Watermelons:
Look at the outside of the watermelon.
The first thing to notice is the color. Naturally ripe watermelons are a dull green, without excessive shine. The green should be relatively dark. On the other hand, if the watermelon has a grayish hue or is very light green, it may be less sweet and its flesh may be flavorless.
Look at the yellow part of the watermelon.
The yellow part of the watermelon, often found at the base, is a good indicator of ripeness. This is the area that touches the ground during growth. If it’s yellow, it’s a good sign; it means the watermelon has ripened naturally. On the other hand, a watermelon with this white area may still be unripe.
Look at the watermelon’s marbling.
Marbling or streaks on a watermelon can also indicate its quality. Watermelons with dense, even marbling are typically sweeter and juicier. However, if the marbling is sparse or broken, there’s a good chance the watermelon isn’t ripe enough.
Check the navel of a watermelon.
A watermelon’s navel can also indicate its quality. You’ll notice that some navels are large, others small. It’s recommended to choose watermelons with a small navel. The smaller the navel, the thinner the skin, indicating good ripeness. A watermelon with a large navel may have been picked too early or chemically treated.