This vegetable is a member of the turnip family and, for that reason, is also called cabbage turnip. Like the turnip, both its purple-tinged or white bulb-like swollen stem and its greens are edible.
The kohlrabi bulb tastes like a mild, sweet turnip with a slightly nutty flavour. It’s available from mid-spring to mid-autumn. The roots that are about 3 in (76mm) in diameter are grown above the ground and are very tender.
It must be encouraged to grow quickly so that it will be tender, therefore it must be grown in fertile, moisture, retentive soil, in a position where it will get plenty of sun.
Kohl Rabi will grow on most soils providing it is well cultivated and preferably alkaline; it will tolerate a pH in the range 4.5 to 7.5. It does best in soils, which were well manured, for a previous crop.
At the time of sowing add a dressing of fish manure with 6 percent potash content at 3 oz. (90g) to the sq. yd. After forking over the soil lightly, tread the ground making it firm, and then add fish manure at 3 oz. (90g) to the sq. yd. If the soil is not limy, give carbonate of lime at 6 oz. (180g) to the sq. yd. as a top dressing.
The seeds can be sown from March to July thinly in drills, which are 1 ½ ft. (45cm) apart, at a depth of 1 in. (25mm). However, should the temperatures be low during March, then it would be better to delay sowing as the young growing plants are sensitive to low temperatures.
Even a week at a temperature in the region of 10 deg. C. will cause the plants to bolt. However, once over this initial period, the crop is very hardy indeed.
Later thin out to allow the seedlings to be 1 ft (30cm) apart by the time they reach 1 in. (25mm) high. Should you wish to have year-round harvesting, the seeds, which are to mature during the winter, can be sown under cover, then hardened off and planted in their growing bed; as they are very hardy once established they are quite capable of withstanding frost and winter conditions.
Kohlrabi grows well with onions also cucumbers and herbs. However, it does not do well if grown with runner beans, tomatoes or strawberries.
Keep down the weeds by hoeing and make sure that they are kept well watered.
Because they are quick growing reaching maturity 8 weeks after sowing, it is better to make small consecutive sowings to keep the vegetable available in the peak of condition when they are young and tender.