They prefer a well-drained, sandy loam soil with medium nitrogen levels and a pH of 5.5-7. Soil fertility is also important so you should incorporate well-rotted manure and a general-purpose fertilizer into the soil before planting.
Sow seeds in early spring under cover in trays or 6-9 cm pots at a temperature of at least 22-25 Celsius degrees (72-77 F). When seedlings reach 10-15 cm tall harden them off then plant them out after all risk of frost has passed. Plant young plants outdoors or under cover at least 1 m apart one from another. If planted outdoors protect them from wind and cold weather with plastic screens. Being extremely vigorous plants, watermelons are not normally grown in a greenhouse but under plastic covers. Remove covers at flowering time to reduce humidity and to encourage insect pollination.
Mulch the plants to retain moisture and apply a balanced fertilizer or a liquid feed every two weeks until the fruits begin to develop. Pinch out the growing points of the main shoots when they are 2 m long and reduce the sub-lateral growth from the sideshoots to two or three leaves after fruits start to develop. Train sideshoots between other plants in the row. To protect the fruits from soil-borne pests and diseases is best to place a pad of dried grass or a block of wood beneath each fruit.
Harvest the fruits after 11-14 weeks after sowing. Mature fruits give a hollow sound when tapped. They may be stored for 14-20 days at 10-12 Celsius degrees (50-54 F).