Watermelon is a tender, warm-season vegetable. Watermelons can be grown in all parts of the country, but the warmer temperatures and longer growing season of southern areas especially favor this vegetable. Gardeners in northern areas should choose early varieties and use transplants. Mulching with black plastic film also promotes earliness by warming the soil beneath the plastic. Floating row covers moderate temperatures around the young plants, providing some frost protection in unseasonable cold spells.
Seedless watermelons are self-sterile hybrids that develop normal-looking fruits but no fully developed seeds. The seeds for growing them are produced by crossing a normal diploid watermelon with one that has been changed genetically into the tetraploid state. The seeds from this cross produce plants that, when pollinated by normal plants, produce seedless melons.
In seedless watermelons (genetic triploids), rudimentary seed structures form but remain small, soft, white, tasteless and undeveloped tiny seed coats that are eaten virtually undetected along with the flesh of the melon. Seed production for these seedless types is an extremely labor intensive process that makes the seeds relatively expensive. Because germination of these types is often less vigorous than normal types, it is recommended that they be started in peat pots or other transplantable containers, where the germinating conditions can be closely controlled Once transplanted, cultivation is similar to that for regular watermelons.
For pollination necessary to set fruit, normal seed types must be interplanted with seedless melons. The pollinator should be distinct from the seedless cultivar in color, shape or type so that the seedless and seeded melons in the patch can be separated at harvest. Because seedless types do not put energy into seed production, the flesh is often sweeter than normal types and the vines are noticeably more vigorous as the season progresses.
In the Garden
Plant after the soil is warm and when all danger of frost is past. Watermelons grow best on a sandy loam soil, although yields on clay soils can be increased significantly by mulching raised planting rows with black plastic film.
Watermelon vines require considerable space. Plant seed one inch deep in hills spaced 6 feet apart. Allow 7 to 10 feet between rows. After the seedlings are established, thin to the best three plants per hill. Plant single transplants 2 to 3 feet apart or double transplants 4 to 5 feet apart in the rows. Start the seeds inside 3 weeks before they are to be set out in the garden. Plant 2 or 3 seeds in peat pellets, peat pots or cell packs and thin to the best one or two plants. For expensive seedless types, plant one seed to a pot or cell and discard those that do not germinate. Do not start too early – large watermelon seedlings transplant poorly. Growing transplants inside requires a warm temperature, ideally between 80 and 85°F. Place black plastic film over the row before planting. Use a starter fertilizer when transplanting. If you grow seedless melons, you must plant a standard seeded variety alongside. The seedless melon varieties do not have the fertile pollen necessary to pollinate and set the fruit.
In the Kitchen
Wash whole watermelons with clean water before slicing to remove potential bacteria. The flavor of watermelon is best enjoyed raw. Heating diminishes the flavor and softens the texture. Watermelon tastes best icy cold in fruit smoothies, slushes or simply eaten from the rind. To make melon balls, cut the watermelon in half lengthwise then into quarters. Watermelon balls can be scooped right out of rind. Create perfect balls, using a melon baller, and a twist of the wrist. The watermelon shell can be used to hold the melon balls as well as other fruit. Watermelon punch is also served from the hallow rind. By sitting the round end inside a ring or bowl, the shell will remain stable during serving. To remove seeds, cut each quarter in half again. With the flesh of each wedge on top and the rind sitting on the counter, look for the row of seeds along the flesh of each wedge. Using a sharp knife, cut along the seed line and remove the flesh just above it. Scrape the seeds from the remaining piece.
Seeded watermelon chunks can be frozen to use in watermelon slushes or fruit smoothies. Watermelon sorbet or granita stays fresh in the freezer for up to 3 months. The difference between a sorbet and a granita is in the texture. Sorbets are smooth, whereas granitas are coarse. You do not need an ice cream maker to make a granita. The best way to enjoy watermelon is while they are fresh and sweet.