Scientists Share Their Secrets for Choosing the Perfect Watermelon

 

Try lifting a watermelon to see if it feels heavy for its size.

Amanda Kooser

Watermelon is America’s unofficial summer fruit. Seeded or seedless, red or yellow. You can find it at the grocery store, farmers market, or, if you’re lucky, in your backyard. But every watermelon is a mystery. What’s hiding under that striped green husk? Is it sweet and ripe? Or is it tasteless and mealy? Two watermelon scientists share their secrets for choosing the perfect fruit.

Choosing a watermelon can feel like an elaborate guessing game. Weigh. Tap. Inspect. Hope. You won’t get an answer until you pay for it and take the fruit home. Here are some science-backed tips for finding a watermelon that won’t disappoint.

Horticultural scientist Penelope Perkins-Veazie studies watermelons.

Penelope Perkins-Veazie

Penelope Perkins-Veazie is a horticultural scientist at North Carolina State University. She has studied the health benefits of watermelons and even experimented with a watermelon-based sunscreen as an alternative to synthetic sunscreens.

Perkins-Veazie uses different methods depending on whether you’re picking in the field or trying your luck at the store. In the field (and this can apply to home gardeners, too), start with the tendrils and leaves. “The top three tendrils closest to the watermelon fruit should be dead,” she says. “Other subtle indicators of ripeness are changes in the shine of the wax on the fruit (which should be dull, not shiny) and the appearance of slightly raised ridges that follow the stripes on the watermelon’s rind.”

The Perkins-Veazie system tracks the number of days since transplanting. In North Carolina, the ideal harvest time is typically between 60 and 70 days. Home gardeners should check the instructions on seed packets for the number of days to maturity. Different types of watermelons will have different times to maturity.

You have less information to rely on when buying a watermelon at the market. “In the store, the spin test doesn’t work, but often the first thing I look for is the soil spot,” Perkins-Veazie says. “That’s the yellow spot on the underside of the fruit where it’s been in contact with the ground or plastic. I like to see a deep yellow color there.” Look for a watermelon that feels heavy for its size, which indicates more water.

Check the part of the watermelon that was left on the ground. (Photo by Hoberman) … [+] (Collection/Universal Images Group via Getty Images)

Universal Images Group via Getty Images

Your quest isn’t just to find a ripe watermelon, but to avoid overripe ones as well. “In the field, overripe watermelons will have a stem that’s almost dead. Sometimes there will be sunburn (yellowing on the top of the fruit) as the leaves that shade it die,” says Perkins-Veazie.

Shaker Kousik is a plant pathologist at the U.S. Vegetable Laboratory in Charleston, South Carolina. He’s part of a team that studies diseases, disease resistance, and cultivation of watermelons. He agrees with Perkins-Veazie about checking the tendrils and leaves of a watermelon in the field. He looks for yellow on the underside. “I also tap the watermelon, and if I hear a slight metallic sound, I know it’s ripe,” Kousik says. That advice applies to store-bought melons. “It helps to know that growers usually pick watermelons once they’re ripe in the field,” he says. “I mostly look for the yellow underside and tap the watermelon to hear the metallic sound.”

Watermelons aren’t just delicious, they’re fascinating, and scientists are still learning more about them. For example, we might one day have a ripeness-detection system inspired by coyotes. “One of the most surprising things I discovered in our research plots in Oklahoma is that coyotes can smell when watermelons are ripe, usually a week before we’re ready to harvest them,” Perkins-Veazie says. “I always wanted to understand what compounds they were picking up and develop a simple phone app to signal when the fruit was ready to eat.” Kousik also uncovered some lesser-known facts. Watermelons are native to the desert regions of Africa, and the fruit is related to cucumbers, squash, and pumpkins.

Don’t be discouraged if you follow all the advice and still lose the watermelon lottery. It can happen to the best of us. “I’ve often been wrong about the ripeness of watermelon,” says Perkins-Veazie. Science can help, but there will always be an element of chance when it comes to watermelons.