Kohlrabi, a member of the Brassica family that also includes cabbage and broccoli, is a unique vegetable known for its swollen, globe-like stem that develops above ground. This plant, whose name translates from German as “cabbage turnip,” has a mild, sweet flavor and a crisp, juicy texture. It is a cool-season crop, easily grown in home gardens, and comes in both pale green and purple varieties. Achieving a successful harvest requires attention to timing, consistent care, and, most importantly, proper spacing to allow the edible bulb to develop fully.
Getting Started: Timing Your Planting
Kohlrabi thrives in cooler temperatures (ideally between 65°F and 75°F) and cannot tolerate the stress of extreme heat. For a spring harvest, start seeds indoors four to six weeks before the last expected frost date. Transplant these seedlings outdoors approximately one to two weeks before the last frost, as the mature plants can withstand a light freeze.
For a fall crop, which often yields a sweeter flavor due to the cooler maturation period, direct-sow seeds in the garden about 90 days before the first anticipated fall frost. To ensure a continuous supply of tender bulbs, practice succession planting, sowing small batches of seeds every two to three weeks until mid-June for spring plantings, or until the suggested late-summer cutoff for fall plantings. Starting seeds indoors offers an earlier harvest, but direct seeding is also a viable option once the soil is workable.
Optimal Spacing for Successful Growth
The distance between kohlrabi plants is the most significant factor in determining the final size and quality of the edible bulb. Plants should be spaced at least six to eight inches apart within the row to encourage the development of a tender, marketable bulb. Some recommendations extend this spacing to eight to twelve inches for varieties that naturally grow larger.
The space required between parallel rows is typically twelve to eighteen inches, which is necessary for good air circulation and easy access for weeding and harvesting. When direct-seeding, sow seeds densely and then thin the seedlings once they have emerged and are established. Thinning removes excess seedlings to ensure the remaining plants have adequate resources and room to grow. Overcrowding prevents the stem from swelling properly, often resulting in small, woody, and less palatable bulbs.
Essential Environmental Needs
Kohlrabi requires a location that receives full sun, meaning a minimum of six hours of direct sunlight daily, to power its rapid growth cycle. The soil should be rich, fertile, and well-draining, with a high concentration of organic matter to support the plant’s shallow root system. Incorporating compost or well-rotted manure before planting is beneficial for both fertility and soil structure. An ideal soil pH range for kohlrabi is between 6.0 and 7.5.
The most common mistake that leads to poor bulb quality is inconsistent watering, which stresses the plant and can cause the bulb to split, become woody, or develop a bitter taste. Plants require about one to 1.5 inches of water per week, delivered consistently to maintain even soil moisture. Applying a two-to-three-inch layer of organic mulch (such as straw or shredded leaves) helps to conserve this moisture, regulate the soil temperature, and suppress competing weeds.
Harvesting Your Kohlrabi
Kohlrabi is typically ready for harvest approximately 45 to 60 days after planting, depending on the specific variety. The indicator for readiness is the size of the swollen stem, which should be harvested when it reaches a diameter of two to three inches. Allowing the bulbs to grow much larger than four inches in diameter significantly increases the risk of them becoming tough, fibrous, and woody.
To harvest, cut the plant cleanly at the base of the stem just above the soil line using a sharp knife. The leaves, which are also edible, should be trimmed from the bulb before storage. The harvested bulb can be stored in the refrigerator for several weeks, especially when placed in a sealed plastic bag to maintain humidity.