watermelon

Watermelon is, as the name suggests, mostly water.

Humans have cultivated watermelon for more than 5,000 years.

Tombs of Egyptian royalty often contained watermelons, and hieroglyphics depicted watermelon harvests. Watermelon is believed to have originated on the African continent, although many countries claim long histories with the fruit.

Watermelon flesh is mostly water, has little nutrition and few calories. On the other hand, watermelon seeds have 600 calories per cup and are a powerhouse of nutrients. The seeds can be roasted and used much like sunflower seeds. In times of food scarcity, watermelon seeds are more important than the flesh.

The white part of the rind can be used as a crunchy vegetable, or pickled. Many animals are also fond of watermelon. No wonder watermelons are grown widely all around the world.

Nothing says summer like a sweet, juicy, ripe watermelon. They are highly coveted by home gardeners and easy to grow. Watermelons require ideal conditions, otherwise yields are low or plants will die. They require consistent heat, full sun, evenly moist, fertile soil, and bees.

Watermelon is very picky about the temperature, needing a long, sustained growing season where the nighttime temperatures remain above 70 degrees, and warmer is better. Temperatures lower than 60 degrees can kill the plants. With vines that grow 20 feet or longer, watermelons need a lot of garden space.

The vines have male and female blooms that need multiple visits by insects to achieve pollination; planting blooming flowers among the vines will increase the number of visits by pollinators. (Buckwheat and agricultural mustard are both very attractive to pollinators.)

Frustrated gardeners lament that the first blooms are mostly male — so no fruit sets. When female flowers finally do appear, only about 15% will actually set fruit. It’s good to plant extra.

Watermelon can be started from seed about three to four weeks before transplanting into the garden. Seedlings must be handled with care as they don’t like the transplanting process. Those seedlings will not survive cool nights or cold soil. Use a soil thermometer for about a week to confirm that the soil temperature is consistently above 70 degrees; if not, wait another week or two. After the soil is warm it can be covered in 2 inches of straw or shredded leaves to help retain soil moisture.

It is helpful to plant short-season varieties like Sugar Baby and Blacktail Mountain that are ready to harvest in about 80 days. In Yakima, varieties that take longer than 100 growing days may not have enough time to reach maturity.

There are many ways to tell if a watermelon is ready for harvest. Some people look for a yellow spot on the underbelly. Some tap on the underbelly of the fruit; if it sounds hollow it’s supposed to be ready. Others say the shiny green color should develop a dull powdery sheen.

These are a bit subjective and require more art than science. It’s easier and more reliable to look at the first tendril closest to the stem; when it’s completely brown and brittle the watermelon is ripe.

How long a melon lasts in storage depends on the variety. Most watermelons will not continue to ripen after harvest. Usually uncut watermelons will last two weeks in a cool storage area. Once cut, expect three to five days in the refrigerator. Some varieties are long-keepers and are not sweet. They are often eaten as pickles and in cooked dishes. However, Blacktail Mountain is a sweet, red fleshed, short season, long keeper. Plant breeders claim it will last two to three months when stored in a cool, dry, dark place.

Home gardeners demand varieties with good flavor, and that usually means seeded varieties. Yet, 92% of commercially grown watermelons in the U.S. are seedless. Seeds for seedless watermelon varieties are not always available in local stores and nurseries, but are fairly easy to find online.

Each year, the Master Gardeners clinic receives the question, “If the watermelon has no seeds, where did the seeds in the packet come from?” It’s a complicated answer based on chromosomes, manipulating them and cross-pollination over several generations. The process was invented by Professor H. Kirata in Japan in 1939.

Seedless watermelons are not considered to be genetically modified or genetically engineered, even though they are not naturally occurring. Watermelons normally have 22 chromosomes. By treating seeds with colchicine, an organic powder made from the corms of saffron meadow crocus, and then planting the treated seeds, the new melons will have seeds with 44 chromosomes. Then you have to grow watermelons with 22 chromosomes and cross-pollinate with watermelons with 44 chromosomes. The resulting seeds will have 66 chromosomes but organized in 22 sets of three rather than pairs of chromosomes, and voilà! Seedless watermelons.

This is a very simplified explanation of the process. All you really need to remember is that it takes several growing seasons and cross-pollinations before you actually get seedless watermelons. Next time you eat one, take a moment to appreciate the effort involved to get the seeds out of the watermelons that we so love to eat. It’s pretty amazing!

The WSU Extension office that houses the Master Gardener clinic is closed because of the coronavirus pandemic. However, we will continue to answer your gardening questions; call 509-574-1604 and leave a detailed message. We also will respond to emails at www.gardener@co.yakima,wa.us. Again, leave a detailed message and include your contact information so we can call if we have questions. If you have photos as evidence of a problem, attach them as well; we are not accepting any physical samples at this time.