The watermelon is a tender, warm-weather annual. Watermelons along with muskmelons and cantaloupes are sometimes called summer melons. Grow watermelons in the warmest, frost-free time of the year.
- 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.
Where to Plant Watermelons
- Plant watermelons in full sun.
- Watermelons grow best in loose, well-drained, but moisture-retentive soil rich in organic matter.
- Add aged compost and aged manure or a commercial organic planting mix to the planting bed before planting. Turn the soil to 12 inches (30cm) deep.
- Melons prefer a soil pH of 6.0 to 6.8.
- Plant watermelons on hills or mounds or on raised rows. Solar heat hitting the soil on a mound or raised row will keep plants and roots warm.
- Create a mound 6 to 12 inches (15-30cm) high and 5 feet (1.5m) across.
- If planting in ground-level beds, warm the soil in advance of planting by laying black plastic sheeting on the bed two weeks before planting.
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.
- Garden soil temperature should be at least 70°F (21°C) at planting time. Pre-warm the soil by placing black plastic sheeting over the planting bed for two weeks prior to planting.
- To get a head start on the season and in short growing season regions, 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 (10cm) in diameter that can be set wholly into the garden so as not to disturb roots.
- Watermelon seed will germinate in about 10 days at 65°F (18°C), sooner in warmer soil.
- Watermelons grow best in air temperatures ranging from 70° to 90°F (21-32°C).
- Avoid growing watermelon where night temperatures dip below 50°F (10°C); this will cause the fruit to lose flavor.
- If temperatures exceed 90°F (32°C).
- for several days, flowers will drop without setting fruit.
- Watermelons require 65 to 90 frost-free days to reach harvest depending on the variety.
- Watermelons will tolerate no frost. In cool or short-season regions, grow smaller varieties that come to harvest quickly.
Planting and Spacing Watermelons
- Sow watermelon seed 1 inch (2.5cm) deep.
- Sow 4 to 6 melon seeds on a mound or hill.
- Germination will occur in about 10 days when the soil is 70°F (21°C).
- Thin to 2 or 3 strong seedlings on each hill when seedlings have developed three or four true leaves. Cut the thinned seedlings at soil level with scissors so as not to disturb the roots of the remaining seedlings.
- Space mounds or hills 5 to 6 feet (1.5-1.8m) apart.
- Mounds can range in height from a few inches to more than 12 inches (30cm) tall; mounds will allow vines to run away down the slope. You can train vines to circle the mound.
- If you are growing watermelon in rows space plants 4 to 5 feet apart (1.2-1.5m) and space rows 6 feet (1.8m) apart.
- Grow 2 watermelon plants for each household member.
Growing Watermelons Vertically
- Watermelons can be grown up a trellis.
- Use a trellis at least 8 x 8 feet (2.4m) wide or wider. Make sure the trellis is well-anchored.
- Space plant at the base of the trellis 3 to 4 feet (.9-1.2m) apart.
- Train vines up the trellis; secure the vines to the trellis with elastic garden tape.
- Support melons growing the trellis with netting.
- You can also grow watermelons on an A-frame trellis. Lean two trellises together, tie them at the top, and anchor the base of each trellis.
Container Growing Watermelons
- Watermelons are usually too large to grow in a container.
- Select a bush, dwarf- or mini-cultivar to grow in a container.
- Chose a container that is at least 18 inches wide and deep to grow one watermelon.
- In short growing season regions extend the season by starting melons in containers indoors; move them outdoors when the weather has warmed but be careful not to pinch or break the vines.
Watering Watermelons
- Watermelons are 95 percent water. They require plentiful regular, even watering for quick growing.
- Give watermelons 1 to 2 inches (2.5.-5cm) of water every week (1 inch equals 16 gallons/60.5 liters.)
- Keep the soil moist until the fruit reaches full size then stop watering while the fruit ripens.
- Mulch to retain soil moisture. Spread straw or dried chopped leaves around watermelon plants after the soil has warmed. You can also lay black plastic sheeting or garden fabric across the planting bed. Cut an x-slot in the fabric to plant.
