Many home gardeners experience difficulty in determining when watermelons are ripe.
Use a combination of the following indicators:
(1) light green, curly tendrils on the stem near the point of attachment of the melon usually turn brown and dry;
(2) the surface color of the fruit turns dull;
(3) the skin becomes resistant to penetration by the thumbnail and is rough to the touch; and
(4) the bottom of the melon (where it lies on the soil) turns from light green to a yellowish color.
These indicators for choosing a ripe watermelon are much more reliable than "thumping" the melon with a knuckle. Many watermelons do not emit the proverbial "dull thud"when ripe. For these, the dull thud may indicate an over-ripe fruit.