Kohlrabi

Similar in cultural requirements to cabbage, kohlrabi produces an edible, swollen stem. It's an odd-looking plant, good either raw or cooked. Although the plant isn't popular, most people like its turniplike taste after trying it. . 

Varieties
 Three  popular  varieties  are 'Grand Duke,' 'Early Purple Vienna,' and 'Early White Vienna.' 'Grand Duke' produces larger and milder knobs. It also resists black rot.

Planting
Because kohlrabi does best when it matures in cool weather, sow its seeds as soon as you can work the ground in the spring. Mix in lots of organic matter and some commercial fertilizer. Space rows about 2 feet apart. For an even earlier crop, start seeds indoors six to eight weeks before the frost-free date, then transplant to the garden three to four weeks before that date. Protect if necessary with cloches. Planting seedlings instead of seeds is highly recommended-but not essential--in northern gardens. Because kohlrabi matures early, it's a good candidate for interplanting with later-maturing onions. Or plant kohlrabi later in the season to mature in the cool weeks of fail.

Care
Provide kohlrabi with plenty of sun and a cool, moist soil. Add a thick mulch as soon as the plants emerge to preserve soil moisture. Water whenever the soil dries out. Avoid cultivating around the plant since it has a shallow root system. Spray weekly with Bacillus thurngiensis to prevent cabbageworm attack. If a plant wilts unexpectedly, check its roots for maggots. Kill root maggots with diazinon, or prevent them by surrounding plants with root maggot mats (5x5-inch pieces of carpet underlayment).

Harvest
Pick before the knobs grow wider than 2 inches. Kohlrabi will become tough and stringy if it ripens beyond that point. Trim leaves, which are edible but rarely eaten, and roots. Parboil the knob. Remove outer peeling before eating. Protect late plantings with mulch to extend the harvest into late fail.