Anytime I’ve purchased watermelon, it is usually cut open and rendered into cubes for eating over the next several days. You can always leave it out and then cut some slices long enough before eating that they can chill a while. At one time I planted watermelon, cut off all but 1 or 2 melons to get them larger. Perhaps left in the skin it may ripen a little. Uncut fruit can be stored in these temperatures for up to two weeks before eating. We opened up a watermelon too early last night. This will accelerate the ripening process. Check every few days to see if the watermelon has ripened. This will accelerate the ripening process. Sweet, juicy watermelon (Citrullus lanatus) is pretty much synonymous with summer, though in warmer parts of the country it can be enjoyed year-round. Wrap cut slices of watermelon in plastic wrap. It is possible to ripen a cantaloupe once it has been cut. Does anyone have a recipe that showcases unripe watermelon to its best advantage? Ripen A Watermelon. It is possible to ripen a cantaloupe once it has been cut. Sprinkle a little pure orange juice over the flesh. I'm pretty sure once you pick a watermellon that's it - you get what you get, not like a banana that will continue to ripen. Store it at room temperature, not in refrigerator. I have purchased a lot of watermelon that isn't fully ripe, it is of poor quality for eating, I have never seen it improve, or ripen more. Once cut, the fruit will last in the refrigerator for only a few days. Sprinkle a little pure orange juice over the flesh. It's perfectly textured, not mealy or anything like that, nicely juicy, just not sweet and not strongly watermelon-flavored yet.