I always check the bottom of a watermelon. It should be yellow where it has laid on the ground. The more yellow, the better the melon.
The "bottom" of the watermelon (the side that was lying on the ground while it was growing), is usually a white color. When it has turned a deep, creamy yellow, the watermelon is ripe.
To select a watermelon, I use the thumping method by knocking on one with my knuckles. If it has a hollow sound to it, it usually is very sweet.
I always thump the watermelon to tell if its ripe. If it sounds hollow like a loaf of home baked bread then its ripe. I have never had a bad watermelon with this technique!
Choosing Watermelons. When choosing a whole watermelon, I always thump the melon with my fingers. The one that I choose has to sound "hollow". . .
The best tip I heard for choosing a ripe watermelon, is to find the darkest green one you can find without any bruises or soft spots.
The best tip I ever got came from a man I met in a grocery store. He was standing there by the watermelons trying to balance a broom straw on a watermelon.
As watermelon season wraps up, we are seeing tons of them on sale. You want to make sure you choose a good one, or else you'll be stuck with 15 pounds of lackluster fruit. The key to finding a good one by sight is looking for a rather ugly one that has a big yellowish patch on one side.