May 31, Four tips on how to choose a watermelon, know when a watermelon is ripe, and what to do with ripe and under-ripened watermelon. May 21, Give it a thump: Tap the underbelly of the watermelon. A ripe one will have a deep hollow sound. Under-ripe or over-ripe melons will sound dull. Although it can be difficult to know how ripe the interior is just by inspecting the outside, there are several clever tricks you can learn to help you pick the. If You Open a Watermelon and See This, Throw It Out! May 31, How To Pick The Perfect Watermelon - Across America, US - Meh. Some people swear by thumping the melon to determine how ripe it is, but. Jun 27, Here are the best tips for how to pick a good watermelon that's ripe and sweet, like finding the field spot and pollination points. Learn all about watermelon, including how to choose a ripe one, how to store it properly, and how to use it in recipes all summer long.