- Water at the base of plants with a soaker hose or drip irrigation. Wetting the foliage will leave plants susceptible to fungal diseases such as powdery or downy mildew.
- Keep the soil evenly moist during flowering and fruit development. A week or so before harvest cut back on water; dry soil will help plants concentrate sugars in the fruit.
- If leaves are wilted in the morning, the plants need water. Wilting leaves at the end of the day is not uncommon.
Feeding Watermelons
- Prepare planting beds with aged compost and aged manure or a commercial organic planting mix. Turn the soil to 12 inches (30cm) deep.
- Add several inches of aged manure across planting beds the autumn before planting.
- Side dress watermelons with compost or manure tea or a dilute solution of fish emulsion every 2 to 3 weeks during the growing season.
- Watermelons can be side dressed with an even organic fertilizer such as 10-10-10 early in the season but once flowers and fruit appear, reduce nitrogen and increase phosphorus and potassium; use a 5-10-10 fertilizer.
Companion Plants for Watermelons
- Plant watermelons with corn, radish, beans, and nasturtiums.
Watermelon Pollination
- Watermelon plants produce both male and female flowers.
- Male flowers appear a week or two in advance of the female flowers. Male flowers attract bees that are needed for pollination once female flowers appear.
- Female flowers will have a small bulge at the stem end of the flower. This bulge is an embryonic fruit.
- Some male flowers will die and drop before female flowers set fruit.
- You can hand pollinate watermelon flowers using an artist’s bristle brush. Rub the brush in the male flower to collect pollen then rub the brush in the center of the female flower to transfer the pollen.
- You can attract bees to your garden by planting flowering herbs such as dill, borage, and lavender nearby.
Caring for Watermelons
- Early in the season cover plants with a floating row cover. This will keep insects away and hold warm air around plants. Once plants begin to flower, remove the row cover during the day so that bees can get to the flowers.
- 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 plant to develop several fruits at the same time. One fruit off to a head start can suppress all further fruiting on the vine until that fruit matures.
- Cultivate carefully around vines until they cover the ground and smother out competing weeds.
- Mulch around watermelons with straw, dry chopped leaves or set down black plastic or garden fabric. Mulch will keep down weeds and conserve soil moisture.
- For sprawling watermelons, place a tile, wooden shingle, or a piece of plastic under each melon to keep the fruit clean and dry and to store solar heat which will help ripen fruit.
- About 50 days before the first expected autumn frost, remove all new blossoms from a plant; this will allow the plant to concentrate its energy into the development and ripening of fruit already on the plant.
Watermelon Pests
- Aphids and spotted and striped 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. You can also control cucumber beetles by spraying insecticidal soap, neem oil, or dusting with kaolin.
Watermelon Diseases
- Watermelons are susceptible to anthracnose, Alternaria leaf spot, bacterial wilt, and powdery and downy mildew.
- 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; this can spread fungal diseases.
- If a plant does become infected remove it before it can spread the 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.
- Powdery mildew and other fungal diseases can be prevented and slowed by spray-misting plants with compost tea or a solution of 1-part skim milk and 9-parts water.
Harvesting Watermelons
- Watermelons will be ready for harvest 65 to 90 days after sowing depending on the variety.
- When watermelons are ready to harvest vine tendrils will begin to turn brown and die off. If the tendrils are green the melon is not ripe.
- A ripe watermelon will make a dull hollow 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 the harvest to concentrate sweetness.
- Watermelons on a single plant will all be ready for harvest over a two week period.
- Use a sharp knife or garden pruner to cut the watermelon away from the vine.
- Watermelons do not continue to ripen off the vine.
Storing and Preserving Watermelons
- Watermelons will keep in the refrigerator for up to a week if not cut or sliced, but sweetness and flavor may diminish.
- A cut watermelon will keep in the refrigerator for about 4 days. Wrap the melon tightly in plastic to prevent cold burn or dehydration.
- 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.
Watermelon Varieties to Grow
- 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.
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. Fruits 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.
- Botanical name: Citrullus vulgaris
- Origin: Tropical Africa
