Clear the land eight weeks before planting. Then, immediately before planting, plough the ground with a disc harrow or other suitable implement to a depth of 450mm to 600mm. Cabbages can be planted by direct seeding or by transplanting seedlings. If direct seeding is chosen, about 2kg seed/ha will be required. Seedlings should be transplanted as soon as they reach the desired size, using only well-hardened, stocky, young plants.
Do the transplanting in moist soil. The soil around the roots must be firmed and irrigated as soon as possible after the seedlings are set. In wet areas, cabbages should be planted on raised beds or ridges to reduce water-logging and stem or root rot. Populations of 40 000 to 45 000 plants/ha are best for large-headed types, 55 000 to 65 000 plants/ ha for cultivars with medium-size heads, and 80 000 to 100 000 plants/ ha for baby cabbages. Plant large-headed cultivars at a row spacing of 600mm to 700mm, and 450mm in the row. Plant rows, and smaller-headed varieties, at a row spacing of 600mm and 300mm in the row.
How to Fertilise cabbages
Fertiliser programmes must be based on soil analyses for the specific land. Generally, cabbages require 200kg/ ha to 250kg/ ha nitrogen, supplied in split applications, with 50% to 66% broadcast and ploughed in, with phosphorus and potassium, just before planting. The balance is side-dressed two to three weeks after transplanting and again three weeks later, or applied once at about six weeks.
The crop needs plenty of calcium, which may be deficient in acid soil, in soil with a very high potassium content or in very dry soil. Use calcium nitrate sprays. Magnesium may be deficient in acid soil, in very light soil or in soil high in potassium. Spraying the plants with 5kg/ha magnesium should rectify the problem. As cabbages are highly susceptible to molybdenum deficiency, plants should be sprayed with 125g sodium or ammonium molybdate in 500l water/ ha as soon as signs of deficiency are noticed.
Iron may be lacking in alkaline soil. If so, apply it with a foliar spray with 1% iron sulphate or chelate. Manganese deficiencies occur in soils with a pH of more than 5,5. Use a foliar spray of 5kg/ha manganese sulphate or 2kg/ha to 3kg/ ha manganese oxide as soon as symptoms of deficiency appear. Finally, cabbages may have a boron deficiency in areas with high rainfall. This can be remedied with 3kg/ha Solubor. Weeds are controlled mechanically, manually or chemically by applying a registered herbicide. Ask your extension officer for advice.
Irrigate immediately after sowing or transplanting. Thereafter, irrigate at intervals of 10 to 12 days in heavy soil, or eight days in light soil, until the heads are fully developed and firm. Young plants must receive enough water for vegetative growth before forming heads. Excess moisture when the heads have formed may cause them to crack.
When to harvest cabbages
Harvest the crop when the heads attain their full size and become firm and hard but tender. If harvesting is delayed, the heads may split and rot, while heads harvested early may be soft.
Source: Production Guidelines for Cabbage, Department of Agriculture, Directorate Plant Production.