Watermelon is a warm-weather fruit that has a tender flesh and is quite sweet, with a high water content. Almost all areas of the United States have weather appropriate for the growth of watermelon, although warmer areas fare better in crop production. The large watermelon is started from a small seed.
Watermelon seeds are planted after the danger of frost has passed. Daytime temperatures for watermelon seed germination are between 70 and 80 degrees Fahrenheit, with nighttime temperatures between 65 and 70, says Ohio State University.
Starting the Seed
Seeds are best started inside three weeks before they are planted outside, says the University of Illinois. Two to three seeds are planted in a peat pellet, peat pots or cell packs and moistened to germinate the seed. The best plants are kept while weaker ones are thinned out. Expensive seeds, such as those of the seedless watermelon varieties, are planted one to a cell.
Transplanting the watermelon seedling to the outside garden requires care. The seedling requires hardening off by being placed outdoors for longer times each day until it is used to the outdoor weather. This prevents shocks to the system. Transplants are removed from the seed tray with a knife or a spatula to prevent damage to the roots, says the University of Missouri. The seedling is planted at the same depth outside as inside.
Seeding outdoors is possible in temperate regions with consistent spring temperatures. Seeds are placed in small dirt hills one inch deep and six feet apart. The hills are spaced seven to 10 feet apart to allow room for the watermelon vines to grow. Transplants are placed two to three feet apart in the rows.
Weeds require immediate removal to prevent competition for resources with the young watermelon plant. Watermelon plants have deep roots, says the University of Illinois, and rarely require watering unless there are long periods of drought. Harvest of watermelons is necessary when the vine attached to the watermelon turns brown and curls, the fruit surface color turns dull, the skin becomes hard, and the bottom of the melon turns yellow.