What is the correct time to pick a watermelon?
When the tendrils around the fruit begin to die off, nutrients are no longer reaching the fruit and ripening is complete. A ripe watermelon has a duller surface, and any parts that were in contact with the ground turn a pale green or yellow. Gardeners can also test for ripeness by smacking the fruit with their palms. If the fruit makes a hollow sound, it is probably ripe. Not all ripe fruits make this sound, however. Source: gardeningknowhow.com