Cabbage is one of the most widely-grown vegetable crops in South Africa. Excellent yields can be obtained if you know what you’re doing, and the crop can be highly profitable. Cabbage is expensive to grow though, so you need to pay a lot of attention to detail.
Soil and fertiliser: Cabbages can be produced on a wide range of soil types, but they must always be well-drained. This crop does not like “wet feet”. Soils that remain wet for long periods should be avoided. Immediately correct any acidity problems – cabbages are highly sensitive to soil acidity. Even mild acidity can drastically reduce yields.
Do soil tests so you know how much lime to apply to you soils, one to two months before planting, to give the lime time to react with the soil. Remember, cabbages demand a lot of nutrients. Here are some basic fertilisation guidelines before and at planting:
Basal fertilisation: When preparing the seedbed, large amounts of particularly phosphorus (P) and potassium (K) are usually applied by broadcasting fertiliser over the whole field, which is then disked into the top 10 to 15cm layer of soil.
While the actual rate and type of fertiliser should be based on soil test results, a typical basal fertilisation would be 1000kg/ha of 2.3.4(38)+Zn. The micronutrients boron and molybdenum are often included with this basal fertiliser.
Remember that poultry and kraal manure have valuable nutrients, improving soil heath and benefiting cabbage, so also disk any manure into the soil with your basal fertiliser.
Banded (‘starter’) fertiliser: To get seedlings to grow rapidly, a fertiliser high in P should be placed in the planting furrow or hole. The most commonly used fertiliser for this purpose is MAP+Zn, usually between 200 and 300kg/ha.
Seedlings, planting and spacing: Only use good quality seedlings from a reputable nursery that can also provide advice on what cultivars to use.
The seedlings should typically be 7 to 10cm in height and uniformly green. Remember, different cultivars are planted differently. For large-headed types, the preferred population is 35 000 to 45 000 plants per hectare, planted typically in rows spaced 60-75cm apart, and plants 45cm apart within the row.
For small to medium-sized heads, populations of 55 000 to 65 000 plants per hectare are more suitable, also with closer spacing. Be careful to always plant seedlings to the correct depth. They should be buried in the soil to the depth of the top of the plug; any deeper and they’ll die.
Seedlings must be placed vertically in the soil, not sideways. The lower end of the plug should also not be forced into a horizontal direction due to the hole or furrow being too shallow.
Horizontal bending of the lower end of the plug results in impeded root development (“J-rooting”), with consequent poor plant growth and serious yield losses. Once the seedling is placed in the soil, the soil should be firmed around it so as to ensure good contact between soil and the seedling.
Fertiliser topdressing: The nitrogen (N) applied during planting is not sufficient to see the crop through to harvest. Once the crop is established, one or two nitrogen (N) topdressings are required. Importantly, the first N topdressing must be applied before the 4-week stage of growth, and the last dressing not later than 45 days after transplanting.
The fertilisers normally used for topdressing are LAN or urea. These fertilisers tend to be equally effective, provided the crop is irrigated or receives rain within a day or two of the fertiliser being applied.
If the fertiliser is going to lie on the surface of the soil for longer than this without any moisture, then rather use LAN.
The amount of N applied in the topdressings depends on various factors, including the expected yield, the soil type and the amount of N supplied in fertilisers at establishment. The total (establishment and topdressing) amount of N required by the crop is usually in the range 200 to 250kg N/ha.
Weeds, pests and disease: Control weeds for best yields, either by hand hoeing or registered herbicides. The most important pests are cut-worm, diamond-back moth, aphids and American bollworm. Downy mildew and black rot are the main diseases to look out for.
Apply appropriate chemical sprays – ask an experienced farming specialist at your local agribusiness for advice.
Irrigation: Seedlings should be irrigated immediately after transplanting. After that, irrigation will depend on your soil type, season and the stage of growth. Sandy soils require more frequent irrigation than loams and clays.
In winter, the crop typically requires 10 to 15mm per week for the first half of its growing season, and about 25mm every week after that. In summer, the requirement may be up to double this! – Neil Miles & Neil Baxter