"Watermelon is the chief of this world's luxuries, king by the grace of God over all the fruits of the earth. When one has tasted it, he knows what the angels eat." – Mark Twain
Few things are more refreshing on a hot summer day than a slice of cold watermelon. In addition to being thirst-quenching, watermelon contains vitamins, minerals, antioxidants, and other beneficial phytonutrients good for one's health. While not the richest source of nutrients from the garden, watermelon does package them in a delectable form. July is National Watermelon Month and seems like an appropriate time to explore this popular summer treat in greater detail.
Watermelon (Citrullus lanatus) is a member of the Cucurbitaceae plant family. The latter contains a number of familiar garden vegetables including cucumber, squash, pumpkin and musk melon. Members of this family are monecious, meaning they bear separate male and female flowers on the same plant. The edible part of a watermelon is known as a pepo, which is a ripened ovary (fruit) with watery flesh and a hard rind. From a usage standpoint, watermelon is consumed as a fruit, but it still is classified as a vegetable.
Aptly named, watermelon is 92 percent water and was first used by ancients as a source of water. Watermelon's history dates back 5000 years to southern Africa where the tough, drought-tolerant ancestor of watermelon thrived. Although we don't know the exact identity of this plant, we do know it was prized for its ability to store water and was used by indigenous people in the Kalahari Desert region. Unlike today's watermelon, it had very bitter flesh. Speculation exists, in addition to taking advantage of its water content, people endemic to the region roasted and ate its seeds as a source of nourishment.
Soon thereafter, watermelon found its way to Egypt where it was first improved. Both seeds and paintings of watermelon have been discovered in Egyptian tombs more than 4,000 years old. Some tomb paintings depict an oval-shaped watermelon, indicating the round wild type must have been improved by ancient plant breeders. Quite likely, it was during this period of early improvement that progress was made in developing melons with sweeter, more palatable flesh. Thus, watermelon was slowly transformed from a source of water to an enjoyable food.
From Egypt, the historical trail of watermelon must be gleaned from the likes of medical books, recipe collections, and religious codices. For example, Numbers 11:5 from the Bible references watermelon as one of the foods the Israelites longed for after leaving Egypt. Additionally, ancient manuscripts of Jewish Law record watermelon as one of the items to be tithed and set aside for distribution to priests and the poor.
The Greeks and Romans considered watermelon to have medicinal properties. Notable Greek physicians Hippocrates and Dioscorides praised its healing properties and used it as a diuretic as well as a treatment for children who suffered a heatstroke. The latter was accomplished by placing a wet, cool watermelon rind on their heads. Later, the Roman naturalist Pliny the Elder described watermelon as a cooling food in his first century publication, Historia Natualis. The latter was an encyclopedic work covering many subjects including botany and medicine.
Watermelon was being cultivated in India by the 7th century, and by the 10th century it had found its way to China. The Moors introduced watermelon into the Iberian Peninsula in the 13th century and, from there, it spread throughout southern Europe. By the 17th century watermelon was widely planted throughout Europe and had become a familiar garden crop in warmer parts of the continent.
European colonists as well as slave trade from Africa are thought to have introduced watermelon to the New World. It was found growing in Florida as early as 1576 and in Massachusetts by 1629. Thomas Jefferson grew watermelon at Monticello and, by the early part of our nation's history, it was being grown by Native American's from the Mississippi Valley south to Florida.
Watermelon improvement via selection (saving the seeds of superior melons) began almost as soon as the crop was cultivated. However, it was during the 20th century that significant progress was made in the United States where the USDA funded a watermelon breeding project at its Charleston, SC facility. One product of this research was a large, oblong light green melon that locally became known as "the grey melon from Charleston." Nearly 70 years later, 'Charleston Grey' still is a widely planted variety known for its high yields, disease resistance and table quality.
A noteworthy advance in watermelon improvement was made with the introduction of seedless watermelons in the 1950s. Seedless watermelons are the result of crossing a normal (diploid) watermelon with one that has had its chromosome number doubled to form a tetraploid strain with four sets of chromosomes. When a tetraploid (four sets) is crossed with a diploid (two sets), the result is a triploid with three sets of chromosomes. Triploids are highly sterile and very rarely form viable gametes. Thus, although produced from a seed, triploid watermelons bear no seeds. Since pollination is necessary for the enlargement of the melon, a pollinator variety must be interplanted with seedless varieties to insure melon set.
More recent improvement efforts seem to be aimed at producing smaller, "ice box" sized melons with good disease resistance and superior sweetness and taste. 'Jade Star,' 'Mambo,' 'Mini-Love,' 'Harvest Moon', and 'Cal Sweet' are just a few examples of recently introduced varieties, small-to-medium in size. Additionally, we now have yellow, orange and white-fleshed varieties for added color appeal.
Whatever the variety grown, watermelons prefer a sunny location having soil with good water-holding capacity and adequate drainage. A slightly acid soil (pH 5.8-6.5) is ideal. Watermelons grow best at temperatures between 65° and 95° F. and should not be planted until the soil has warmed in the spring. As expected, they require a constant supply of water. However, excessive moisture especially as the fruits mature can lead to melon cracking and reduced sugar content.
Weeds can limit both yield and quality and must be controlled. The use of mulch and/or herbicides can make weed control easier, since mechanical weed removal becomes difficult once the vines start to "run." Additionally, insects such as cucumber beetle, aphid, seed corn maggot, leafminers, and rindworms can all cause crop loss. Monitoring insect populations and early intervention using IPM tactics is recommended to minimize insect damage.
Troublesome watermelon diseases include bacterial fruit blotch, fusarium wilt, powdery mildew, downy mildew, and gummy stem blight. Viruses such as cucumber mosaic, squash mosaic, and watermelon mosaic also can be a problem. When possible, the use of genetically resistant varieties is the best way to combat diseases.
Watermelons are considered ready for harvest when their "belly patch" (portion of the rind that rests on the ground) turns from white to creamy yellow. Another indicator of ripeness is when the tendril located across from where the melon is attached to the vine turns from green to brown. Once harvested, watermelons can be stored at room temperature for about one week, or in refrigerated storage for two to three weeks.
As mentioned earlier, watermelons are more than just sweet and juicy, and scientists are still discovering its health benefits. Its bright red color comes from the pigment lycopene which is a powerful antioxidant. Recent studies revealed that, when combined with a healthy lifestyle, watermelon consumption can reduce the risk of both cancer and diabetes. Additionally, watermelon is a potent source of the amino acid citrulline which may help lower blood pressure. Other studies indicate watermelon consumption might be helpful in reducing the onset of rheumatoid arthritis. Finally, while most do not consider it a "diet food," a cup of watermelon contains only about 45 calories. Plus, unlike other desserts, it's fat-free, low in cholesterol, and contains no sodium.
REVISED: July 17, 2020