Growing Watermelon in the Home Garden

Growing watermelon in a home garden allows you to enjoy this refreshing, sweet fruit from your backyard. Watermelons thrive in warm, sunny conditions and require ample space to spread out. While they are relatively easy to grow, successful cultivation involves understanding their specific needs, including soil requirements, watering, and pest management. Learn tips and techniques for growing watermelon, from selecting the right variety to harvesting the perfect melon, ensuring a bountiful harvest at home.

Watermelon (Citrullus lanatus) is a member of the Cucurbitaceae family and is closely related to other family members including cantaloupe, pumpkins, squash, gourds, and cucumbers. A native of tropical Africa, it has become a staple summer treat worldwide. Plants are vining and are typically allowed to ramble along the ground. They can, however, be trained to trellises, although support must be given to the large developing fruit as it enlarges and ripens.

Pollination of Watermelon

Watermelons are monoecious—meaning they produce separate male and female flowers on the same plant. The female flowers develop into fruit after bees transfer pollen from the male flowers. You can identify female flowers because they have a small melon-shaped bump at the base of the flower.

Each female flower is open and receptive to pollination for only one day. The more bee visits per flower, the greater the number of seeds per fruit, the larger the size of the fruit, and the fewer number of misshapen fruit. Cool, rainy, or windy weather limits bee activity and pollination. Low temperatures can prevent the development and release of pollen.

Avoid using insecticides that are injurious to bees. When insecticides are needed, apply early in the morning or late in the evening when bees are less active.

Planting

Site Requirements

Plant watermelons in full sun and fertile, well-drained soil with a soil pH of 5.5-7.0. The planting site should receive at least 6 hours of direct sun each day. Heavy, poorly drained soils can often be improved by incorporating organic matter, such as compost or well-rotted manure, into the soil.

When to Plant

Watermelons are warm-season crops. Plant melons after the danger of frost is past and soil temperatures have warmed to 60 to 70°F. Watermelons can be planted in mid-May in central Iowa. Gardeners in southern Iowa can plant about one week earlier—plant one week later in northern areas of the state. The last practical date to sow early maturing watermelon varieties is June 20.

Watermelon takes a relatively long time to grow to maturity. Getting an early start is desirable, but early planting is not possible when spring temperatures are too cold. For an earlier crop, melon transplants can be started indoors. Start seeds indoors 3 to 4 weeks before the anticipated outdoor planting date. Plantable containers, such as peat pots, work best as both plant and container are transplanted directly into the garden, resulting in little damage to the transplant's root system. Sow 3 or 4 seeds per container. Later, remove all but two seedlings. Transplant outdoors when plants have 1 or 2 true leaves. Harden the plants outdoors for a few days prior to planting to lessen transplant stress. Initially, place the transplants in a shady, protected location and then gradually expose them to longer periods of direct sun.

How to Plant

Watermelon is usually planted in hills. Plant 4 or 5 seeds per hill at a depth of 1 inch. Later, remove all but 2 or 3 healthy, well-spaced plants per hill when seedlings have 1 or 2 true leaves.

Watermelon hills should be spaced 2 to 3 feet apart in rows 6 to 8 feet apart. If garden space is limited, bush-type varieties are available.

Care

Fertilizer

Apply 1 to 2 pounds of 10-10-10 or a similar analysis fertilizer per 100 square feet of garden area prior to planting. Use the lower rate on sandy loam soils and the higher rate on heavier, clay-based soils. For specific recommendations, conduct a soil test.

When setting out transplants, apply a starter fertilizer solution at the rate of 1 pint (2 cups) per transplant. For the starter solution, follow the label directions on a water-soluble fertilizer or dissolve two tablespoons of all-purpose garden fertilizer, such as 10-10-10, in one gallon of water.

Watering

While watermelons will not tolerate wet conditions, they require consistent and abundant moisture. Plants should not be allowed to dry out. Dry conditions during germination result in poor and uneven seed emergence. A shortage of moisture at bloom results in poor fruit set and misshapen fruit. Moisture stress close to harvest greatly reduces melon size and results in rapid vine decline. Therefore, a consistent supply of soil moisture should be maintained from germination through harvest.

Drip irrigation works well as it provides water directly to the root zone and reduces the wetting of the foliage which can promote disease issues and weed growth (both of which are difficult to deal with when growing watermelons).

During dry weather, irrigate by applying 1 to 2 inches of water every 7 to 10 days. Irrigate in the early morning to reduce foliage diseases. As the fruit approaches maturity, apply half as much water per application.

Soil type does not affect the amount of total water needed, but it does affect the watering frequency. Sandy soils need to be watered more frequently but require less water per application.

Weed Control

Controlling weeds can be difficult as the foliage canopy does not provide dense cover to shade out germinating weed seedlings fully. Additionally, it can be difficult to walk among the vines to pull or hoe weeds without damaging stems or fruit. Utilize mulch, like grass clippings, straw, cocoa hulls, or plastic, to conserve moisture and reduce weed growth. Pull or hoe weeds carefully to not damage the shallow root system. Stay ahead of weeds, removing them before they become large or difficult to access.

