There are three varieties of cabbages in the country namely smooth-leafed green, smooth-leafed red, and crinkled-leafed green, also known as savoy cabbage.
Cabbage grows well in full sun, but being a cool-weather crop, it can tolerate some shade during the day. It especially likes cool nights with morning dew. In highland areas, cabbage can be grown all-year round by successive sowing after every two months.
You can also plan your planting cycle in a way that uses the cooler months for growing. Also, avoid planting that will see the crop mature in hot, dry January weather.
You can sow cabbage directly in situ or grow seedlings in a separate seedbed and then transplant.
Cabbage seeds take four to 10 days to germinate and if grown in a seedbed, they should be transplanted after five to seven weeks. They, thereafter, take 80 days to mature and harvest.
So, for a July or August harvest, you should plant your seedlings in March or April. But you can also plant them on any four-month cycle as long as you avoid sowing in October or November if you are in a hotter area.
The recommended spacing is 50 by 50cm to 70 by 70cm for larger varieties. In a square-foot planting system, plant a single cabbage per square foot.
The crop is what we call a “heavy feeder”. Cabbage needs adequate nutrition to grow those heavy heads.
Therefore, it is preferably grown in soils with some clay content, but the soil also needs to be deep and rich in organic matter with a high water retention capacity. This is the ability of the soil to hold rain or irrigation water for longer periods.
To achieve this, loosen the soil deeply before planting and dig in 12 to 20 tonnes of high quality compost per acre six weeks before planting.
Cabbage also needs well-aerated soil, so loosen the soil regularly and apply mulch. A thick mulch layer of 15 to 20cm deep will help to keep the soil moist and cool. Shortly before head formation, heap up the soil around the root or stem area. This will increase root and plant growth.
I strongly recommend that you have your soil tested before you plant. A soil test will give you all the necessary information you need for successful and sustainable fertility management.
Cabbage needs a pH of 6 to 7. In case the pH of your field is lower, the recommendation that comes with the soil test will advise you on the amount of lime you need to incorporate prior to planting. Lime should be applied three to six months before planting. So do your soil tests early and regularly.
The soil test will also give you a recommendation on the kind and amount of fertiliser you should apply.
Generally, cabbage needs the following nutrient requirements: 93kg nitrogen, 20kg phosphorus and 20kg potassium. If you do not know what the fertility status of your soil actually is, feeding these amounts of fertiliser might create or worsen nutrient imbalances in your soil.
That is why soil testing is key to successful fertiliser application and, thus, farming.
It is worth noting that adequate compost manure application will offer 36kg of nitrogen, plus the nutrients from phosphorus and potassium.
Fertiliser applications should be split into two; at planting and top dressing or even into three after every six weeks. Application of homemade liquid fertiliser made from comfrey leaves at transplanting and when the heads begin to form will give the crop an extra boost.
Cabbage has high water needs, which peak after they start forming heads. Therefore, the crop is best grown under irrigation to ensure steady water supply.
If the soil dries out and then a high amount of water is given suddenly, the heads tend to crack.
Harvest during cool morning hours to avoid cracking of the heads.
Check for caterpillars and aphids regularly and dust your cabbages with wood ash from the start to avoid the pests.
Cold season planting minimises caterpillar infestation. Also, keep the soil moist or mulched to avoid flee beetle damage. Aphid infestation is a sign of heat or water stress and inadequate nutrient supply.
Typical cabbage diseases are black leg, black rot or leaf blight, club root, damping off and stem rot. If your cabbages have had problems in the past, look for disease-resistant cultivars.
To avoid soil-borne diseases, don’t plant cabbage-family plants (Brussels sprouts, kale, cauliflower and broccoli) in the same area more than once every three years. Plant cabbage after beans and follow with maize and or potatoes.
Lastly, for better growth, don’t plant cabbage near capsicum, chilli, eggplant, garlic, lettuce, maize, mustard, radish or strawberries.