Lettuce: Healthy salad loved by urban dwellers

Lettuce (Lactuca Sativa) is an annual leaf vegetable of the aster family (Asteraceae).

Most lettuce varieties are eaten fresh and are commonly served as the base of green salads.

It is generally a rich source of vitamins K and A, though the nutritional quality varies, depending on the variety. Lettuce varieties include Brauma F1 (well suited for warm areas), Butterhead, Leaf Lettuce and Romaine. Others are Crisphead, Loose-leaf, Chinese Lettuce and Summer Crisp. Simon Gicheru, a Kiambu-based farmer, explains how to grow the crop from planting to harvesting.

Ecological requirements

A temperature of between 15 degrees to 30 degrees centigrade is the best. Although the crop can thrive in a wide range of soils, optimal production is achieved on well-drained fertile loam soils that are rich in organic matter. “It must have a good water-holding capacity and a pH of between 5.5 and 7.0,” says Gicheru.

Propagation and planting

Lettuce is propagated from seeds, which can be sown directly into the main field or raised in a nursery bed and transplanted thereafter. “It is recommended to raise seedlings in a nursery for a good start and break seed dormancy,” he says. Prepare the land well. Plough and harrow to a fine tilth and spread well rotten manure. Dig planting holes at a spacing of 30cm by 30cm. Put bottlecap (5g) per hole planting fertiliser and mix it well with soil. Plant a healthy lettuce seedling in each hole and firm soil around the base well and mulch with dry grass before watering the plant.

Routine field management 

Weeding - weed regularly until the crop can get a good ground cover and kill weeds on its own. Lettuce is a shallow-rooted crop and so weed with care.

Topdressing – do this one week after transplanting and four weeks after transplanting. Use nitrogen-rich fertiliser.

Irrigation – to supply enough moisture, you may need to water your lettuce crop, especially during dry seasons. “You can also apply mulch like dry grass to help you conserve moisture,” says Gicheru.

Crop rotation - rotate your lettuce field with crops like cereals, such as maize and legumes like beans, to reduce the build-up of pests and diseases.

Pests and diseases

Farmers should look out for pests such as the cutworm, diamond black moth, aphids and cabbage sawfly, root-knot nematodes and diseases like black rot, downy mildew, leaf spot, damping off and lettuce mosaic virus.

Harvesting

Most lettuce varieties take two to three months to be ready for harvesting from the time of transplanting. At this time, the hearts are fully developed. After maturity, the lettuce can be harvested for the next four weeks. To harvest, cut heads off with a knife. “Remove damaged or old leaves, then wash ready for use or for the market,” advises Gicheru. On average and under good management, a farmer can harvest four to six tonnes per acre.

Market

Lettuce is widely consumed, especially in urban areas. It is mostly used in making salads. Gicheru sells his produce online through referrals as well as in markets.