Using Black Plastic

Black, clear, or colored plastic mulch film can be used to promote early melon production. Plastic promotes spring growth by allowing sunlight to more efficiently warm the soil. The plastic mulch also helps to conserve soil moisture and control weeds.
Lay the plastic over moist soil on a calm day. If the plastic is laid over dry soil, it will delay subsequent plant growth. Anchor the edges of the plastic mulch by making furrows 2 or 3 inches deep.
Place the edges of the plastic in the furrows, then fill the furrows with soil. To plant, simply cut holes in the plastic with a sharp knife or bulb planter. The holes should be in the center of the plastic film and just large enough to plant the seeds or transplants.

When using plastic mulch, use the lower rate of fertilizer. Incorporate the fertilizer into the soil before laying down the plastic. Regular irrigation is required as the plastic does not allow for water to penetrate. The best option is to use drip irrigation under the plastic mulch. It helps to produce higher yields and discourages foliar diseases.

Harvest & Storage

Harvest when the underside or "belly" of the melon turns from a greenish white to buttery yellow or cream. This color change is especially pronounced on the dark green-skinned varieties. It is often less noticeable on lighter-skinned watermelons. In addition, the fruit tends to lose its slick appearance on top and becomes dull when ripe.

The browning of the pig's tail (light green, curly tendril attached to the vine near the melon) is another option for determining ripeness. In some varieties, the pig's tail may turn brown 7 to 10 days before the melon is ripe making this method of determining ripeness unreliable in some varieties. Often, the browning of the pigtail can be used in conjunction with the change in belly color to determine ripeness, especially for those varieties whose belly color change is not easily seen.

Thumping or tapping the melon is generally not a good indicator of ripeness. Rapping an immature melon with your knuckles produces a metallic ring. A ripe melon gives off a hollow or dull ring. Most individuals, however, have difficulty differentiating between the sounds.

Expected yield for watermelon tends to be about 2 to 3 melons per plant. When harvesting watermelons, leave 2 inches of the stem on the fruit. Watermelons can be stored at room temperature for about one week and two to three weeks at 50 to 60°F.

Potential Problems

Poor Fruit Set, Blossom Drop, Fruit Drop

Poor fruiting of vine crops may be due to the plant's flowering habit and poor pollination. Learn more about poor fruit set in this article: Reasons for Poor Fruiting of Vine Crops.

Blossom-End Rot

Blossom-end rot is a physiological disorder most familiar to gardeners growing tomatoes, but it can happen on other vegetables, including peppers, eggplants, cucumbers, squash, and melons. On watermelon, the blossom end of the fruit begins to rot, and within a short time, the entire fruit has rotted. Blossom-end rot is caused by a lack of calcium in the developing fruit. In most cases, there is no need to apply calcium to the soil. Try to maintain an even moisture supply by watering once a week during dry weather. Also, do not over-fertilize plants. Uneven moisture supplies and excessive nitrogen inhibit calcium uptake.

Poorly flavored and Colored Fruit

Poorly drained soils, heavy rainfall, or too much irrigation for a week or two before harvest can cause poor flavor and lower sugar content.
Excessive moisture and too much nitrogen during fruit ripening may cause white heart of watermelons.

Fruit Cracking or Bursting

Heavy rainfall or too much irrigation, especially as the watermelon approaches maturity in the week or two before harvest, can cause bursting and cracking of the fruit.

Damping-Off

Pythium damping-off attacks the roots and stems of germinating seeds and young seedlings. Stems turn brownish and water-soaked at their bases and may fall over and wither. Leaves of some transplants may turn yellow, while others dry up and die within a few days after planting.

Cool, wet conditions make transplants and newly germinated plants vulnerable to Pythium damping-off.

Most commercial melon seeds are treated with fungicides to deter damping-off. However, damping off can still occur when environmental conditions are particularly favorable. It is often best to avoid planting when conditions are too cool and wet. It is better to plant a little later when conditions warm and/or dry out than to risk losing plants to damping off.

Should seedlings die, replanting is often possible and can be done immediately following the removal of dead seedlings as long as weather conditions are favorable.

Fungal Diseases

Some foliar diseases appear where air circulation is reduced and leaves remain wet, such as in low areas and along borders sheltered by trees. Foliar diseases typically appear first on leaves close to the base of the main stem. Common foliar diseases on watermelon include powdery mildew (Podosphaera xanthii, Podosphaera fuliginea), Downy mildew (Pseudoperonospora cubensis), Cercospora leaf spot (Cercospora citrullina), Alternaria leaf blight (Alternaria cucumerina), and Angular leaf spot (Pseudomonas syringae), among others.

Gummy stem blight (Didymella bryoniae) occurs more frequently when temperatures are warm and humid. Brown or white lesions form on stems and crowns and occasionally ooze and amber-colored sticky substances.

Wilt diseases like Fusarium wilt (Fusarium oxysporum) and Verticillium wilt (Verticillium dahliae) can cause wilting confined to one or more vines. As it progresses, more leaves wilt for longer periods, and leaves turn yellow. Stems may also develop discolored vascular tissue.

