Brassica oleracea (gongylodes group) (Brassicaceae or cabbage family)
Production
Soil preparation
- Kohlrabi should not follow other cole crops.
- Apply compost and other amendments based on the results of a soil test.
- Spread lime as needed to increase both the pH and Ca levels. Dolomite lime will also increase Mg levels. Spread gypsum when calcium levels are low but pH is correct.
- A fertilizer company can add OMRI-listed potassium sulfate to compost if it doesn’t have enough K to meet the crop’s needs. If this isn’t possible, spread the correct amount of fertilizer and incorporate it before planting. Alternatively, you can side-dress it during cultivation. Divide the recommended rate of the soil test in half if side-dressing.
- Test for boron and apply only as recommended by the soil test. A fertilizer company can add boron to compost to optimize boron distribution. If this isn’t an option, distribute soluble boron through a water solution with a sprayer directly on the soil. If applied directly on the crop don't exceed more than 1 lb. of boron per acre to avoid leaf burn.
Common recommended fertilizer rates1
| Nitrogen | Phosphorus | Potassium | pH |
| 120 | 20-160 | 0-200 | 6.2-6.5 |
| 1Rates are for New York and are from Cornell University’s Nutrient Guidelines for Commercial Vegetable Production (2019). Check the Cornell website for updated guidelines, or consult with local experts for recommended rates outside New York. | |||
Varieties
- Indiana variety trial
- Winner, Kolibri for fresh market and Kossak for winter storage
Greenhouse guidelines
- EZ Seeder seeding plate #9
| Cell pack tray | Germination temp | Growth temp | Hardening off | Notes |
| 72, 98 or 128 | 65°–85° | Cool | Withhold water | You can seed 2 seeds per cell to increase transplanting speed. Put plug trays on a wire mesh bench to encourage air pruning. Take plants outside 1 week before planting in the field. |
Number of successions
- Spring: Kohlrabi doesn’t do well during hot and dry weather. Plant kohlrabi 4 weeks before you’re able to plant in the ground. Plant every 10 days for continuous spring to early summer harvest. In New York this is limited to 2–3 successions.
- Fall: Kohlrabi does well as a fall crop. In New York, seeding is resumed in July on a weekly basis until 4–5 weeks before the first frost. This allows continuous harvest until late November.
Signs to watch for and what to do
- Kohlrabi plants tend to get leggy. Provide enough light.
- Harden plants off outside; plants that are lush don’t perform well in the field.
Transplant readiness indicators
- Plants should easily come out of their cells. Plants should generally not be older than 5 weeks.
Transplanting in 5- or 6- foot raised beds
| Rows | In-row spacing | Planting depth (inches) | Notes |
| 3 | See notes | Normal depth, level with the top of the root ball | Given the close spacing, a carousel planter works well. For single plants, use an in-row spacing of 5 inches. For double plants, use 10 inches. |
Cultivation procedures
- Use a basket weeder or wheel hoe when weeds are in the white thread stage, without burying the young crop. Weed control is more effective when you eliminate weeds before they emerge.
- Hand hoe between plants.
- When new weeds emerge use side knives or sweeps only. Hand weed as needed.
Disease and insect protection
- Flea beetles
- Cover the crop with floating row covers or insect netting after transplanting to avoid flea beetle damage. Keep covered until harvest. Alternatively, use a spinosyn-based product like Entrust.
- If possible, follow Extension bulletins that publish the timing of each generation of flea beetles, or place yellow sticky cards at plant height to monitor their presence. Check the cards at least twice a week.
- Spray beneficial nematodes on heavily infected land to control flea beetle grubs and avoid future generations. Flea beetles tend to overwinter in nearby hedgerows and grass strips.
- You can prevent cutworms by spraying the soil with the beneficial nematode Steinernema carpocapsae. Once the pest is in the crop, control the population by spraying the crop with Bacillus thuringiensis kurstaki, or spread a baited product containing spinosyn, like Seduce, around the plants.
- Cabbage maggots: To reduce infestation of cabbage maggots on young seedlings, cover seedlings with floating row covers or insect netting as you would for flea beetles. Maggots appear in 3–4 generations in the Northeast, starting in early spring.
- While kohlrabi is considered a short-season crop, and damage might be minimal, the presence of worms makes a crop unmarketable. Therefore, scout for the eggs of imported cabbage worms or diamondback moths on the underside of leaves. When the small worm population is over 2 per plant, spray a Bacillus thuringiensis (Bt aizawai or Bt kurstaki) product, such as XenTari, or a spinosyn-based product, such as Entrust, every week until the population is under control. Alternate your spraying schedule by using Bt products along with a spinosyn-based product to avoid resistance buildup.
Other cultural practices
- Irrigate frequently for optimum yield and plant health. Frequency depends on soil type, evaporation, precipitation and the particular needs of the crop.
Cover cropping and/or double cropping
- Early kohlrabi can be followed by a transplanted short-season vegetable crop like spinach or lettuce. Mow plants as low as possible with a flail mower. Incorporate crop residue.
- For later dates, work under any harvest remains to avoid insect or pathogen buildup, and plant a cover crop. In the northern United States and Canada, you can follow summer- and early-fall-harvested kohlrabi with a cover crop of oats and peas in September, or rye and vetch planted at later dates. Adjust accordingly in other regions.
This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through the Sustainable Agriculture Research and Education (SARE) program. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.