Sweet, juicy homegrown watermelons capture the magic of summer with explosive taste that doesn’t compare to their store-bought cousins. Like their cantaloupe cousins, watermelons demand 2 to 3 months of heat to produce ripe fruit, which makes growing them in northern regions challenging but not impossible. By using plastic mulch to warm soil and floating row covers to trap warm air near plants, gardeners in any part of the country can count on cutting into the homegrown goodness of watermelons.
Nutritionists have found that watermelon should be in most people’s diets because of all the health-promoting vitamin C and antioxidants—including beta-carotene and lycopene—in every bite, combining great taste with excellent nutrition. With no cholesterol and nearly no fat, serving watermelon for dessert is a wise idea.
Watermelon needs warm soil. Don’t tuck plants into the garden until soil temperature is above 70 degrees F, which typically occurs about the time peonies bloom in northern zones. To be safe, wait until at least 2 weeks past your area’s last frost date. Prior to planting, cover soil with black plastic to hasten soil warming.Because watermelons are heavy feeders, prepare your planting bed by adding seaweed, compost, or rotted manure. For best nutrient uptake, the soil pH should be between 6 and 6.8, although the plants will tolerate a pH as low as 5. If you live near a horse farm, another option that works well is to excavate the soil 1 foot deep, add a 9-inch-thick layer of fresh manure, and then cover that with 3 inches of soil mixed with compost. This creates a bed with a high-nitrogen soil base that’s naturally warm. Some gardeners even plant melons in their compost piles to ensure a warm footing and adequate nitrogen.
Give watermelon vines plenty of room to roam by spacing transplants 6 feet apart in rows 6 feet apart. If you’re growing Sugar Baby watermelon, which yields small fruit (8-10 pounds) on tidy vines, space transplants 4 feet apart. After transplanting, cover plants with floating row covers to exclude insects and trap warm air near plants.
Watermelon vines bear male and female flowers. Don’t be alarmed when the male flowers, which open first, fall off shortly after they open; they are followed by female blossoms about a week later. The female flowers, which have a small swelling at the base of the flower, stay on the vine to bear fruit. When vines start to bear both male and female flowers, remove row covers.
Tackle weeds before vines start to run because it will be difficult to move among vines at a later stage without crushing them. Mulching soil under vines suppresses weeds and slows moisture evaporation from soil.
Water plays an important role in keeping vines healthy and producing delicious fruit. Vines are most sensitive to drought during the time from transplanting to when fruits start to form. Avoid overhead watering. Soaker hoses or drip irrigation deliver water directly to soil, preventing possible spread of fungal diseases among wet foliage. Keep soil consistently moist, but not waterlogged, which will kill plants. It’s typical for leaves to wilt under midday sun, but they shouldn’t remain wilted into evening. Water vines early in the morning so leaves can dry before sunset, which helps prevent fungal disease.
Keep ripening watermelon from direct contact with soil to prevent rot and protect fruit from pests and rodents. When fruit is about the size of a softball, place it on a bed of straw or cardboard. Setting fruit on a light-reflecting surface, such as aluminum foil, will concentrate heat and speed up ripening. If large critters, such as groundhogs, discover your melons, protect ripening fruits by covering them with laundry baskets weighted down with a few bricks.
Some gardeners like to switch fertilizer during the course of the growing season. During the time from transplanting to when the first flowers open, use a fertilizer with more nitrogen than phosphorus and potassium. Once flowering begins, use a fertilizer with less nitrogen and more phosphorus and potassium, such as African violet food or liquid seaweed.
A garden adage suggests pinching off a vine’s growing shoots as watermelons start to ripen to cause the plant to divert all its energies to fruit ripening. Recent research has proven this to be false. It’s a vine’s leaves that produce the sugars that sweeten fruit. Anything that reduces the total number of leaves available for sugar production reduces watermelon sweetness.
In colder regions, remove any blossoms that start to develop within 50 days of your area’s first average frost date. This ensures remaining, larger fruits will ripen before frost.
Watermelons are in the same plant family as squash and cucumbers, but they do not cross-pollinate successfully. Your garden will depend on bees to pollinate the flowers, so cool cloudy weather in the spring will slow down thier development. Be patient until the weather warms.Fungal diseases can multiple rapidly on melon leaves. Alternaria leaf spot, anthracnose, and gummy stem blight produce spots on leaves, while stem blight also forms bleached or tan sections on stems and rot on fruit. Downy mildew causes yellow or pale green leaf spots, while powdery mildew produces white spots on leaves. Treat fungal diseases with fungicides. Check with your local garden center or Extension service to learn which fungicides are approved in your state for the disease you’re fighting.
Melon aphids can quickly colonize a vine, so inspect leaf undersides daily. If you spot aphids, treat them with insecticidal soap.
Spotted and striped cucumber beetles can attack vines, transmitting bacterial wilt disease, which causes vines to collapse. Infected vines don’t recover. Treat adult beetles with rotenone or a pyrethrum-based insecticide; apply at dusk to avoid harming honey bees.
Watermelons typically ripen over 2 weeks. As soon as one melon is ripe, the others won’t be far behind. About a week before a melon is ripe, water only as necessary to keep vines from wilting. Withholding water causes sugars to concentrate in the fruit. Too much water reduces sweetness.You can judge a watermelon’s ripeness by its skin color. The rind changes from a bright to a dull green, and the part that touches the soil shifts from greenish white or straw yellow to rich, creamy yellow. Gardeners also judge a watermelon’s ripeness by rapping on the skin and listening for a low-pitched thud. Tune your ear to the incorrect sound by rapping on a few fruits that aren’t ripe. Underripe fruits resonate with a high-pitched, tinny sound.
Watermelons will keep 2 to 3 weeks unrefrigerated. Place them in a cool basement to increase their holding time. After cutting, refrigerate unused portions. If you have extra melon on hand, dice or cut the flesh into balls and freeze for slushies.
How do you know when a watermelon is ready to be picked?
Will a watermelon turn sweeter the longer you wait after harvest to eat it?
How do you know if a watermelon is going to be sweet?
How do you store watermelons?