Q: I’d love some tips on how to grow watermelon. We have two crazy long vines this year, dozens of babies and I want to give ‘em my best shot.
How exciting! Watermelon can be a tricky fruit to grow. But for all of their perceived difficulty I have discovered these wily creatures—with fruit no less—growing freely in abandoned lots and neglected front lawns.
Watermelon is nearly synonymous with a long, hot summer. This represents both the perfect growing condition as well as the time when we most enjoy eating the fruit. You describe what sound like healthy, happy plants, so it’s my guess that a lack of sun and heat are not a problem here. For those who do not have a long growing season, I’d suggest trying shorter-season varieties such as ‘Sugar Baby’ or ‘Northern Sweet’ and/or applying black plastic as a mulch to heat up the soil and extend the season slightly.
A lot of the perceived complication in growing watermelon comes down to their size. They grow on very large and rambling vines that go on to produce monstrous fruit, so it only stands to reason that they require reasonably good soil fertility in order to thrive. It helps to add a generous helping of compost or composted manure to the soil at planting time, as well as a tablespoon of bone meal to the hole. Side dress with compost or bone meal mid-season. Regular applications of sea kelp all season long will help with stress, especially when growing potted plants.
As the name implies, watermelon are full of…well, water, so generous and consistent moisture is required to grow plump and delicious fruit. Erratic watering with periods of drought in between causes stress that can lead to disease and fruit failure. However, they do not like to sit in soggy soil and tend not to fare well in heavy clay or compacted soil that doesn’t drain well. You’re already on the right track if your plants are growing in well draining loam or soil that is on the sandy side.
Another tip to remember around watering is to focus the stream on the soil and roots rather than spraying the leaves. You can also try mulching the soil with straw to help retain moisture and keep the fruit up off of the ground, but make sure to do this only after the soil has had a chance to warm up.
To further complicate matters, too much water can result in tasteless fruit. Be generous during the growing cycle, but pull back on the amount you give just before the fruit begins to ripen and then stop altogether right before harvesting.
Commercially grown watermelons are pruned so that no more than two fruit are grown on each vine. This is done in the service of producing monster melons. If size is of less importance to you, you can choose to let all of your babies grow to maturity. However, when the days begin to shorten and cool, it is best to prune back all new flowers and tiny, new fruit to ensure that the plant’s remaining energy goes directly into bringing the last of the crop to maturity.
Unlike many other fruits, watermelons must be allowed to fully ripen on the vine as they do not increase their sugar content once removed. You’ll know your melons are ripe when the underside turns from white to yellow and the tendril nearest to the fruit dries up. You can also try tapping each melon and listening for the sound they make. Perhaps I lack the finely tuned ear necessary for this method, but I can tap melons until the proverbial cows come home (not a euphemism) and yet I never seem to be able to distinguish the difference between a hollow-sounding ripe fruit and a tinny-sounding unripe fruit.
Garden authority Gayla Trail is the creator of YouGrowGirl.com.