Watermelons prefer rich, well-drained soil. Before planting, incorporate organic matter and fertilizer. Sow seeds in warm soil, about 1-2 inches deep, spacing mounds 4 feet apart. Thin mounds to two plants once seedlings emerge. If you use black plastic mulch, transplant seedlings 2 feet apart for earlier maturity. Deep, infrequent irrigation helps develop strong plants, while plastic and organic mulches conserve water and reduce weeds. Mulches should only be applied once the soil warms to 75°F.
Watermelon Varieties
Large red-fleshed watermelons like Crimson Sweet and Mirage Hybrid weigh between 15-25 lb. Mickylee and Minilee are icebox types, weighing around 10-15 lb. Golden Crown and Yellow Baby are yellow-fleshed varieties. Many other watermelon varieties, available locally or through seed catalogs, also grow well in Utah.
How to Grow Watermelon
Watermelons thrive in organic, well-drained, sandy soils. However, most soil types will support watermelon growth if they are well-drained.
Soil Preparation
A site receiving full sun should be selected. Fertilizer needs can be determined by soil testing. The recommended fertilizer should be worked into the top 6 inches of soil. If compost is used, no more than 1 inch of well-composted organic matter should be applied per 100 square feet.
Plants
Watermelons can be started from seed or transplants. Seeds should be planted 1-2 inches deep, while transplants should have 2-3 leaves and well-developed roots. A six-week period is necessary for growing transplants, which mature about two weeks earlier than seeded melons, and are recommended for short growing seasons.
Planting and Spacing
Watermelons should be planted after the soil has warmed to 65°F or when the danger of frost has passed. Seeds are planted 4 feet apart in mounds, and thinned to two plants after two leaves appear. Transplants should be spaced 2 feet apart with rows 4-6 feet apart. Root damage during planting should be avoided to ensure quicker establishment.
Mulch
Black plastic mulch can be used to warm the soil, conserve water, and control weeds, allowing earlier planting and maturity, especially with transplants. Once the plastic mulch is laid, holes should be cut for seeds or transplants. Organic mulches should not be applied until soil temperatures exceed 75°F. Both plastic and organic mulches help with water conservation and weed control.
Row Covers
Row covers can enhance growth and promote early development. Devices like hotcaps, plastic tunnels, or fabric covers protect seedlings and transplants from cold air. When air temperatures exceed 80°F, ventilation is required. The covers should be removed when flowering begins or when temperatures surpass 90°F.
Irrigation
Deep, infrequent watering is recommended, with 1-2 inches of water provided weekly. Drip irrigation is preferable, and mulching around the plants will conserve moisture and reduce weeds. Less water should be applied as fruits ripen to enhance flavor.
Fertilizer
Once vines have runners, 3-4 tablespoons of nitrogen fertilizer (21-0-0) should be applied around each plant and watered in.
Weed Control
Weeds can be effectively controlled using plastic or organic mulches. Vigorous vine growth will also naturally smother weeds.
Insects and Diseases
Common insect pests include aphids, which feed on leaves, and cucumber beetles, which damage vines and transmit diseases. Various diseases such as powdery mildew and wilt disease can affect watermelon crops. Visit the Utah Pests website for more information on control methods.
Harvesting and Storage
Watermelons take 35-45 days to mature after flowering. Ripeness can be identified by the browning of the curly tendril opposite the fruit, the yellowing of the ground spot, and the dulling of the skin. Once harvested, watermelons can be stored at 45-50°F for 1-2 weeks.
Watermelon Productivity
Around 3-4 plants per person are recommended for fresh consumption, with an additional 3-4 plants needed for juicing or freezing. Expect about 40 fruits per 100 feet of row.
Watermelon Nutrition
Watermelons are mostly composed of water. A two-cup serving provides 80 calories, is low in fat, and is an excellent source of vitamins A and C.
