Adams County Master Gardener
One of the joys of my summer garden is growing and eating watermelons. My love of watermelons comes from spending summers on my grandfather’s farm where he raised them for us to enjoy. Nothing was better than sitting under the farm’s huge
trees eating cool watermelon dripping with sweet juices. I have grown watermelons for the last several years with great success, harvesting over 500 lbs. from three hills the last two years when, just for fun, I started weighing each watermelon.
Watermelons originated in Africa and were first cultivated in Egypt and India. There are over 500 varieties. Watermelons come in three main seed groups: early season, main season and seedless. Early season watermelons mature in 70-75 days and produce the smaller sized fruit, often called "ice box" melons since they readily fit on a refrigerator
shelf. Some are even yellow skinned with red fruit such as the Japanese varieties Golden Crown and Yellow Jubilee.
Main season melons produce in 80-85 days, weigh 18-30 pounds and usually have dark green rinds. The type I like to grow is Sangria. It gets really large; my biggest so far weighed 36 pounds. Their taste is very sweet and crisp, readily overcoming the fact that they contain seeds. Seeded main season watermelons also come in yellow or orange-fleshed
varieties such as Desert King or Tendergold.
Understanding genetics is the key to growing seedless watermelons. Seedless watermelons are sterile hybrids that produce no fully developed seeds in the fruit. Some immature edible white seeds may form. Production of seeds to grow seedless watermelons is extremely labor-intensive so one
only finds seedless plants in nurseries. Normal seeded melons are "diploid" meaning they have two sets of chromosomes, one set from each parent. To obtain a seedless melon seed, a seeded parent is treated with colchicine (derived from autumn crocus and used to treat gout) causing four sets of chromosomes to be developed. The resulting "tetraploid" plant is crossed with a
regular "diploid" plant to create a "triploid" plant containing three sets of chromosomes.
"Triploid" plants produce seedless watermelons. Because of the odd number of chromosomes, they are unable to form seeds in the fruit. However, these plants still produce female flowers, but they cannot make viable pollen for fertilization needed to grow fruit. As a result, a seeded watermelon must be grown along with a seedless variety to provide
pollen for fertilization and fruit formation. Keep that in mind if you want to grow seedless watermelons in your home garden. You must grow at least one seeded watermelon plant in order to grow any seedless watermelons.
Watermelons require full sun, plenty of nutrients, water, and room to vine during the growing season. Transplant seedlings well after the frost date when the soil has warmed to 60+ degrees. I use a gallon milk jug with the bottom cut out or circular water-tube protectors to give my plants a head start by creating a mini-greenhouse. It keeps the
seedlings warm during early spring. My secret weapon is liberal use of composted mushroom soil to improve the soil and mulch the plants in addition to planting flowers near the watermelon plants to attract pollinators.
Watermelons can result only from successful pollination. Male flowers appear first on the main vine runners while female flowers appear later on lateral shoots. A female flower will have a tiny marble-sized watermelon below the flower. Once main vines reach about 10 feet, if no female flowers have appeared, nipping the main vine ends can force side
shoot formation leading to female flower production. Female flowers also can be hand pollinated by dabbing the female flower with a male flower or using a paintbrush. Flowers open early in the morning and last usually only one day.
Judging when to pick a ripe watermelon is not a simple task. I usually end up sacrificing one or two until I get it right – crisp ripe flesh without being grainy or mushy. The first tipoff to ripeness occurs when the tendril attaching the watermelon to the stem starts to dry and turns brown, and the second is when the ground spot, where the melon
rests upon the ground, begins turning from a pale green or white to a creamy yellow color. To insure the accuracy of this indicator, do not rotate your watermelons while still on the vine. Thumping is less successful for me. Supposedly a ripe melon has a muffled, dull tone while a less ripe one has a clear ringing tone. If you want to have some fun, put a broom straw on a
melon and watch it spin. I have been unable to find an accurate scientific explanation as to why this occurs, other than a comparison to dowsing for water using a forked stick.
Growing your own watermelons is a lot of fun. Give it a try. You will enjoy the fruits of your labor.
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