I have several watermelon plants in my veggie patch this year. They are doing well; no bugs or anything (except the bees!). My watermelons are about the size of a dinner plate, maybe 9 inches in diameter, they're very round, not oval. My greatuncle has a watermelon farm, and he always said you can tell when a watermelon is ripe for picking by knocking on it. If it is hollow sounding, it's ripe.
So I gave some of my melons a whack and what do you know, it sounded hollow. I tapped an immature one too, and it just made a thud. Only problem is, my watermelons are only 9 inches! Maybe they're just going to be runt sized this year. I'm starting to wonder if they're maybe not ripe. Anybody heard of this tapping watermelon theory?