Shop in watermelon season. The only way to guarantee you'll get ripe, delicious fruit.  Look for the field spot. Most watermelons will have a patch on the bottom, where it rested on the ground before being picked. If the patch is yellow, the watermelon is ripe. If it's white, it's unripe. Inspect the weight. A ripe watermelon should feel heavy for its size, so give those muscles are workout and lift those melons. Finally, give it a gentle thump. A ripe watermelon will sound hollow when thumped lightly (our family's favourite method).