ABC of growing the juiciest watermelons

Some farmers must have made excellent use of the last few hot months by growing watermelons (Citrullus lanatus).

Watermelons do very well in hot and even arid regions. Exposure to sun and high temperatures ensure the desired red colour and sweet taste when fully ripe. Return on investment is about Sh60,000 an acre. But how do you achieve this?

Start by choosing the right site. It has to be in full sun in a warm lowland area. Go for a light but fertile and well-draining soil with a pH of 5.5 to 6.8. Three weeks before planting, prepare 1m by 1m mounds, about 25cm high, by mixing high quality compost, chicken manure and topsoil.

Leave enough space between rows of the mounds. Make a shallow indent at the top of each mound and plant three seeds directly into each mound, about 1cm deep.

FIVE DAYS

Water thoroughly at the top of the mound so that it can soak slowly without running off the sides. Mulch the entire mound with grass or straw.

Choose a variety that is resistant to wilt, for example, Charleston Gray or Crimson Sweet. Other varieties are the high-yielding Sukari F1, Sugar Baby, which is a smaller but very sweet variety, and Zuri F1.

Seedlings usually emerge after five days. Thin out the latest and smallest developing seedlings to leave enough space for two big and healthy plants per mound. Water the mounds regularly until the vines start setting fruits. Do not let the plants be so waterstressed that the leaves collapse. But also avoid overwatering and wetting the leaves when watering. After the fruit sets, let the soil dry before watering again and towards harvest, watering should stop completely to increase the sugar content.

Yield in watermelons depends highly on pollination by bees. Therefore, it is recommended to place a beehive per each acre. This also means that use of pesticides should be minimised to avoid killing pollinating insects. Control of whitefly, aphids and fruit flies can be done by placing yellow and blue sticky traps in the entire field. This way, the number of pests are reduced.

If it’s necessary to spray, it should be done at night when bees are not flying. If no beehives are available, bees can be attracted by providing water sources in shallow dishes around the field.

Watermelons produce male and female flowers. Only the female will bear fruits, the male ones drop after a few days. But both male and female flowers are needed for pollination. The male flowers appear first, followed by the female, which only open for a day. If they are not pollinated then, they will not bear fruit.

To yield three to five melons per plant, it is critical that pollination is successful. Female flowers can be identified by the small round swelling underneath the bloom, which will later develop into a fruit. This is absent in male flowers. If more than five fruits set on a plant, they should be removed as they will end up to be too small.

Powdery mildew appears as a white film on top of the leaves, while downey mildew forms on the underside. They are promoted by high differences between day and night temperatures and easily attack stressed plants. Mildew can quickly destroy the entire leaves mass of watermelons and needs to be monitored regularly. Copper-based pesticides can be used as a prevention. For Downey mildew, it is important that the chemical is also applied to the undersides of the leaves.

SHARP KNIFE

If you applied compost and manure before planting, using inorganic fertiliser would not be necessary unless indicated so by a soil test. Weeding should be done by pulling weeds by hand to avoid disturbing the roots of the plants. Watermelons reach maturity after 75 to 100 days.

Cut fruits of the stems with a sharp knife or shear. They are ripe when the white spot that develops where the melon touches the ground turns yellow. If harvested too early, it will be tasteless and colourless. Harvested too late or stored for too long, the flesh will ferment and turn mushy.

They should be stored cool if possible. Yields of 20 tonnes and above per acre are common.

Ms Weber is the country manager SoilsCare. [email protected]