Jennifer Schultz Nelson
Extension Educator, Horticulture
In my opinion, one of the greatest things on a blazing hot summer day is a cool slice of watermelon. A favorite family picture of mine is of me and my grandpa–I'm about five years old, and we're both eating watermelon. Young and old, we're sitting in exactly the same position, intently focused on the big watermelon slices in our hands.
As a kid, I remember an added bonus of eating watermelon in the summer was that it was the only time it was ok to spit! Of course, I also remember older relatives scaring me with stories of watermelon vines growing in my belly if I swallowed a seed instead of spitting it out. That could never happen, but in my young mind I pictured yards of watermelon vines tangled in my stomach!
We enjoy cool juicy watermelon as a treat today, but so did people thousands of years ago. Illustrations from ancient Egypt show watermelons being harvested for food, and historians believe they were one of the food items placed in ancient Egyptian tombs to nourish the recently deceased person in the afterlife.
Watermelon, Citrullus lanatus, is believed to have originated in southern Africa, in the Kalahari Desert. Explorers have identified what appears to be the 'wild' watermelon, referred to as the Tsamma melon by locals, identified as Citrullus lanatus var. citroides by scientists.
A single vine can produce up to 100 melons, and its flesh is similar in consistency to the rind of modern watermelon. The flesh has a naturally high pectin content, making it a useful ingredient in jams and jellies.
This wild ancestor of the watermelon also has a very important and practical use that dates back centuries. It is a valuable source of water. Some native people grow this ancestor of watermelon specifically as a water source.
European explorers and colonists are credited with bringing the watermelon to North America as early as the 1500s. African slaves have also been credited with bringing the watermelon to the New World, particularly the area that is now the southern U.S.
There is an enormous range of sizes and shapes of watermelon, as well as different flesh and seed colors. We typically think of watermelon as being red-fleshed, but shades of yellow and even white exist. The seeds are typically black, but can be brown, white, and even red.
The National Watermelon Promotion Board (www.watermelon.org) says there are anywhere from 200 to 300 varieties of watermelon grown in the U.S. and Mexico, but only about 50 that would qualify as 'popular' with consumers.
It may surprise you that up until the 1940's, it was difficult to find a good watermelon at the grocery store. The available varieties just did not store or ship well. A breakthrough in commercial watermelon production came when Charles Fredric Andrus, a USDA plant breeder at the Vegetable Breeding Laboratory in Charleston, South Carolina began selecting watermelon to develop a disease-resistant cultivar. The result was the watermelon now known as 'Charleston Gray'. This large, oblong, gray-green melon was not only resistant to the most serious watermelon diseases, it also had a very thick rind which made it easy to ship. Today, most commercial watermelon cultivars have 'Charleston Gray' somewhere in its pedigree.
One of the more amusing commercial watermelon innovations I've seen is the square watermelon. Farmers in Japan developed this novelty, hoping it would catch on as a way to efficiently use space in shipping and storing watermelon. To grow the square watermelons, farmers allow individual watermelons to grow inside glass boxes, and as they grow bigger, they take on the shape of the box. The problem is this requires so much extra labor that the melons often end up costing over twice that of a normally-shaped watermelon.
Watermelon is a crop that relies on bees for pollination. Watermelon is a member of the Curcurbit family, which includes cucumbers, pumpkin and squash. Like these cousins, the watermelon has separate male and female flowers. The bees are crucial for transferring pollen from male to female flower. The USDA recommends at least one beehive per acre in commercial production of seeded watermelon.
To produce seedless watermelon, bees are still needed. In growing seedless watermelon, there are actually two genetically different plants grown side-by-side–one to provide pollen, the other produces fruit but no viable pollen. The fruits these plants produce are called 'seedless' but they actually have tiny, undeveloped seeds inside that fail to develop because of the genetics of the mother plant.
Typically the only parts of the watermelon consumed in the U.S. are the flesh, and occasionally the rind as pickles. In other parts of the world, particularly Asia, the seeds are roasted and eaten, much like sunflower seeds. In Russia they've even figured out how to brew watermelon juice to make beer!
Growing watermelon in the home garden is not as hard as you may think. The biggest factor for success is space, and lots of it. Watermelon vines need room to sprawl. They also do best planted after the soil is warm, in soil that drains exceedingly well, such as sandy soil. Mulching is recommended to conserve moisture and protect developing fruits and vines from diseases that can transfer from the soil.
Depending on the cultivar, watermelon needs at least 90 days from planting to produce edible fruit. At this point, it's too late to plant watermelon and harvest any. However, this is the perfect time to stop at your local Farmer's Market or roadside stand and take home a juicy watermelon.
There are a million 'old wives' tales' on how to choose a ripe watermelon. Some work, some don't. If you are picking the watermelon yourself, look at the tendril on the vine closest to the melon. A tendril is a corkscrew-shaped bit of plant tissue that the vine uses to secure itself to its surroundings. On a ripe watermelon, the tendril closest to the melon will be dried up and brown.
Another indicator which works on already-picked melons too is to look at the spot where the melon rested on the ground. This spot turns yellow as the watermelon ripens and matures.
An unreliable method of assessing ripeness is tapping or thumping. This method works, but only in the early morning, on freshly picked melons or those still on the vine. A light metallic sound when thumped means the melon is not ripe. A dull thud signals ripeness. If you tap melons in the heat of the day or after they've been picked awhile, they all sound ripe.
Hopefully before summer's end you'll find yourself a nice ripe watermelon and enjoy a slice or two. I highly recommend doing this outdoors with friends or family and seeing who can spit the seeds the farthest!