Watermelons are cold-tender plants that require long growing seasons to produce large, healthy crops. Most watermelon plants take 85 days or longer to mature, but some early-season varieties can be ready for harvest in just 70 to 75 days. Two main types of watermelons are available; seedless watermelons and normal seed types. Seedless watermelons are self-sterile hybrids, meaning that they must be grown beside normal seed types to produce fruits. Seedless types tend to produce sweeter melons and more vigorous vines, because the plants direct more energy into these areas than into producing seeds.
Plant your watermelons after all chance of frost has passed and the soil has warmed. Choose a planting location that has sandy, loamy soil and full sunlight. Space the watermelon plants 6 feet apart in rows of hills spaced 7 to 10 feet apart.
Water your watermelon plants deeply by soaking the soil to a depth of 6 to 12 inches around the plants. Water once or twice each week only during drought conditions or prolonged dry spells.
Keep your watermelon plants free of weeds by hoeing shallowly around the plants or hand-pulling the weeds. Avoid hoeing deeply so that you don't damage the watermelon's roots.
Harvest the watermelons when the fruit's skin feels rough and very firm, the bottom of the watermelon turns yellowish, the tendrils attached to the stem turn brown and dry, and the fruit's skin color turns dull.