Keith Weller, USDA/ARS
Plant Common Name
Watermelon, Wild Watermelon
Nothing celebrates summertime like a sweet slice of watermelon! A native of the southern regions of Africa, the watermelon is a tender annual vine that needs a long warm growing season to produce its famous fruits. The vines become quite large and cling using tendrils but are best left grounded. The sheer weight and size of melons precludes fence or trellis training.
Warm weather is necessary for flower and fruit development. This popular fruit produces separate male and female flowers on the same plant. The male flowers appear first followed by the fruit-producing female flowers, which have telltale bulbous protrusions at the base of their flowers. The yellow funnel-shaped blooms are bee-pollinated and appear along the stem at the base of the deeply lobed gray-green leaves.
Watermelons are highly variable in size, shape, color, flavor and sugar levels. Typically they are round or oblong and have a mottled, thick, green exterior rind and crisp, sweet, juicy, red flesh lined with many black seeds. Orange-, yellow- and white-fleshed varieties are also available, as are seedless types. The fruits can be small enough for one or big enough to feed an army platoon. Each vine typically produces two to three fruits.
Watermelons do not become sweeter after being harvested, so they must be picked when ripe. It is tricky to know when to harvest — especially considering the fruits take a while to mature and patience can wane. The best means is to monitor the tendril closest to the developing fruit. Once the tendril starts to turn brown, the fruit is ready. Another method it to keep an eye on stem health. When the stem is green and firm, the melon is still ripening; a soft withering green stem is an indication of ripeness, and a dry or unattached stem can mean over-ripeness. Finally, check the underside of the melon and give it a light knock. If the underside of the melon has turned from white to pale yellow and a hollow sound emanates from the fruit, it is probably ripe. When harvesting, cut the melon from its stem. Tearing the stem can lead to vine rot.
Full sun and fertile, well-drained, friable loam and sand are perfect for watermelon culture. They appreciate sharp drainage, so it is best plant atop low, gentle mounds of soil for the vines. After the threat of frost has passed, plant as many as three seeds in each mound and keep the soil evenly moist but not wet (wet soil can induce seed rot). Once the small plants have emerged, keep them lightly moist and feed them regularly. Provide ample room for the plants to sprawl across the ground. Plants take anywhere from 50 to 100 days to produce harvestable melons, depending on the variety and growing conditions. In regions with a cool or short summer, it is advisable to grow only early or short-season types.
There are tons of phenomenal watermelon varieties to choose from. There are heirlooms, ice box types and super sweets. The large heirloom ‘Moon and Stars’ has smooth deep green skin with prominent round yellow blotches and sweet red flesh. Another more modern variety for the table is the fantastic seedless ‘Orange Sunshine’, which has crisp, orange fruit. Finally, the tiny ‘Mini Jubilee’ has super small fruits with deep red flesh. This is just a sampling of the hundreds of cultivars.