Kohlrabi

The edible part is the rounded, swollen stem that sits just above the ground, with a few stems and leaves growing from it. It is not a root vegetable, and its flavor is similar to turnips but milder and sweeter.

It is a biennial, and if it is left in the ground for a second year it will bloom and set seed. The plant stays low, usually 6 inches to 1 foot (15 to 30 cm) tall.

When and how to sow. Sow seed directly in the garden 1 to 2 weeks before the last spring frost, about ¼ to ½ inch (0.6 to 1.3 cm) deep. Another guide says to sow in early spring as soon as the soil can be worked. For a fall crop, sow in mid-summer; in central Iowa that means mid-July to mid-August. For an earlier harvest, seed can be started indoors 4 to 6 weeks before transplanting outdoors. Seedlings can also be bought and planted in spring or fall.

Site and spacing. Choose a sunny spot with fertile, moist, well-drained soil rich in organic matter. Thin seedlings once they have their first or second set of true leaves. Sources differ on the final spacing: about 6 inches (15 cm) apart in the row, with rows 1 foot (30 cm) apart, while another guide gives 2 to 5 inches (5 to 13 cm).

Watering. Water often because the roots are shallow, aiming for about 1 to 2 inches (2.5 to 5 cm) per week. Uneven moisture can make the stems tough and woody.

Mulch and weeds. A 2 to 3 inch (5 to 8 cm) layer of mulch such as straw or grass clippings helps control weeds and conserves soil moisture. Cultivate carefully so you don’t damage the shallow roots.

Feeding. Get a soil test before planting and feed according to the results, and make sure the plants get enough nitrogen.

Possible diseases include downy mildew and bacterial rot. Common pests include aphids, cabbage loopers, cutworms, flea beetles and cabbageworms. Flea beetles chew small round holes in the leaves, and cabbageworms can be treated with products containing Bacillus thuringiensis (Bt).

Kohlrabi generally has few insect or disease problems in the home garden. Temperatures below 45 °F (7 °C) will cause the plant to flower, and hot weather makes the stem woody and tough.

Harvest when the swollen stem is 2 to 3 inches (5 to 8 cm) across. Larger stems tend to be tough, woody and bitter. The mildest flavor comes from small bulbs, and you can start picking at about 1 inch (2.5 cm) across. Pull the whole plant or cut it off at ground level.

Store it in perforated plastic bags in the refrigerator for up to 3 weeks. Another guide says to remove the leaf stems and store the unwashed bulbs in sealed plastic bags in the refrigerator.