Summer officially began this week, which means melon season for many. According to the United States Department of Agriculture, approximately 21.1 pounds of melon were available per U.S. consumer in 2022. Among the melons that consumers acquired and enjoyed, the three most popular, in order of availability, were watermelon (14.1 pounds), muskmelon (5.3 pounds), and honeydew (1.6 pounds).
Although not all common names are accurate, like watermelon, this eponymous fruit is 92 percent water. The high water content of watermelon (Citrullus lanatus) fruit was first recognized by ancient African people, who ate it as a means of staying hydrated while living in arid environments. Evidence suggests that a relative of the modern watermelon has been enjoyed by indigenous peoples of the Kalahari Desert region for over 5,000 years, although the exact genetics and shape of the fruit are unknown.
Watermelon was imported to Egypt over time. The Ancient Egyptians are said to have refined the fruit. It is believed that wild plants had bitter flesh and a less pleasant taste than today's sweeter varieties. Seed selection changed the fruit, with sweeter fruit seeds being planted and more bitter tasting seeds being discarded. Representations found in tombs suggest that the shape of the fruit was elongated from the globular shape of the wild variety to the oval shape of the watermelon we are familiar with.
Slowly, watermelon spread across the world. We know this, and can trace the fruit's general spread, as it is mentioned in various religious, medical, and literary sources. It followed a rough migration route from the Mediterranean region to Spain, Europe, and the Americas. Through distribution and over time, cultivation continued to produce new varieties, flavors, and shapes of watermelon.
When we think of watermelon, we think of the little black seeds that are perfect for seed-spitting contests, but recent advances in genetic engineering have led to seedless watermelons. Watermelons are diploid plants, meaning that when pollinated, a pair of genes splits to produce viable offspring.
In the late 1930s, Japanese plant breeder Professor Hideichi Kihara succeeded in producing watermelons with double the genes (tetraploids). Seedless watermelons are produced by crossing a diploid (two times) parent with a tetraploid (four times) parent to produce triploid (three times) offspring. Because the offspring have an odd number of chromosomes, they cannot divide evenly during growth and cannot produce viable offspring (seeds).
Although seedless watermelon is popular with consumers, this hybridization creates several production problems. Because no viable seeds are produced, obtaining seedless watermelon requires growing extra plants that do not produce marketable fruit and investing more resources into these plants that do not result in a return on investment. Other options being considered by commercial growers include hand pollination where labor costs are low, and pollination by honeybees in isolation blocks.
Despite production challenges, about 90 percent of watermelon cultivars grown for consumption in the United States are seedless.
Watermelons belong to the Cucurbitaceae family, the same family as cantaloupes, honeydews, cucumbers, and pumpkins. Plant seeds after danger of frost has passed and the soil has warmed. Watermelons prefer well-drained, sandy loam soil, which keeps moisture off the developing fruit and minimizes problems with disease and rot. Because the roots grow relatively deep, the plants only need to be watered during extended dry periods.
The plants are vine-like plants, so they need lots of space: space the rows about 6 feet apart, with 7 feet between rows.
Cucurbitaceae plants are dioecious, with separate male and female flowers on the same plant. If you have limited space to grow watermelons, it's good to know that watermelons are self-fertile, meaning that male flowers can pollinate female flowers on the same plant to produce fruit. Watermelon pollen grains are large, heavy, and sticky, so they require the help of insects to move. Without sufficient pollination, the fruit will wither and become misshapen.
New cultivars producing yellow or orange flesh are available for professional growers and enjoyment in the home garden. Growing conditions and techniques are the same as for the traditional red-fruited varieties.
Emily Swihart is a horticulture educator with the University of Illinois Extension serving Henry, Mercer, Rock Island and Stark counties. This column also appears on the “Good Growing” blog at go.illinois.edu/goodgrowing.
