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Watermelon

Watermelon is a tender, warm-season vegetable. Watermelons can be grown in all parts of the country, but the warmer temperatures and longer growing season of southern areas especially favor this vegetable. Gardeners in northern areas should choose early varieties and use transplants. Mulching with black plastic film also promotes earliness by warming the soil beneath the plastic. Floating row covers moderate temperatures around the young plants, providing some frost protection in unseasonable cold spells.

Seedless watermelons are self-sterile hybrids that develop normal-looking fruits but no fully developed seeds. The seeds for growing them are produced by crossing a normal diploid watermelon with one that has been changed genetically into the tetraploid state. The seeds from this cross produce plants that, when pollinated by normal plants, produce seedless melons.

In seedless watermelons (genetic triploids), rudimentary seed structures form but remain small, soft, white, tasteless and undeveloped tiny seedcoats that are eaten virtually undetected along with the flesh of the melon. Seed production for these seedless types is an extremely labor intensive process that makes the seeds relatively expensive. Because germination of these types is often less vigorous than normal types, it is recommended that they be started in peat pots or other transplantable containers, where the germinating conditions can be closely controlled Once transplanted, cultivation is similar to that for regular watermelons.

For pollination necessary to set fruit, normal seed types must be interplanted with seedless melons. The pollinator should be distinct from the seedless cultivar in color, shape or type so that the seedless and seeded melons in the patch can be separated at harvest. Because seedless types do not put energy into seed production, the flesh is often sweeter than normal types and the vines are noticeably more vigorous as the season progresses.

Recommended Varieties

Early (70 to 75 days to harvest)

Golden Crown (red flesh, green skin; skin turns yellow when ripe)

Sugar Baby (red flesh, 6 to 10 pounds)

Yellow Baby (hybrid-yellow flesh, 6 to 10 pounds)

Yellow Doll (hybrid-yellow flesh, 6 to 10 pounds)

Main Season (80 to 85 days)

Charleston Gray (red, 20 to 25 pounds)

Crimson Sweet (red, 20 to 25 pounds)

Madera (hybrid-red, 14 to 22 pounds)

Parker (hybrid-red, 22 to 25 pounds)

Sangria (hybrid-red, 22 to 26 pounds)

Sunny's Pride (hybrid-red, 20 to 22 pounds)

Sweet Favorite (hybrid-red, 20 pounds).

Seedless (all are triploid hybrids, 80 to 85 days)

Cotton Candy (red, 15 to 20 pounds)

Crimson Trio (red, 14 to 16 pounds)

Honey Heart (yellow flesh, 8 to 10 pounds)

Jack of Hearts (red, 14 to 18 pounds)

Nova (red, 15 to 17 pounds)

Queen of Hearts (red, 12 to 16 pounds)

Tiffany (red, 14 to 22 pounds).

When to Plant

Plant after the soil is warm and when all danger of frost is past. Watermelons grow best on a sandy loam soil, although yields on clay soils can be increased significantly by mulching raised planting rows with black plastic film.

Spacing & Depth

Watermelon vines require considerable space. Plant seed one inch deep in hills spaced 6 feet apart. Allow 7 to 10 feet between rows. After the seedlings are established, thin to the best three plants per hill. Plant single transplants 2 to 3 feet apart or double transplants 4 to 5 feet apart in the rows.

Start the seeds inside 3 weeks before they are to be set out in the garden. Plant 2 or 3 seeds in peat pellets, peat pots or cell packs and thin to the best one or two plants. For expensive seedless types, plant one seed to a pot or cell and discard those that do not germinate. Do not start too early - large watermelon seedlings transplant poorly. Growing transplants inside requires a warm temperature, ideally between 80 and 85°F. Place black plastic film over the row before planting. Use a starter fertilizer when transplanting. If you grow seedless melons, you must plant a standard seeded variety alongside. The seedless melon varieties do not have the fertile pollen necessary to pollinate and set the fruit.

Care

Watermelons should be kept free from weeds by shallow hoeing and cultivation. The plants have moderately deep roots and watering is seldom necessary unless the weather turns dry for a prolonged period. In cooler areas, experienced gardeners may find floating row covers, drip irrigation and black plastic mulch advantageous in producing a good crop in a short season.

Harvesting

Many home gardeners experience difficulty in determining when watermelons are ripe. Use a combination of the following indicators: (1) light green, curly tendrils on the stem near the point of attachment of the melon usually turn brown and dry; (2) the surface color of the fruit turns dull; (3) the skin becomes resistant to penetration by the thumbnail and is rough to the touch; and (4) the bottom of the melon (where it lies on the soil) turns from light green to a yellowish color. These indicators for choosing a ripe watermelon are much more reliable than "thumping" the melon with a knuckle. Many watermelons do not emit the proverbial "dull thud"when ripe. For these, the dull thud may indicate an over-ripe, mushy melon.

Common Problems

Cucumber beetles attack watermelon plants. Apply a suggested insecticide for control. If row covers are used in the early season for temperature moderation, early-season insect pests may also be excluded if the covers are applied so that the pests cannot penetrate to the crop below. These covers may be left in place until the plants start to bloom, at which time pollinating insects must be allowed to reach the flowers.

For more information on cucumber beetles, see our feature in the Bug Review.

Questions & Answers

Q. My watermelons are not very sweet or flavorful. Is the low sugar content caused by the watermelons crossing with other vine crops in the garden?

A. No. Although watermelon varieties cross with one another, cross-pollination is not apparent unless seeds are saved and planted the following year. Watermelons do not cross with muskmelons, squash, pumpkins or cucumbers. The poor quality of your melons may result from wilting vines, high rainfall, cool weather or a short growing season in extreme northern areas.

