Cabbage is one of the most popular vegetables in Kenya and it is important to know the various characteristics of it for both new and old farmers.

After the cabbage is planted, a rosette of sessile leaves arises as the growing point and continues to form leaf primordial. The outer leaves are green in colour and the inner ones are white. As the plant grows, the leaves increase in number, forming a ball-shaped “head” in the centre of the plant as shown below The head is basically a large vegetative terminal bud, formed by overlapping of numerous leaves developing over the growing point of its shortened stem.

Several types of cabbage are grouped into conical or sugarloaf-headed, ballheaded and drum-headed based on the shape of the head and the savoy. They can also be classified according to their colour and growth cycle. The leaves may be green or red and smooth or wrinkled. The savoy types are tolerant to cold conditions and they have deep-wrinkled dark green-leaves.

Cabbage grows best in a relatively cool and humid climate. Leaves are more distinctly petioled and the quality of the head is impaired in drier atmospheres. The delicate flavour is also lost under these conditions. Yield and quality are poor during the hot seasons  and it is also difficult to control insect pests. The optimum temperatures for growth and development are from 18 °C to 20 °C. It is fairly resistant to frost and can survive low temperatures without damage.

Cabbage is also adapted to a wide variety of climatic conditions and can such be grown throughout the year in most regions.

Water requirements vary from 380 to 500 mm per crop, depending on climate and length of growing season. Crop water use increases during the growing period with a peak towards the end of the season.

Cabbage can be grown on a wide range of soils but it thrives on well-drained, moisture-retentive loamy soils well supplied with organic matter. It does not grow well on highly acidic soil and it is important to test your soils. The ideal soil pH ranges from 5.5 to 6.5 and it should not be allowed to fall below 4.5. In soils with pH above 6.5 the leaves become dark but leaf margins die back. Plants in saline soils are also highly susceptible to blackleg.

Cultivation practices

Cabbage is propagated from seeds. To prepare for the planting,  the land should be clean cultivated eight weeks before planting and the ground must be ploughed deeply, immediately before planting, with a disk harrow or other suitable implement to a depth of 450 to 600 mm. The soil should be fumigated two weeks before planting time if necessary, to control nematodes.

Planting

Cabbage may be planted by direct-seeding or transplanting of seedlings. If direct seeding is to be used, about 2 kg of seed per hectare may be required.

Seedlings should be transplanted as soon as they reach the desired size and only well-hardened, young, stocky plants should be used. Transplanting is done on moist soil. The soil around the roots should be firmed and irrigated as soon as possible after the seedlings rare set. In wet areas, cabbage should be planted on raised beds or ridges to reduce water-logging and stem or root rot diseases.

Plant population and spacing influence head size, head shape and yield. Cabbage plant populations vary according to the target market for a particular crop. It has been reported that cabbage forms smaller and slightly more pointed heads when they are spaced closely. Plant populations of 40, 000 to 45,000 per hectare are suggested for large-headed types while for cultivars with medium-sized heads, populations of 55,000 to 65,000 plants per hectare are said to be ideal. For baby cabbage, populations of 80,000 to 100,000 plants per hectare are recommended. It is recommended that large-headed cultivars should be planted 600 to 700 mm apart between rows and 450 mm apart within rows. Smaller-headed varieties are planted 600 X 300 mm apart.

Fertilisation

Cabbage is a heavy feeder and requires supplemental fertilisation in the form of manure or compost, nitrogen, phosphorus and potassium. Fertiliser programmes should be based on soil analyses and should be developed for each field. Cabbage requires 200 to 250 kg nitrogen per hectare. Nitrogen is supplied in split applications, where 50  per cent to 66  per cent is broadcast and ploughed in just before planting. The first application is made together with phosphorus and potassium. The remainder is side-dressed two to three weeks after transplanting and again three weeks later or applied once-off at about six weeks.

If a fertiliser mixture is preferred, 1,500 kg of 2:3:2 (22) and 100 kg potassium per hectare may be broadcasted before planting. A top dressing of 300 kg LAN should be applied approximately four weeks after transplanting and again 4 weeks later if required.

Cabbage also needs micronutrients for proper growth and development. The crop has a high requirement of calcium and deficiencies of this nutrient may occur on acid soils, on soils with very high potassium or on very dry soils.

