Watermelon is one of those crops that, once you grow it at home, the store-bought version forever pales in comparison. In addition to being delicious, watermelon is a good source of Vitamin C and other nutrients, and as the name suggests, hydrating. And, did you know that watermelon has more lycopene than any other fresh fruit or vegetable? Lycopene is an antioxidant linked to decreased risk of cancer, heart disease, and age-related eye disorders. Sweet, delicious, and nutritious, homegrown watermelon might just be the perfect summertime snack. Some backyard gardeners shy away from growing watermelon because of how much space it takes up, but the benefits can be worth it - not to mention that the fun of a good seed spitting competition is a dying art form.
Can I Grow Watermelon in my Garden?
Watermelons will grow throughout most of the contiguous United States, although growers in northern zones or high elevation should take care to select a variety with a relatively short days to maturity period. Generally speaking, smaller-fruited varieties ripen quicker. The most important thing is to wait until the weather is warm enough to plant melons outside in your area. Two weeks after the average last frost date is a good rule of thumb. Watermelon plants are not cold tolerant in the slightest, so don’t jump the gun!
If you want to grow watermelon, but space is a concern, choose a variety with “bush” in the name. Their vines will be much shorter than traditional vining types, which can easily sprawl up to six feet or more. Bush type watermelons only need about three to four feet between plants to thrive. Alternatively, you could try growing your melons on a very sturdy trellis, though watermelons are not natural climbers, so you’ll need to help them along with clips or ties to attach the vines to the trellis, and fruit slings to support the melons as they grow.
How to Plant and Care for Watermelons
Watermelons are heavy feeders, so prep your soil by mixing in 1-2 inches of compost. Melons of all kinds are traditionally planted on the top of low hills made up of either your existing garden soil or with a couple shovels of compost on top of your prepared garden space. Form your hills about 6 feet apart. Growers in cooler zones may find it helpful to cover the soil with black plastic or dark mulch to help warm it up, since watermelon seeds need about 70° soil to germinate. When your weather is consistently above 60° F at night and 80° or higher in the daytime it’s time to plant. Plant 4 to 8 seeds per mound, about ½ inch deep, and water thoroughly. You should see sprouts emerging within 3 to 10 days. As soon as the seedlings have grown two sets of true leaves (the shaped leaves that come out after the first round seed leaves), remove all but the two strongest looking plants per mound.
As your plants grow, it’s very important to keep the plants well-watered. It’s best to water at the base of the plant, and preferably in the morning, to keep the foliage and soil surface from staying wet too long. Wet leaves and soil can invite fungal disease. As fruits form, place several inches of straw under each developing watermelon. This will keep the fruit off of the ground and help prevent rotting. Feed the plants with your favorite, water-soluble, all-purpose fertilizer every 2-4 weeks. Harvest melons when the curly tendrils closest to the fruit are brown and shriveled and/or the fruits sound hollow when tapped.
What about transplanting watermelon seedlings?
Watermelons do best when direct seeded, but if you need to extend your season by starting seeds indoors, or are just tempted at your local nursery, look for small plants with deep green, healthy looking leaves. Young plants in 4-6” pots have less chance of suffering from transplant shock. Avoid plants that are already flowering, are leggy, or have visible roots extending through their drainage holes. If starting your own seeds indoors, aim to have your plants no more than 4-6 weeks old when you transplant them outside.
Striped Cucumber Beetle, photo by Scott Bauer, USDA ARS Image Archive
Pests and Problems to Watch Out For
- Hard soil: If you have clay or compacted soil, take extra care to loosen the soil and amend it with plenty of organic matter. Watermelon plants really struggle in heavy or water-logged soils.
- Striped cucumber beetles: These small yellow beetles with black stripes do damage to plants in their own right, but the worst thing about them is that they are carriers of a disease called fusarium wilt, which causes vines to abruptly wilt and stop growing. Remove and destroy (not in your compost pile) any plants that suddenly wilt in this way. It’s a good idea to cover young plants with a floating row cover to keep beetles away. Make sure to remove your cover when the vine starts to flower, so that insects can pollinate the flowers
- Insufficient water: Vines that don’t get enough water may grow slowly, not set very many fruits, or have very small fruits.
- Blossom end rot: This phenomenon is when a previously nice looking melon turns black on the end and begins to rot. Generally, this means the fruit didn’t get enough calcium at a critical point in development, which can happen for several reasons: a lack of calcium in the soil, insufficient water preventing the plant from taking up calcium, or an overabundance of nitrogen, causing the plant to divert calcium to leaf growth. Avoid the heartbreak by amending your soil with compost before planting, keeping your melon patch consistently watered, and applying a balanced fertilizer every 2-4 weeks.