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I planted watermelons for the first time this year. They seem to be growing just fine, but I know the hard part will be knowing when they're ripe.
Horticulturist Jonathan Schultheis at North Carolina State University says determining when a watermelon is ripe is almost an art, especially with so many varieties. However, one general sign of ripeness is where the plant connects to the fruit.
"That first node, or knuckle, as you might want to call it where the stem is attached to the fruit, there's a little curly-cue or tendril," he says "And if you look at that, and that has dried up, that's a pretty good indicator that that particular melon is ripe."
Another indicator is on the underside of the fruit. A ripe melon usually has a yellowish belly. If it's white, it's not ready yet. Some striped varieties are a darker green, and as the fruit ripens, the stripes will separate, and a lighter-green color becomes more visible. By contrast, other varieties take on a duller appearance.
Your grandmother would "thump" the melon. If you hear a dull thud pick it, and if you hear a metallic ring, it's not ripe. But Schultheis says a dull thud isn't always reliable.
"There may be something where there's a hollowing inside the fruit, something called "hollow heart". And so it may just not be filled in as well, and yet it might not even be ripe. So you'll get that sort of dull-thuddy sound, and you'll think it's ripe but it may not be," he says. "This could be used to some extent, although it's not a great indicator because there's some of these other things I just mentioned earlier that are probably better."
The only way to really tell if a watermelon is ripe is by cutting one open. Once off the vine, it does not continue to ripen, and you can store watermelon for up to three weeks in a cool place.