Q. What can I do to prevent my watermelons from developing poorly and rotting on the ends?

A. This condition is probably caused by an extended period of extremely dry weather when the melons were maturing. It may be aggravated by continued deep hoeing or close cultivation. Mulching the plants with black plastic film helps to reduce this problem.

Q. What causes deep holes in the tops of my watermelons?

A. The holes were probably made by pheasants or other wildlife searching for water during dry weather.

Selection & Storage

Watermelon is truly one of summertime's sweetest treats. It is fun to eat, and good for you. Watermelon seeds were brought to this country by African slaves. Today there are more than 100 different varieties of watermelons. The flesh may be red, pink, orange or yellow. There are seedless varieties and super-sweet round ones that fit nicely into the refrigerator.

Producing a good watermelon is a bit tricky in the short northern season. The sweetest watermelons grow during long hot summers. Harvesting is particularly critical because watermelons do not continue to ripen after they have been removed from the vine. They should be picked at full maturity. No amount of thumping, taping, sniffing, or shaking can actually give a clue to ripeness.

Look for melons that are very heavy and have a hard rind. Ninety percent of watermelon is water. The rind color should be right for the variety with a waxy bloom. Probably the most important indicator of ripeness is the underside which sets on the ground. Turn the melon over. It should be yellow or creamy colored on the underside. If it is white or pale green the melon is not ready to harvest.

The flesh should be deep colored with mature seeds. Most watermelons have dark brown or black seeds. The seedless variety produces a few white seeds. Once picked, uncut watermelon can be stored for about 2 weeks at room temperature especially if the temperature is about 45 to 50°. Uncut watermelons have a shorter refrigerator life, so store at room temperature until ready to chill and eat. Tightly cover cut pieces in plastic wrap and store in the refrigerator for 2 to 3 days.

Nutritional Value & Health Benefits

Watermelons are low in calories and very nutritious. Watermelon is high in lycopene, second only to tomatoes. Recent research suggests that lycopene, a powerful antioxidant, is effective in preventing some forms of cancer and cardiovascular disease. According to research conducted at the University of North Carolina at Chapel Hill, men who consumed a lycopene-rich diet were half as likely to suffer a heart attack as those who had little or no lycopene in their diets.

Watermelon is also high in Vitamin C and Vitamin A, in the form of disease fighting beta-carotene. Research also suggests that the red pigmented foods provide this protection. Lycopene and beta-carotene work in conjunction with other plant chemicals not found in vitamin/mineral supplements. Potassium is also available, which is believed to help control blood pressure and possibly prevent strokes.

Nutrition Facts (1 wedge, or 1/16 of a melon, about 1-2/3 cup)

Calories 91.52
Protein 1.77 grams
Carbohydrates 20.54 grams
Dietary Fiber 1.43 grams
Potassium 331.76 mg
Vitamin C 27.46 mg
Vitamin A 1046.76 IU

Preparation & Serving

The National Watermelon Promotion Board suggests washing whole watermelons with clean water before slicing to remove potential bacteria. The flavor of watermelon is best enjoyed raw. Heating diminishes the flavor and softens the texture. Watermelon tastes best icy cold in fruit smoothies, slushes or simply eaten from the rind.

To make melon balls, cut the watermelon in half lengthwise then into quarters. Watermelon balls can be scooped right out of rind. Create perfect balls, using a melon baller, and a twist of the wrist. The watermelon shell can be used to hold the melon balls as well as other fruit. Watermelon punch is also served from the hallow rind. By sitting the round end inside a ring or bowl, the shell will remain stable during serving.

To remove seeds, cut each quarter in half again. With the flesh of each wedge on top and the rind sitting on the counter, look for the row of seeds along the flesh of each wedge. Using a sharp knife, cut along the seed line and remove the flesh just above it. Scrape the seeds from the remaining piece.

Home Preservation

Seeded watermelon chunks can be frozen to use in watermelon slushes or fruit smoothies. Watermelon sorbet or granita stays fresh in the freezer for up to 3 months. The difference between a sorbet and a granita is in the texture. Sorbets are smooth, whereas granitas are coarse. You do not need an ice cream maker to make a granita. The best way to enjoy watermelon is while they are fresh and sweet. When they are gone, they are gone until next summer.

Recipes

Watermelon Granita

5 cups seeded watermelon pulp
1 cup sugar syrup*
2 tablespoons fresh lemon juice
Thin watermelon wedges, cut into strips for a garnish

  1. Puree watermelon in a food processor.

  2. Pour into a 9 x 13 inch baking dish. Stir in the syrup and lemon juice. Freeze for about 4 hours or until frozen solid.

  3. To serve, scrape up granita with a large spoon and place in goblets, tulip shaped wine glasses or ice cream dishes. Garnish with a narrow wedge of watermelon. Makes 4 servings.

*To make sugar syrup; Combine 1/2 cup water and 1 cup sugar in a saucepan. Bring to a boil over medium-high heat. Boil for one minute. Stirring constantly until all of the sugar has dissolved. Cool in the refrigerator.

Watermelon Smoothie

1 - 8 ounce lemon, fat-free yogurt
3 cups cubed, seeded watermelon
1 pint fresh strawberries, cleaned and hulled
1 tablespoon honey or strawberry jam
3 ice cubes

  1. In a blender or food processor, combine yogurt, watermelon, strawberries, honey and ice cubes.

  2. Process until smooth and frothy. Serve in tall glasses with a straw. Makes 4 servings.