Growing Kohlrabi

Kohlrabi is an interesting vegetable that has a tender flesh with a mild flavour like that of cabbage or turnips. It is an easy vegetable to grow and a good source of vitamin C and potassium. Like other members of the brassica family, it also has cancer fighting properties.

Growth habits and planting needs

Select a site that will receive full sun to grow your kohlrabi.

The kholrabi plant has a well-developed taproot and  numerous, shallow, but widely spreading, horizontally branching roots similar to the cabbage. This extensive root system needs deeply dug friable soil that drains well and yet holds moisture. As with the cabbage and cauliflower the most dense part of the root system are in the first 20 cm.

This diagram from Root Development of Vegetable Crops by John E. Weaver and William E. Bruner shows the root development (grid in ft) for Kohlrabi of a mature plant grown under optimal conditions.

Kohlrbi root system
Source:Soil and Health Library

Dig the soil over to a depth of 40-60 cm removing clods and enrich with plenty of organic matter in the form of aged compost and aged chicken or other animal manures.

Kohlrabi do best when the pH of the soil is between 6.5 – 6.8 so test the soil and amend as required.

They need nitrogen to develop strong stems where the bulb develops like other members of the brassica family so Kohlrabi should follow nitrogen fixing legume crops in the crop rotation system, and should not follow a brassica crop.

Seeds can be sown directly into the garden bed in early Autumn and early spring.  They should be sown to a depth of 5-10 mm deep and 15 cm apart.

The kohlrabi plants will germinate in 4-10 days.

When the true leaves emerge they can be thinned to 30 cm apart and the thinned seedlings transplanted to other prepared beds.

Water with fish emulsion after the first month’s growth.

Like cabbages, kohlrabi require constantly moist soil to produce good bulbs so adequate watering and mulching is important. As the plant can have a dense spread of roots to 60 cm all around the plant stem it is important to use mulch to conserve moisture from evaporating from this extensive root system.

Mid way through the season side dress with more aged compost when the plants are around 12 cm tall.

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White kohlrabi (Image: Creative Commons CC0)

Companion Plants:

  • Beetroot, celery, herbs, onions, potatoes.
  • land cress, hyssop, rosemary, mint and sage to deter cabbage butterfly
  • garlic to improve growth and flavour.
  • nasturtium to deter aphids

Harvesting

The plant will mature in 60 -70 days from sowing and should be picked small, about golf ball size to be at its tenderest.

When the plants are mature the leaves will be about 25 cm long and the bulbous part of the stem will be about 5-7 cm in diameter.

Cut the stem 2.5 cm below the bulbs. Remove the leaves and store the bulbs in the crisper section of the refrigerator for 3 weeks.

The tender leaves can be steamed for a few minutes and then sautéed with onions for a delicious side dish to meats.

The bulbs can be eaten raw thinly sliced or thickly grated for use in coleslaw and can also be baked or cooked in a variety of ways.

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Purple and white kohlrabi growing (Image: Creative commons CC0)

 

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