Growing kohlrabi in home gardens
A quick guide to kohlrabi
- Direct seed kohlrabi in the garden from mid-April until early May, and again later in July.
- Avoid planting kohlrabi where you have grown related crops—broccoli, cauliflower, collards, kale, turnip, rutabaga, cabbage, mustard, bok choy, Brussels sprouts—during the previous four years.
- The best quality kohlrabi is sweet, crisp and juicy.
- Fast growth without heat or moisture stress results in a good crop.
- Harvest kohlrabi when the bulb is two to three inches in width. If the bulb gets too large, it will become tough, woody and bitter.
An odd-looking garden plant
Kohlrabi (Brassica oleracea var. gongylodes) is an odd-looking garden plant. It has a bulbous, enlarged stem just above the soil surface, topped with upright thick leaves.
In the kitchen, you can serve kohlrabi raw as part of a raw vegetable platter, sliced into a salad or grated into a slaw. You can also slice and use it in stir-fries or sautés. Delicious kohlrabi is crunchy, juicy, and has a mild, sweet, “cabbage” flavor. Once harvested, the leaves are also tasty. You can use the leaves as cooking greens.
The same species as cabbage, cauliflower, broccoli, turnip and kale, kohlrabi has many of the same gardening needs. It does best in cool weather, between 65°F and 75 °F, and when planted in fertile, moisture-retentive soil.
Soil pH and fertility
- Grow kohlrabi in loamy, well-drained soil with high organic matter.
- You can grow acceptable crops on heavier soil as long as it is well-drained, and on sandy soil if you water it often.
- Have your soil tested.
- A neutral soil pH of 6.0 to 7.5 is ideal.
- Apply phosphorus (P) and potassium (K) according to soil test recommendations. Many Minnesota soils have enough phosphorus.
- Unless your soil test report specifically recommends additional phosphorus, use a low- or no-phosphorus fertilizer.
- Improve your soil by adding well-rotted manure or compost in spring or fall.
- Do not use fresh manure as it may contain harmful bacteria and increase weed problems.
- If you use manure or compost, you may not need more fertilizer applications, depending on how much organic matter you use.
- Side-dress with fertilizer when the plants are about four inches tall.
- Do not use any fertilizer containing a weed killer ("Weed and Feed"), as it may kill your vegetable plants.
For a spring crop, choose a variety with a low number of days to harvest. Look for days to harvest of 35 and 45 on the seed packet. It is better to grow giant kohlrabi as a fall crop.
- Direct seed kohlrabi in the garden from mid-April until early May, at one inch spacing, and one-fourth to one-half inch deep.
- Avoid planting after May 1. The high temperatures will not produce good quality.
- Thin emerged seedlings to create four inches of space between plants.
- The cooler daytime temperatures of April and May are good for these plants, but Minnesota spring weather is unpredictable.
- If the plants experience late spring frosts, or more than a week of nights below 50°F, they may bolt (produce a flowering stalk and stop growing) once warm weather returns.
Starting seeds indoors
Some gardeners begin kohlrabi indoors to get an early start.
- Start seeds indoors in early April, or four to six weeks before transplanting.
- There is no need to use a heating mat as you might for other seeds. Cool room temperatures between 60°F and 70°F and bright overhead light will result in the best growth of the plants.
- High temperatures cause rapid growth rate, producing tall, weak plants that are difficult to handle without causing damage.
- Apply fertilizer to developing seedlings when the first true leaf appears. Use a half-strength starter solution once a week. After two true leaves are present, apply fertilizer twice a week.
- When the plants have four or five true leaves, reduce watering. Place plants outside where they will receive wind protection and a couple hours of sunlight.
- Gradually expose them to more sunlight over the next week or two, bringing them indoors if night temperatures drop below 40°F.
- Dig small holes with a trowel, or dig a narrow trench with a shovel.
- Place the seedlings four inches apart, and fill the soil around them so that the plant is at the same level it was in its pot.
- Water the plants in, or use a transplant starter solution high in phosphorus and low in nitrogen and potassium.
Plant seed directly in the garden in July. Giant kohlrabi takes about two months to mature. A late July planting will be ready to harvest before a hard freeze.
- Plant seed shallowly at one-fourth to one-half inch, three seeds every four inches.
- Keep the soil moist during seedling emergence.
- After the seedlings emerge, thin to one plant every four inches, or every 12 inches for giant types.
- Take care of the seedlings, as they experience extreme heat, wind, drought and insects when they are most vulnerable. Water them as needed.
- Space giant kohlrabi four inches apart until they are two inches in width, then harvest some of them so that there are 12 inches between plants. The plants that remain will grow to eight or ten inches in width over the next few weeks.
A row cover will protect the plants from wind and insects during the first weeks of growth. Use a lightweight material so that temperatures do not get too hot under the cover.
If strong winds loosen a floating row cover, it can do more damage than the plants would suffer without it. Anchor it firmly with soil and/or pins at the edges. You can also support the row cover with wire hoops.
How to keep your kohlrabi plants healthy and productive
- The best quality kohlrabi—sweet, crisp, juicy—results from fast growth without heat or moisture stress.
- If the plants are overheated or struggling to take up water, they will produce chemicals that have strong, bitter flavors. The bulbs will also become fibrous and may crack.
- One inch of rainfall per week is good.
- Use a trowel to see how far down the soil is wet. If it is only an inch or two, keep the water running.
- An inch of water will wet a sandy soil to a depth of ten inches, a heavy clay soil to six inches.
- If your soil is sandy, water more often than once a week.
- Frequent, shallow cultivation will kill weeds before they become a problem.
- Cultivate just deeply enough to cut the weeds off below the surface of the soil.
- Be careful not to damage the plants when cultivating.
- Mulching with herbicide-free grass clippings, weed-free straw, or other organic material to a depth of three to four inches can help prevent weed growth, reducing the need for frequent cultivation.
Flea beetles chew small holes in leaves. Seedlings are vulnerable to injury.
Cabbage maggots feed on the roots and injure the plants, sometimes killing them.
- A variety of diseases harm kohlrabi, including alternaria leaf spot, black rot, black leg, and clubroot.
- Many diseases come on infected seed. Always purchase clean, disease-free seed from a reliable source.
- Use good cultural control practices to reduce disease problems to a good level and have a successful harvest.
- Practice crop rotation. Avoid planting kohlrabi where you have grown related crops—broccoli, cauliflower, collards, kale, turnip, rutabaga, cabbage, mustard, bok choy, or Brussels sprouts—during the previous four years.
- Harvest kohlrabi when the bulb is two to three inches in width.
- If the bulb gets too large, it will become tough, woody and bitter.
- Spring-planted kohlrabi harvested in summer is more likely to become fibrous if you allow them to become over-mature.
- Fall-harvested kohlrabi can grow a bit bigger without losing quality.
- Some varieties can stand cold weather in the garden without splitting. If you plan to grow lots of kohlrabi and harvest it into the cold of autumn, choose a variety known for this “field holding” ability.
- Pick giant kohlrabi varieties when they have reached a good size.
You can store kohlrabi for months in cold, moist conditions: 36°F and 95% humidity. It is hard to create these conditions outside of commercial storage facilities.
In the home refrigerator, kohlrabi will keep its quality for about two weeks.
You can also freeze kohlrabi.
Reviewed in 2018