The watermelon is a tender, warm-weather annual. Watermelons along with muskmelons and cantaloupes are sometimes called summer melons.
• Sow watermelon seed in the garden or set out transplants 3 to 4 weeks after the last average frost date in spring.
• Start watermelon seed indoors about 6 weeks before transplanting seedlings into the garden. Start seed indoors in 4-inch or larger biodegradable peat or paper pots that can be set wholly into the garden so as not to disturb the roots.
• Watermelons require 65 to 90 frost-free days to reach harvest.
About Watermelons. The watermelon is a long-trailing annual plant. Watermelons can be solid green or striped green and white. Watermelons can be oval, oblong, and round. Fruits can weigh from 10 or 15 pounds to more than 100 pounds and are commonly 30 pounds or more. The watermelon has a thick, solid rind with sweet, succulent flesh that can be pink, red, yellow, orange, or grayish white. Male and female flowers appear on the same vine.
Watermelon Yield. Grow 2 watermelon plants for each household member.
Site. Plant watermelons in full sun. Watermelons grow best in loose, well-drained, but moisture-retentive soil rich in organic matter. Add aged compost to the planting bed before planting. Melons prefer a soil pH of 6.0 to 6.8.
Watermelon Planting Time. Sow watermelon seed in the garden or set out transplants 2 to 3 weeks after the last average frost date in spring. Start watermelon seed indoors about 6 weeks before transplanting seedlings into the garden; start seed in biodegradable peat or paper pots at least 4 inches in diameter that can be set wholly into the garden so as not to disturb roots. (This is recommended in short growing season regions where the soil warms slowly in spring.) Melon seed will germinate in 10 days at 65°F. Watermelons grow best in air temperatures ranging from 70° to 90°F. Avoid growing watermelon where night temperatures dip below 50°F; this will cause fruit to lose flavor. If temperatures exceed 90°F for several days, flowers will drop without setting fruit. Watermelons require 65 to 90 frost-free days to reach harvest and will tolerate no frost. In cool or short-season regions, grow smaller varieties that come to harvest quickly.
Planting and Spacing Watermelon. Sow watermelon seed 1 inch deep. Sow 4 to 6 melon seeds in mounds or inverted hills 24 inches across; thin to the 2 or 3 strongest seedlings in each hill when seedlings have developed three or four true leaves (or set 2 or 3 transplants in each hill). Cut the thinned seedlings at soil level with scissors. Space mounds or inverted hills 6 feet apart. Mounds can range in height from a few inches to more than 12 inches tall; mounds will allow vines to run away down the slope. Use inverted hills where the weather and soil are very dry and plants will benefit from the collection of rain or irrigation water. Make an inverted hill by removing an inch or two of soil to from a circle 24 inches across; use this soil to make a rim around the circle. The rim also will protect young plants from heavy rains that might wash away the soil leaving shallow roots exposed. More tips: Watermelon Seed Starting Tips.
Water and Feeding Watermelon. Watermelons are 95 percent water. They require plentiful regular, even watering for quick growing. Keep the soil moist until fruit reaches full size then stop watering while the fruit ripens. Mulch to retain soil moisture. Avoid watering plants overhead which can result in mildew. Prepare planting beds with aged compost; add aged manure to beds the autumn before planting. Side dress melons with compost or manure tea every 2 to 3 weeks during the growing season.
Companion plants. Corn, radish, beans, nasturtium.
Watermelon Care. Encourage watermelon plants to set three or four fruits at the same time; if a plant sets one fruit early, pinch it out to encourage the plants to develop several fruits at the same time. One fruit off to a head start can suppress all further fruiting on the vine until the fruit matures. Pinch back multiple flowers to permit just a few fruits to form on each vine. If flowers die without setting fruit, they are probably male flowers, which do not produce fruit; each plant produced both male and female flowers.
Cultivate carefully around vines until they cover the ground and smother out competing weeds. Support melons on a low tripod or A-frame trellis to keep them off wet ground; use netting or a bag to support trellis-grown melons. For sprawling watermelons, place a board under each melon to keep the fruit clean and dry. Regular, even watering will help fruits avoid blossom-end rot which is caused by fluctuation of soil moisture. More tips: How to Grow Watermelon for Best Flavor.
Container Growing Watermelon. Watermelons are usually too large to grow in a container. Select a bush, dwarf- or mini-cultivar to grow in a container. Place a trellis or other support next to the plant to save space and increase yields. Choose a container at least 18 inches deep that can support a vining plant. In short growing season regions extend the season by starting melons indoors and moving them out when the weather has warmed.
Watermelon Pests. Aphids and cucumber beetles will attack melons. Hose away aphids with a blast of water or pinch out infested foliage. Hand pick and destroy cucumber beetles promptly; they can transmit cucumber bacterial wilt to melons.
More tips: Melon Growing Problems: Troubleshooting.
Watermelon Diseases. Watermelons are susceptible to anthracnose and bacterial wilt. Planting disease resistant varieties when they are available and maintaining the general cleanliness and health of your garden will help cut down the incidence of disease. Do not handle the vines when they are wet. If a plant does become infected remove it before it can spread disease to healthy plants.
Bacterial wilt which is spread by cucumber beetles can cause watermelon plants to suddenly wilt and die just as they begin to produce fruit. Control cucumber beetles as soon as they appear.
Anthracnose is a soil-borne fungal disease that can cause leaf spots, leaf drop, wilting and sometimes death. Keep the garden clean and plant disease resistant varieties. Remove diseased plants from the garden immediately.
Harvest Watermelon. Watermelons will be ready for harvest 65 to 90 days after sowing. When watermelons are ready for harvest the vine’s tendrils will begin to turn brown and die off. A ripe watermelon will make a dull sound when thumped. The soil side of a watermelon will turn from white to pale yellow when the fruit is ready for harvest. Ripe melons will have a sweet aroma at the stem end. Limit water for a week in advance of harvest to concentrate sweetness.
Storing and preserving. Watermelons will keep in the refrigerator for up to one week, but sweetness and flavor may diminish. It takes about 12 hours to chill a large watermelon. Watermelons can be kept in a cool, moderately moist place for 2 to 3 weeks without refrigeration. Melon flesh can be frozen and rinds can be pickled.
More tips: How to Harvest and Store Watermelon.
• Icebox size watermelons: Early Midget (65 days); Garden Baby (70 days); Golden Midget (65 days); Sugar Baby (68-96 days); Tiger Baby (80 days).
• Oblong, green rind: Northern Sweet (68 days).
• Oblong, grayish rind: Allsweet (100 days); Calsweet (92 days); Charleston Gray (90 days); Desert Storm (80 days); Fiesta (85 days); Regency (82 days); Royal Majesty (80 days); Sangria (85 days); Strawberry (85 days); Sun Sweet (85 days); Sweet Favorite (64-79 days).
• Round, green: Black Diamond (75-95 days); Black Diamond Yellow Belly (90 days); King and Queen (80-90 days); Moon and Stars (100 days).
• Round, striped: Crimson Sweet (80-96 days); Navajo Sweet (90 days); Super Sweet (90 days).
• Giant sized: Carolina Cross (100 days).
• Space savers: Bush Sugar Baby (80 days); Garden Baby (75 days); Petite Sweet (75 days); New Hampshire Midget (77 days); Sugar Baby (79 days).
• Yellow or orange flesh: Arikara (85 days); Yellow Doll (75 days).
More varieties to grow: Watermelons for Home Gardens: Top 12 Varieties.
Common name. Watermelon
Botanical name. Citrullus vulgaris
Origin. Tropical Africa