These tasteful, watery fruits are produced on annual, tropical or subtropical plants with spreading stems that grow up to 3-4 m. The fruits, eaten raw, may be rounded or oblong, green or cream, striped or mottled, with red, pink or yellow pulp, and may grow up to 60 cm in length. Being tropical plants, they need a temperature of 25-30 Celsius degrees (77-86 F) in order to develop well and may be grown outdoors only in sunny, sheltered areas. They may also be grown under cover in areas where outdoors climate are colder.
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).