Watermelons are herbaceous vines commonly grown for their sweet, edible fruit. Watermelon plants typically grow to about 2 feet in height and the vines can reach up to 20 feet in length. Watermelons are annual plants that cannot tolerate temperatures below 50 degrees Fahrenheit. They take about 4 months to grow from seed to maturity and require routine maintenance to stay healthy and bear fruit. Watermelons are, however, grown successfully throughout the United States from seed, as long as the proper environment is provided.
Choose a planting site that receives full sunlight throughout the day. Apply a 4-inch layer of organic compost over the planting site, and use a garden tiller to incorporate it into the soil to increase drainage.
Fertilize the soil using a 16-16-8 NPK fertilizer prior to planting to further increase fertility. Spread 6 cups of fertilizer over every 100 feet of soil at the planting site and use a garden tiller to work the material into the soil.
Sow watermelon seeds after all danger of frost has passed and average daily temperatures have reached at least 65 degrees Fahrenheit. Form small mounds in the soil about 6 inches in height. Plant three seeds in each mound at a depth of 1 inch. Space each mound 4 feet apart.
Apply a 2-inch layer of organic mulch over the soil surrounding watermelons once the average daily temperature has reached 75 degrees Fahrenheit. Begin the layer of mulch at the base of the mound, so growth is not inhibited.
Water watermelons at a rate of 2 inches per week. Reduce the frequency of watering to 2 inches every 10 days once the fruit begins to ripen to enhance the flavor. Apply water directly to the soil to reduce the chance of disease.
Fertilize watermelons immediately after the vines form runners. Use a high-nitrogen 34-0-0 NPK fertilizer to promote root formation and fruit development. Apply the fertilizer at the rate recommended on the package.
Harvest watermelons about 40 days after flowering, or when the curly vine opposite the fruit is brown, the ground spot on the bottom of the fruit is yellow in color and the skin becomes dull. Pick the watermelon from the vine and store at 45 to 50 degrees Fahrenheit for up to 2 weeks.