- Germination Days: 7-14
- Hardiness Zone:3-9
- Planting Depth:1/2"
- Plant Spacing:4"
- Row Spacing:2'
- Growth Habit:Upright
- Soil Preference:Moist, well-drained, 6.5 – 7.0 pH
- Temp Preference:Warmer
- Light Preference:Full Sun
- Days to Maturity:60 days
The Italians first cultivated kohlrabi in the 1500s. Sometime during the 1600s-1700s the vegetable made it to the US. Purple Vienna is the earliest and sweetest of the varieties. The unearthly looking plants are 10-12 in. tall with reddish purple, bulbous roots that grow on top of the soil. Roots are best-harvested young (2 in. diameter).
Because of its turnip-like appearance, kohlrabi is sometimes misclassified as a root vegetable. Leaves stand out like little spokes on the sides and top of the edible, enlarged stem. You'll welcome not only kohlrabi's unusual shape, but also its crisp texture and wonderful, delicately sweet, nutty, and very slightly peppery.
Kohlrabi (Brassica Oleracea Gongylodes Group), also called German turnip, is a biennial vegetable, a low, stout cultivar of wild cabbage. It is another cultivar of the same species as cabbage, broccoli, cauliflower, kale, Brussels sprouts and collard greens. It can be eaten raw or cooked. Edible preparations are made with both the stem and the leaves. Despite its common names, it is not the same species as turnip.
Start seeds indoors about 4–5 weeks prior to the last spring frost. Seeds germinate quickly at temperatures between 75 to 80°F. Do not plant transplant into the garden until after the last threat of frost. Transplant outside when the ground can be worked and seedlings are 3" tall. Space seedlings 6" apart and water thoroughly after transplanting.
Cold, Cool. Kohlrabi needs full sun, and should not be planted where another Brassica has grown in at least in the previous two years, as it can lead to disease and pest problems. Kohlrabi generally does better as a fall crop, sown 6 to 8 weeks before the first autumn frost date. Autumn Kohlrabi bulbs can be allowed to get larger than 2" to 3", because cold weather seems to keep them tender (it also increases their sweetness). For spring planting, sow the first crop 4-6 weeks before the last frost date. You can make several succession sowings (very early sowings may be vernalized and bolt). In cool climates, you can continue to succession sow all summer.
Kohlrabi must grow fast for the best quality, so give the plants all the water and nutrients they need.
Water: Moderate. Keep the soil evenly moist or the bulbous stems may turn woody. This should not be an issue with this cool weather crop. Watering also depends on your local weather; don't water if it's raining, or water more frequently if it's dry. Just be sure to keep soil moist for the best crop. The best way to know how much moisture is in your soil is to feel 2" below the soil line. If it's dry, water.
Soil: Prefers well-aerated soil with a pH 6.0 - 7.0, ideal 6.4 - 6.6. Kohlrabi likes a light, rich, moisture-retentive soil, with lots of organic matter.
Containers: Yes. While kohlrabi isn't particularly well suited for container growing, it can be done in a large container. Ideally, one that is 8-12 inches deep and 12-18 inches wide. If planting multiple plants in one container, make sure they are spaced 18-24 inches apart.
Feeder: Light. Low nitrogen. High potassium. High phosphorous. It's a light feeding crop and doesn't need a lot of nitrogen, but it does like calcium.
Mulching: Mulch plant base using shredded bark, grass clippings, or bark chips to prevent water loss from soil and to keep the temperature even.
Weeding, regularly: regularly, every 3 weeks. It is best to control weeds by hand weeding, as hoeing can easily damage the shallow roots and swollen stems. A mulch will also help.
Ripening: The edible portion of kohlrabi is not the root, but rather the round, swollen stem of the plant. Leaves are also edible. Harvest when stem swells to 3-5" and is easily visible above the soil. Cut the stem an inch below the bulb, or simply uproot the entire plant if they aren’t growing too close together.