Foliar sprays of calcium nitrate can be used to supply calcium. Magnesium may also be deficient on acid soils, on very light soils or on soils that are very high in potassium. Spraying the plants with 5 kg magnesium per hectare can rectify the problem.

Cabbage is very susceptible to molybdenum deficiency. Plants should be sprayed with 125 g of sodium- or ammonium molybdate in 500l of water per hectare as soon as signs of deficiency are noticed. The availability of molybdenum may be increased by providing enough lime prior to planting. Iron may be applied with a foliar spray with 1 % iron sulphate or chelate. The deficiency of iron is common on calcareous, alkaline soils. Manganese deficiencies are prevalent on soils with a pH of more than 5.5. A foliar spray of 5 kg per hectare of manganese sulphate or 2 to 3 kg/ha of manganese oxide is suggested as soon as symptoms of deficiency are observed. Cabbage may have boron deficiencies in areas with high rainfall. Three kilograms of Solubor are effective in controlling boron deficiency.

Irrigation

Cabbage should be irrigated immediately after sowing or transplanting. Thereafter, irrigation should be applied at intervals of 10 to 12 days in heavy soils or eight days in light soils and the schedule should be followed until the heads are fully developed and firm. Young plants should receive enough water for vegetative growth before forming heads. Excess moisture when the heads have formed may cause them to crack.

Weed control

Weeds are controlled mechanically or by hand as well as chemically through the application of registered herbicides. Mechanical cultivation should be done during land preparation until the plants are about half-grown. The first cultivation should be done two to three weeks after transplanting.

Pest control

Aphids (several kinds)

Cabbage is attacked by several aphids but the grey cabbage aphid (Brevicoryne brassicae) and the green peach aphid (Myzuspersicae) are the most common. Damage is caused when they suck sap from the plant and contaminate the edible product. Feeding of the cabbage aphid causes a chlorosis and malformation of the leaf.

aphids

Diamond-black moth (Plutellaxylostella)

They suck sap from tender growth, resulting in a whitish, scarred appearance. Growth and yields can be seriously reduced by heavy infestation.

Bagrada bug (Bagradahilarus)

They suck sap from tender growth, resulting in a whitish, scarred appearance. Growth and yields can be seriously reduced by heavy infestation.

American bollworm (Helicoverpaarmigera)

The larvae feed on the leave. They cause severe damage in the early stages of growth by destroying the growing points of the plants.

Cabbage webworm (Helula spp.)

The larvae spin a thin web over their feeding places. Damage is severe during early attacks when they destroy the growing point of the plants.

Greater cabbage moth (Crocidolomiabinotalis)

The larvae spin a thin web over their feeding places. Damage is severe during early attacks when they destroy the growing point of the plants.

Red spider mite

Red spider mites are found on the underside of leaves, where they weave a fine web. Damage is caused by sucking, resulting in a bronzing and yellowing of leaves.

Cutworm (Agrotis spp.)

Cutworms cause damage when they cut off the stems of young seedlings close to ground level.

Thrips

Thripstabaci is the most common species on cabbage. High populations of the insect contaminate the edible product, thus affecting its appearance or quality.

 

General control measures

Control measures such as crop rotation, using resistant cultivars, using registered chemicals

  • Sterilising the seedbed before planting
  • Removing infected plants when symptoms appear
  • By crop rotation
  • Planting on ridges or raised beds
  • Good water management aimed at keeping the soil dry
  • Grow transplants in fumigated beds
  • Lime the soil
  • By planting resistant cultivars
  • Use containerised seedlings.
  • Do fungicide treatment of seedbed.
  • Seedbeds should be situated far from old production fields.
  • All debris should be removed after harvesting.

 

 Harvesting maturity

The crop is harvested when the heads attain their full size and become firm and hard but tender. The colour of the head is sometimes used as a maturity index. A fully developed head has a lighter shade of green. The crop for pickling should be harvested when the cover leaves curl back, and the white leaves beneath are exposed. If harvesting is delayed, the heads may split and rots may occur while the heads harvested early may be soft.

 

 Post-harvest handling

Harvested produce should always be removed from direct sunlight and transported to the packing shed as soon as possible. Cabbage and leafy greens are particularly susceptible to wilting and other damage from high temperatures.

When there is a delay of more than an hour or two between harvest and packing, a water drench or spray arrangement can help prevent dehydration and overheating.

 Transport

Care must be taken that trucks are not overloaded on the bottom layers of produce are crushed.

 

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