In the home garden, fungal diseases are best controlled through preventative measures. Avoid overhead watering or water in the morning so foliage can dry quickly during the day. Avoid working in wet foliage (from irrigation or heavy dew) to prevent the spreading of fungal diseases. Reduce soil splash by putting down a layer of mulch to lower the potential of spreading fungal diseases from soil to plants. Remove and destroy dead foliage at the end of the growing season. Reduce weeds and eliminate possible alternate hosts for common diseases. Crop rotation is also very beneficial. Make sure not to plant watermelon or any other cucurbit (squash, cucumber, melon, etc.) in the same area for at least 3 to 4 years. Frequent scouting to identify and respond to disease issues as soon as they are observed is important. To control diseases, fungicides (if used) are most effective when applied at the onset of visible disease symptoms. Fungicides are not as effective on wilt diseases as the organism is inside the stem tissue, making it difficult to get fungicides to them.

Viral Diseases

Viral diseases often cause stunted and/or distorted growth and fruits. Leaves may become mottled or develop interveinal chlorosis, leaving a mottled appearance. Viral diseases that affect watermelon include Watermelon mosaic virus (WMV), Cucumber mosaic virus (CMV), Cucumber green mottle mosaic virus (CGMMV), and Zucchini yellow mosaic virus (ZYMV).

These viruses can be transmitted by seed, so buying certified virus-free seed is beneficial. Insect vectors, such as aphids, can also spread them. Reducing aphid populations can reduce the spread of the disease to other plants. Clean and disinfect tools regularly, as tools and hands also transfer viral diseases. Select varieties that are resistant to viral diseases. Remove and destroy any virus-infected plants and all those plants in the immediate area (3 to 5 feet radius). Rotate crops to prevent future spread.

Fruit Blotch

A bacterial disease called watermelon fruit blotch occasionally occurs in Iowa. Symptoms often appear at midseason as water-soaked or coffee-colored stains on fruit. The stains develop cracks, and secondary microorganisms can invade and rot the fruit. In some cases, infected fruit split open. The disease can be brought into a garden on infected seeds or transplants. Infected seedlings can have watersoaked areas on the foliage and abundant bacterial streaming under the microscope.

Once observed, there is not treatment that will eliminate the bacterial disease. For future plantings, use pathogen-free seeds and transplants. Practice good crop rotation and avoid overhead watering.

Insect Pests

Insect pests are usually most critical in the seedling or early growth stage. Row covers applied at planting and removed at first bloom (so pollinators can do their work) can be used to exclude insect pests. Cucumber beetles, squash bugs, mites, and aphids are the most common insect pests of watermelons.

Control can be done in home gardens using cultural techniques like hand-picking, row covers, good weed management, and trap crops. Organic and synthetic insecticide applications are more effective when made early in the season when insect pests are small and easier to kill. Insecticide applications should be made only when necessary, as determined by field observations and correct insect pest identification. Insect populations often fluctuate greatly from year to year.

Recommended Cultivars

Cultivars that do well in Iowa include,

Seeded, Large

'Black Tail Mountain' (red-fleshed, round, 8-12 lbs.)
‘Crimson Sweet’ (red-fleshed, blocky round fruit, 20 to 30 lb.)
‘Royal Sweet’ (red-fleshed, blocky oval fruit, 20 to 25 lb.)
‘Sangria’ (red-fleshed, blocky oval fruit, 20 to 26 lb.)
'Yellow Baby' (yellow-fleshed, 9 - 12 pounds)

Seeded, Small

'Cathay Belle' (red-fleshed, round, 7-10 lbs)
'Jade Star' (red-fleshed, 10 - 12 lb.)
'New Orchid' (orange-fleshed, round, 7-9 lb.)
'Starlight' (red-fleshed, round, 10-12 lb.)
'Sugar Baby' (red-fleshed, solid dark rind, round, 8-10 lb.)
'Sureness' (yellow-fleshed, round, 8-10 lbs.)
‘Sweet Beauty’ (red-fleshed, oblong, 5 to 7 lb.)
'Yellow Doll' (yellow-fleshed, round, 5-7 lbs.)

Seedless, Large*

‘Amarillo’ (yellow-fleshed, round fruit, 12 to 14 lb.)
'Cooperstown' (red-fleshed, 16 - 22 pounds)
‘Crunchy Red’ (red-fleshed, round to oval fruit, 15 to 18 lb.)
‘Gypsy’ (red-fleshed, round fruit, 13 to 17 lb.)
‘Millionaire’ (red-fleshed, oblong fruit, 13 to 20 lb.)
'Orange Crisp' (orange-fleshed, round, 17-19 lb.)
'Sweet Gem' (red fleshed, round, 13-16 lb.)

*A seeded variety (pollenizer) must be planted with seedless watermelon varieties for proper pollination. Pollinator seeds are often included in seedless watermelon seed packets. Plant a pollenizer with a different rind pattern than your crop so you can differentiate the seedless fruit from seeded pollenizer. Fruits from pollenizer plants are also edible.

More Information

Authors:

Aaron Steil

Last reviewed:

July 2024