We have tried several ways to tell if a watermelon is ripe, and found that the most reliable (still not 100%, but pretty good) is to look at the curly tendrils on the vine. When the two that are towards the base of the plant (roots) from the watermelon have turned brown and withered, the watermelon should be ripe. However, if you are having a very cool, wet, and/or disease-ridden year, the tendrils will sometimes brown before the watermelon is fully ripe. If you suspect this, then wait another week or two before harvesting. We find the method of tapping on the watermelon to hear if it sounds hollow is not a reliable method for us. Even though no method is totally foolproof, the tendril method is the best we’ve experienced.
Other watermelon tips:
- If you have warmer areas, such as south-facing slopes or slightly rocky soil areas in your garden that is a good place for your watermelons. (Stones in your soil help the soil warm up faster, and hold warmth, so we value our stony soil even though they make cultivation difficult.) However, make sure you rotate your annual crops to different beds/areas each year to reduce pest, weed, and disease build-up in the soil!
- Make sure the soil is warm before you sow your watermelon. We start ours indoors, but it needs to be pretty nice and warm, even at night, or some will sulk. Mice really love watermelon seeds, so make sure they can’t reach yours! if you are only starting a few plants, and are worried about mice, put a large, mesh strainer inverted over your seed pots until the seedlings are up and have their first true leaves. (We’ve had mice eat the seeds as they sprouted, and even after they sprouted!)
- Be patient. Although many of us associate watermelons with early July, here in the North we often eat ours around Labor Day, and often we’ve kept the late-harvested melons in the fridge into October. While a few early melons can ripen here in August, the majority will be ready in September, having been planted out in late May. If you have frost free/warm dates that begin in April, you may be able to get the majority of your harvest in August, or and even a few in mid to late July.
- When you plant or sow out your watermelons, keep them covered for the first weeks! This not only gives them a little extra heat that they love, but also keeps pests away, so they have a better chance to thrive. That said, you will need to uncover them before (or immediately when) they start to flower, otherwise the fruits will not be pollinated!
- Some watermelons will pop or crack open if they receive very heavy watering (rain) after a period of little water or if they are already pretty well ripe. Keeping even water during the fruiting process will greatly help with this, and also help the fruit develop properly.