Watermelon plants produce fruit with a tough green rind and a juicy red interior. They are suitable for gardens with long, warm, growing seasons, and there are many varieties that ripen at different times, allowing for a long harvest throughout the season. Do not assume that a watermelon is ripe simply because it looks like it is. There are several factors to take into account before cutting a watermelon from the vine.
Look at the surface of the watermelon. While an immature fruit is glossy and shiny, a mature watermelon has a slightly dull finish on the green rind.
Scrape the rind lightly with your fingernail. The rind of a ripe watermelon is tough and resists marking while an immature watermelon is easy to scrape.
Turn the watermelon over and look at the bottom. In a ripe melon, the bottom of the fruit, where it sits on the ground, turns from light green to a yellowish color.
Look at the curly tendrils on the vine close to the watermelon. In an immature watermelon, these curly tendrils are lush and green, while on a mature watermelon, the tendrils are brown and dry to the touch.