Spring and fall are the best times to grow sweet, cabbagy kohlrabi, which thrives and tastes better in cool weather. Like so many brassicas, this odd looking vegetable is of the species Brassica oleracea with the group name "Gongylodes", a name that translates to "round" or "swollen" in Latin. This refers to its round, edible, bulbous stem that looks much like an above-ground turnip. In fact, another common name for this veggie is "turnip cabbage."
There are quite a few appealing kohlrabi varieties available to gardeners. The giant green 'Kossak' is my favorite because its bulbs stay crisp and are slow to get fibrous and woody (a problem with many kohlrabi variants). Some also stand by the massive, green 'Gigante', but in my experience the bulbs get fibrous fast. The smaller, flavorful varieties 'Winner' and 'Grand Duke' are also super sweet and stay crisp, but both are plain green. That's where the vivid purple 'Kolibri' reigns supreme. No kohlrabi is prettier at market, and the crisp fiberless flesh has a wonderful balanced sweetness. It grows quickly, too. (To learn more about kohlrabi varieties, check out Cornell's Kohlrabi Trials.)
Here are the basics for knowing and growing this fine cool-season veggie:
Common Name: Kolibri Kohlrabi
Botanical Name: Brassica oleracea (Gongylodes Group) ‘Kohlibri'
Days to Harvest: 45
Light: Full sun
Soil: Rich, friable loam
Common Problems: Cabbage loopers, damping off caused by Pythium and Phytophthora fungi, heat (causes woodiness and bolting), slugs, snails.
Planting Time: Late February for spring crops and late August for fall crops. Southerners can plant in October for winter crops.
Days to Harvest Timeline
Starting Seeds: Start plantlets indoors for best results. Sow seeds in cells filled with seedling mix and lightly sprinkle a bit on top to cover. Gently moisten the cells with water and place right under the warmth of grow lights. In 5 to 10 days your kohlrabi seeds should germinate. Germination is best in cool temperatures (50° and 60° Fahrenheit (10-15° Celcius)). (For more details visit my Black Gold seed starting post.)
Tending Seedlings: Kohlibri kohlrabi seedlings have purplish seed leaves with two lobes. True leaves start to appear in 2 to 3 days. Continue to keep plants lightly moist and lightly feed with diluted all-purpose fertilizer once the seed leaves have appeared. To avoid leaf burn, lift grow lights up as seed leaves get closer to the bulbs. (*Grower's warning: wet soil can encourage fungal disease and cause seedlings to rot or "damp off.")
Moving Small Plants: Small plants have purplish leaves and stems and should be around 3 to 5 inches tall and garden ready after 14 days. Before planting, amend and turn the soil with rich compost and organic granular fertilizer formulated for vegetables. Plant between 8 and 12 inches apart. Keep plants moist, not wet. After another 8 to 10 days they should begin to bulb up at the base. (*Grower's warning: this is the time when plants are most vulnerable to pests. Protect from cabbage loopers with BT (Bacillus thuringiensis), which is approved for organic gardening.)
Harvesting Mature Plants: In 45 days the tender bright purple 'Kolibri' bulbs should be ready to cut from the base and harvest. Ready bulbs should be between 2.5 to 4 inches across. With a harvest knife, neatly cut plants at the root, take off top leaves, bag and store in the
refrigerator. These 2.5 to 3 inch bulbs are very tender and just ready to harvest.
Preparing Kohlrabi: All bulbs should be lightly peeled before cooking or eating unless their skins are exceedingly tender. My German husband likes to chop kohlrabi into cubes and cream it with a spicy nutmeg cream sauce (roux, whole milk or cream, nutmeg, salt, pepper and hot sauce). This is delicious.
The bulbs can also be eaten raw. My good gardening friend, Ann Mattingly, grew up eating kohlrabi bulbs like apples and advocates chopping the bulbs into raw sticks and dipping them into hummus. Another tasty raw option is to julienne the bulbs on a mandolin and add them to salads as you would shredded cabbage.