There is an article on our EarthBox Blog:
https://blog.earthbox.com/growing-watermelon-in-earthbox There is some great information in here.
When your watermelon is ready to harvest will depend on which variety you choose to grow. On average, you should expect to harvest approximately 60 to 90 days after planting, or about 45 days after you see fruit develop. Look for visual cues to determine when the fruit is ready to be picked, such as the color of the rind and the vine’s tendrils. The rind will change from bright to dull green as it ripens, and its belly will turn from white to yellow. The tendrils will also begin turning yellow, eventually to brown. You can also test for ripeness by the sound made when tapping on the melon. Under-ripe fruit will make a higher pitched sound, and the pitch will lower to a dull thud as the melon ripens. Ripening on the vine takes about two weeks, so as you start noticing these changes in the fruit, you can decide if you want to withhold water for the last week before the melon is fully ripe. Withholding water helps concentrate the sugars, which is what makes the melons so sweet. Too much water during the ripening phase can lead to bland, tasteless watermelons.
Once your fruit is ready, you can cut it right off the vine! Your watermelons will keep for two to three weeks on the counter, and even longer if you store them in the refrigerator. You can also freeze some of the fruit for use in slushies to help you stay cool in the heat!
