Watermelon Production Guide

General

Watermelons are mainly grown outdoors. To supply the early market, low plastic tunnels can be used to advance production by creating a suitable microclimate and raising soil temperatures.

Climate Requirements

The minimum soil temperature for good germination is about 18°C, with an optimum range of 30°C to 35°C. Germination is poor below 15°C, and such low temperatures also retard root growth. Watermelons are sensitive to frost. Little to no growth occurs below 15°C, while growth is rapid between 18°C and 30°C. Plants thrive at higher temperatures, but relatively low temperatures combined with short daylight hours encourage the formation of more female than male flowers. Conversely, at very high temperatures (35°C or more), mainly male flowers are produced.

Poor pollination of female flowers occurs when temperatures fall below 15°C, while higher temperatures tend to promote pollination. High atmospheric humidity—especially during later growth stages—favours the development of fungal diseases. Prolonged cool, cloudy, or moist weather during flowering reduces bee activity, often leading to poor pollination and a lower fruit set.

Soils

The ideal soils for watermelon are sandy loam to loam, with a clay content of 15% to 30%, and well-drained to a depth of at least 900 mm. A minimum soil depth of 450 mm is required. Heavier soils remain damp for too long and may promote fruit rot.

Plant Spacing & Seeding Rates / HA

Recommended spacing: 500 mm x 1.8–2.5 m. Seed requirement: 3–4 kg/ha. Placing windbreaks to protect the crop is beneficial. Fruit set is improved by placing beehives in the field (3–4 hives per hectare).

Time of Planting

Watermelons do not transplant easily and are therefore usually direct-seeded. Typically, 2–4 seeds are sown per station, with excess plants later thinned out. Occasionally, seedlings (speedlings) are used, particularly for squashes and marrows, to achieve earlier crops in cooler areas. Seeding rates for this purpose vary from 1–3 kg/ha.

In cooler regions, planting should be delayed until after the last frosts, when the soil has warmed to at least 18°C. The crop should be harvested before the first winter frosts.

Irrigation

Keep the soil moist until the crop emerges. To encourage deep rooting, maintain soil moisture during the first third of the growing period so that whenever 90% of available moisture is depleted, the soil is re-wetted to a depth of 450 mm. After this stage, allow only 50% depletion before irrigating, wetting the soil to a depth of 600 mm.

Adequate watering from flowering onwards is essential. Avoid irrigation immediately before harvest, as it negatively affects fruit quality.

Harvesting

Harvest watermelons just before they reach full maturity; they will ripen sufficiently during transport. To ensure quality, harvest early in the morning to avoid field heat. When storing under controlled conditions, maintain temperatures above 10°C to prevent chilling injury.

Harvesting

Diseases

Pests

Weeds