University of Kentucky -- College of Agriculture -- Department of Horticulture and Landscape Architecture

KOHLRABI

Brassica oleracea

CULTURE: Kohlrabi does best grown in cool temperatures but it can be grown in moderate temperatures also. Rapid growth makes a more tender plant. Stress causes the stems to become fibrous and woody. Harvest swollen stems at 2"- 3" diameter.

SOIL:

• The RAFT system uses a commercial growing medium that allows the water to be wicked up through the bottom of the pot from the mat. We used mum pots successfully to grow kohlrabi.There is no need for plowing, tilling, or soil amendments. There is no need for repeated tilling to loosen the soil to improve aeration. The soilless mix allows for good air movement even though the mix is constantly moist.
• Standard Field Practice: The plants like to be grown in a rich, well drained soil.

SEED: 6,000 - 9,000 / oz.

GERMINATION:

• The RAFT system allows the kohlrabi seed to stay constantly moist, not water logged, and not dry out during the germination process. This seemed to improve germination rates. I found that most seed germinated with earlier germination times.
• 10 days at 70F. Cover seed lightly after sowing.

DAYS TO MATURITY:

• The RAFT system allowed the plants to grow continuously and uninterrupted. Since the RAFT system provides constant water, most plants matured within the expected range of time.
• 50 - 60 days days to maturity

SPACING:

• The RAFT system allows you to seed directly into the containers or transplant. It is probably best to transplant kohlrabi so there is no need to thin for desired spacing. This results in less seed use. We used mum pots to grow kohlrabi and transplanted 5 to 8 plants per pot because these plants are smaller than other cole crops. Using individual pots of soilless mix allow plants to be spaced at any desired distance. At any time during the growing period, the pots can be re-arranged for more or less space if desired. The RAFT system is also well adapted to "square foot gardening". Plants can be placed on the raft in such a way that all of the growing surface is used. Every available square foot is occupied. The RAFT system eliminates the need for walking paths in the growing area. Each plant receives only the amount of space needed for its growth - resulting in more plants per square foot.
• Standard Field Practice: Sow seed in rows 1" apart and 1/2" deep. Thin to 6" between plants.

FERTILIZER & pH:

• The RAFT system allows a fertilizer to be placed in the water so there is a constant supply of nutrients to the plants. The fertilizer concentrations can be monitored and added when needed. Micro nutrients also can be added to the water. We maintained fertilizer levels at 80 to 100 ppm nitrogen.
• Standard Field Practice: pH 6.0+. A light application of 10-10-10 is recommended.

WATER:

• The RAFT system allows the plant to have a constant supply of water. However, the soilless mix is not soggy. To keep the water level at a uniform depth, a float valve can be attached to the float beds to fill from a storage tank or hooked directly to a water line.
• Standard Field Practice: The plants need to be irrigated regularly for continuous, tender growth.

DISEASES: clubroot, fusarium wilt, blackleg

INSECTS: flea beetles, cabbage loopers, aphids

WEEDS:

• The RAFT system has no need for chemical weed control because the growing medium is usually weed free. If weeds appear in the pots, they are easily removed by hand.
• Standard Field Practice: Chemical control, mechanical cultivation, hand pulling. In the field there is a constant battle with weeds due to an infinite supply of weed seed in the ground that is constantly germinating.

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