This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This distinct-looking vegetable (Brassica oleracea Caulo-rapa) is about halfway between a Cabbage and a Turnip. The stem is swollen into a roundish turnip-like mass or "bulb" which varies from 3 to 8 in. in diameter, the smaller size being more valued for human use, the larger ones for cattle. As a market-garden crop it is not yet extensively grown. There are two principal varieties - the white-bulbed or Green Kohl-rabi, and the Purple Kohl-rabi. According to the Returns of the Board of Agriculture and Fisheries, there were 13,330 ac. of Kohl-rabi grown in 1911. Suffolk apparently is the largest Kohl-rabi-growing county in the kingdom, with nearly 1300 ac.
Fig. 477. - Kohlrabi.
Kohl-rabi flourishes in rather a heavy soil that has been deeply dug and well manured. The seeds may be sown in drills about 18 in. apart, the young plants being afterwards thinned out to at least 12 in. apart in the rows, giving about 30,000 plants to the acre. The seeds may also be sown in beds from which the seedlings are transplanted 18 in. apart every way, a little less than 20,000 plants to the acre. From 20 to 40 tons of "bulbs" may be obtained to the acre. The bulbs are best for household purposes when young and tender, and 3 to 4 in. in diameter.
Being a Crucifer Kohl-rabi is subject to attack from the "clubroot" fungus (Plasmodiophora brassicce), and should therefore not be grown in soil known to be afflicted with this disease until it has been well dressed with basic slag, lime, or chalk. [J. W].