Watermelon

What summer picnic would be complete without watermelon?

Sweet, refreshing, and adaptable, watermelon is another easy-to-grow addition to your foodscape.

Botanically, watermelon is a type of berry called a pepo. It is also a gourd. As a member of the cucurbit family, watermelons are cousin to cucumbers, squash, pumpkins, and other melons.

Baby watermelon (Fred Hsu) CC BY-SA 3.0

History of watermelon

Watermelons were cultivated 5,000 years ago, in Ancient Egypt. Watermelon seeds were even found in King Tut’s tomb! Watermelon ancestors were not the bright red, sweet fruits we know. In fact, the original watermelons tasted pretty awful. They were bitter and hard. People grew them anyway, because these melons could hold water for weeks and even months, if stored properly. [That’s how they got their name - get it?] Five thousand years ago, that was a really Big Deal. As plumbing became a thing, watermelons had to up their game. Over time, and with selective breeding, they became the sweet summer picnic favorites that we love.

Watermelon as depicted in a 17th-century painting by Giovanni Stanchi CC BY-SA 4.0

How to grow watermelon

Watermelon plants (Citrullus lanatus var. lanatus) can take up some space. The 5-sided vines may reach 10 feet in length and the leaves are large. Plant watermelon seeds one inch deep in groups of 6 to 10 seeds. These seeds should be planted in ‘hills’ that are 3 to 4 feet apart. These hills are mounds of loose, rich soil two feet in diameter. Once seedlings emerge, save the best 3 and snip the others off at ground level. Mulch around the plants to reduce weeds and retain moisture. Individual watermelons can be grown in a container, but it should be large - at least 5 gallons. They can also be grown up trellising or on stock panels, but each melon will need a hammock.

It is best to plant watermelon in late spring, though seeds can be started two weeks after the last frost date. Seeds will not germinate at temperatures below 70°F. Row covers can be used over seedlings to protect them from pests and to retain some heat. Watermelons prefer a soil pH of 6.0 to 6.8. Watermelons do require a significant amount of water to produce fruit, but avoid getting the leaves wet to prevent fungal disease. If the leaves wilt in the afternoon, don’t worry about it. If they stay wilted into the evening, check moisture levels. Once fruit starts to appear, you will want to get it up off the ground with some straw. This reduces the chance of belly rot. Reduce watering just before your watermelons ripen to increase sugar levels and intensify the flavor.

Watermelon pests and diseases

Like most plants in hot, sunny regions, watermelon are likely to be attacked by aphids, cutworms, crickets and grasshoppers, armyworms, cabbage loopers, leaf-footed bugs, earwigs, flea beetles, leafhoppers, leafminers, nematodes, slugs and snails, thrips, whiteflies, and spider mites. As a cucurbit, watermelon is also subject to stinkbugs, cucumber beetles, and squash bugs. Many of these pests can be thwarted by dusting your melons with kaolin clay, a non-toxic fine powder that clogs up their breathing holes.

Diseases that can affect watermelon include damping off, powdery mildew, downy mildews, verticillium wilt, root rot, fusarium wilt, angular leafspot, curly top, and white mold. Nearly all of these diseases are related to overhead watering, so don’t do it. Most watermelon varieties are resistant to anthracnose, but seedless watermelons are not. Unlike other cucurbits, watermelon is not susceptible to cucumber mosaic and I have no idea why. Unsuitable environmental conditions can lead to blossom end rot, bitter fruit, blossom drop, and poor pollination.

One nice thing about growing watermelon is that you can plant the seeds in a raised bed, straw bale, or container, and then let the vine cover unplanted areas, or areas that are looking poorly. The large leaves shade the ground, stabilizing temperatures and making the soil more habitable for worms and beneficial soil microorganisms. Add a little mulch and you can be preparing that area for planting next season. Add a watermelon plant to your foodscape every summer and save the seeds for next year's crop!

Seedless watermelon (Scott Ehardt, Public Domain)

​What’s up with seedless watermelons?

Seedless watermelon production began in the 1990s. Seedless watermelons happen because plant breeders do two things:

1. They take the normal 22 watermelon chromosomes and double them, using a chemical process.
2. They pollinate female flowers of plants with 44 chromosomes with male plants that have 22 chromosome.

The resulting offspring have 33 chromosome and are highly unlikely to have viable seeds.

​Now you know.