Watermelons are warm weather crops and they require long growing season of high temperatures. Good vegetative growth requires 18-32oC, the optimal being 18-24oC. They do better with adequate water supply.

Within a growing season, at least 400mm of moisture will be required. Soils should be well-drained and with good waterholding capacity. The pH should be 6.0-6.8.

Watermelons have been grown successfully in sandy soils, where water supply is adequate. However, the best soils are sandy loam or silt loam. Application of nitrogenous fertilisers is based on soil type. Soils with high organic matter require 80kg N/ha, while light soils require 140kg N/ha.

The nitrogen fertiliser should be applied and incorporated into the soil at planting time. Phosphorus and potassium applications are based on soil tests, and both should also be applied at the time of planting. The best melons are those raised under irrigation.

Most of the soils under which the melons are grown are light, which require frequent watering to maintain good growth.

Depending on the environmental conditions, 450-600mm of water is required within a growing season. Water can be applied through drip or furrow irrigation.

Use of sprinkler irrigation raises the humidity within the canopy and this leads to increased disease incidences. Weeds should be controlled, especially when the melon plants are young.

Weeds offer greater competition by shading the melon plants. Weed control can be achieved by application of black plastic mulches, cultivation, and use of herbicides that are registered for use in melons.

Pests and diseases: Diseases such as powdery mildew, downy mildew, alternaria leaf spot, anthracnose, and fusarium wilt cause problems under certain conditions.

Insect pests such as cucumber beetle, which is a vector for bacterial wilt, aphids, flea beetles, and melon worms cause problems and can be controlled using suitable insecticides.

Phytophthora fruit rot affects watermelon fruits during heavy rains. To control the disease, you should apply a fungicide when fruits start forming because the disease does not affect the leaves. Avoid planting watermelon during the periods of heavy rainfall.

Watermelons need water in the first few weeks of growth but when they start producing fruits, they need little water or if you are irrigating, you can stop.

As the fruit develops, the less water it gets, the better as this will increase the sugar content and sugar concentration in the fruit making it sweeter.

Harvesting: Watermelons are ready for harvesting in about three or four months. Maturity is indicated when the fruit gives off a hollow sound when tapped with knuckles.

The fruit stem should be cut with a sharp knife rather than broken by hand.

Carol Mutua, 
Department of Crops, Horticulture and Soils, Egerton University.