Now here’s one weird looking vegetable. When I show kids a kohlrabi (Brassica oleracea), they say it looks like a satellite or spaceship. It’s always a conversation piece when people visit my garden. In spite of its looks, kohlrabi is an easy, cabbage-family vegetable to grow. It’s wildly popular in Eastern Europe, but just catching on in this country. While you can eat the leaves, it’s the round swollen stem at the base that’s mostly used. When you peel kohlrabi, it reveals a crisp, crunchy, white-fleshed vegetable that’s great shredded raw in salads or making “kohl” slaw. The flavor is like a cross between a cabbage and a turnip, but milder. You can also cook it in soups and stews.
When to Plant
Grow kohlrabi as you would cabbage. Sow seeds directly into the garden 2- to 4-weeks before your last frost date, usually April or May. You can also start plants indoors 4 weeks earlier or purchase them at the local garden center. Since they mature in only 40 to 50 days, grow some kohlrabi as a fall crop planted in late summer.
Where to Plant
Kohlrabi like full sun on well-drained soil amended with compost. This cool season crop is the least hardy of the cabbage family, so plant where they can be protected from late spring frosts.
How to Plant
Sow seeds 1-inch apart in rows 18-inches apart. Thin plants to 8-inches apart once the true leaves (second set of leaves) form. Transplant seedlings to 8 inches apart as well.
Care and Maintenance
Kohlrabi grows best during cool weather, but temperatures below 40F can cause the young plant to bolt (form a flower stalk) before forming a ball. Also, if the weather gets too hot, kohlrabi stems will be tough and woody textured. The key is to get them off to a good start and maturing before the heat of mid summer. Fall is a good time to grow them for that reason. They will mature slower, but have a more tender texture and sweeter flavor.
Once plants are growing, add a small handful of an organic fertilizer such as 5-5-5 per row. Keep the young plants weed free and well watered. Once they’re established, mulch around plants with untreated grass clippings or straw. This will help keep weeds away and keep the soil cool and moist.
Kohlrabi is attacked by similar pests as cabbages and broccoli. Rotate crops not planting cabbage-family plants in the same location for 3 years, to avoid diseases. Spray plants with Neem oil to control flea beetles or place floating row covers over plants when young. Once plants are established, flea beetles are usually not a problem. Check leaves for signs of the green cabbageworms and cabbage looper insects. Spray Bacillus thuriengensis (Bt) on plants to control this pest.
Once the swollen stem is at least 1 inch in diameter, it’s time to harvest. Pull up the entire plant and cut off the leaves and roots. You’ll get one swollen stem per plant. You can safely harvest until the stems are about 3 inches in diameter. For most varieties, any bigger than that and the stem becomes woody. You can eat them fresh or peel and dice the stems to freeze for winter use.
‘Korridor Hybrid’ produces green, sweet tasting roots in only 42 days from transplanting. ‘Kolibri Hybrid’ has a unique purple colored skin and fiberless flesh. ‘Kossack Hybrid’ is a large, green variety that’s harvested when it’s 8-inches in diameter. It can be stored in cool, dark room for several months.
Text excepted from the Northeast Vegetable and Fruit Gardening book.