint of cabbage. The firm, crisp texture is similar to that of a raw potato.
"Not enough gardeners know about kohlrabi," says Tom Johns of Territorial Seed Company in Lorane, Oregon. "I just peel them, slice them up and munch them right down--for fresh, raw garden fare, you really can't beat it. Even my kids love it." Both the leaves and the globes are good lightly steamed or in soups or stir-fries. Kohlrabi is also a pleasantly crunchy addition to salads and the hors d'oeuvre tray. It's an excellent source of vitamins A and C, as well as calcium and iron.
Grow this cool-season biennial in spring and fall. Timing is especially key with spring plantings. "Get the crop matured up before real hot weather," advises Tom Johns. A steady supply of water, which promotes rapid growth, is also crucial to producing a sweet, tender crop.
I start my kohlrabi in the cold frame in March here in southern Maryland. The seed, like broccoli, germinates quickly and reaches transplant size in a couple of weeks. When the plantse about three inches tall, I move them to the garden, making sure they get full sun and a light soil that's been enriched with compost and well-rotted manure. I space them about four inches apart in a staggered double row to make the most of my garden space. The tough little seedlings grow very quickly despite cool spring temperatures and don't mind a light frost.
At the same time I transplant the seedlings from my cold frame, I sow a second crop of seed directly in the garden. Unless we experience unusually warm spring weather, there is plenty of time for it to mature before temperatures climb into the 80s and its quality suffers from the heat.
For a fall crop, sow seed directly into the garden from mid-July to early August. Because of the summer heat, this late planting may need a bit more attention than the spring crop, particularly with watering. Seedlings will also need thinning to achieve proper spacing, but once up and going, they are just as carefree as the early planting. As a matter of fact, I think the flavor of my fall kohlrabi is even better than the spring crop--as night temperatures drop, the bulbs seem to sweeten up. In the Territorial Seed Company test gardens in Oregon, fall plantings of this hardy crop have held in the ground until Christmas.
Spring-planted bulbs are ready for harvest as soon as they are two to three inches across (much larger, and they'll be woody, pithy or unpleasantly pungent). You can allow the fall-planted crop to get bigger; it's maturing in cooler weather and doesn't have as much of a tendency to get woody. Cut the plant at its base and trim off the stems. After harvest, the bulbs hold up well in the refrigerator or a cool cellar for a couple of weeks.
I've never experienced any disease problems with my kohlrabi, but as a member of the cabbage family, it can be subject to the same diseases as other cole crops, such as black rot and clubroot. Bec the edible portion forms aboveground, however, it isn't damaged by cabbage root maggots. In my garden, cabbageworms appear less interested in this bulbous crop than they are in its cousins, broccoli and cabbage, but if I need to spray my broccoli with Bt, I usually apply some to the kohlrabi at the same time, just to be safe.
My favorite is 'Rapid' (60 days), which produces a bright reddish purple globe that's lovely in the garden and is especially mild-flavored, with a very crunchy texture. I also grow 'Waldema'r (60 days), a thin-skinned, white-fleshed Austrian hybrid that holds well in the garden without becoming pithy.
Here are some others for both spring and fall crops.
'Early Purple Vienna' (55 days): This purple form of the bedding plant standard described below is slightly larger and flatter, and somewhat more resistant to cabbageworms.
'Early White Vienna' (50 days): The variety most commonly offered in seed catalogs. Very uniform plants, greenish white skin and white flesh.
'Kolibri' (58 days): A heat-tolerant European hybrid with deep purple skin and crisp clear white flesh. Delicate, sweet flavor.
'Kolpak' (50 days): A new early variety with very good resistance to getting pithy or fibrous. Quickly forms light green bulbs that stay tender.
'Winner' (53 days): Produces large, uniform bulbs with light green skin and a pure white flesh.
'Grand Duke' (45 days): Uniformly shaped globes that are resistant to black rot.
This type of kohlrabi forms a huge globe that can weigh 25 pounds or more! Seeded in early spring, these varieties hold their quality in the ground for a long time and can even be overwintered in the garden in mild climates. When the temperature drops below 15° F to 20° F, protect them with buckets, straw bales or floating row cover over hoops, with a blanket or plastic tossed on top on colder nights. They also store well in the root cellar.
'Gigant Winter' (62 days from transplant to first harvest) averages eight to 10 inches and 15 to 20 pounds. Southern Exposure Seed Exchange, which introduced this Czechoslovakian heirloom five years ago, describes it as a breakthrough in kohlrabi quality. The principle advantage over smaller kohlrabis," says Jeff McCormack of SESE, "is that you can harvest 'Gigant Winter' through the season from the time it reaches several inches in diameter on up to when it's quite large and it doesn't get woody." Nichols Garden Nursery carries a similar strain, 'Gigante'.
'Superschmeltz' (60 days) is another open-pollinated strain from Territorial. "It's the only giant variety that gets uniformly large and round," notes Tom Johns. "It has a tremendous root system, so is a good choice for dry climates."
Rita Pilczar is a freelance writer and consultant based in southern Maryland.Photography by National Gardening Association