Imagine warm sunshine, a picnic, and a good shade tree. Now, add a juicy, sweet watermelon, picked fresh from your own garden, and you have the makings of a perfect summer day in South Carolina.
Although some gardeners are leery of surrendering the extra space the scrambling vines require, watermelon can be cultivated statewide. Similar to other vegetable crops, they enjoy full sun, well-draining soil with a pH between 5.8 and 6.5, and plenty of water. They are grown easily from seed when planted in warm soil, and coastal residents can begin sowing watermelon patches as early as late-March. Midland folks should plant after April 1, while Upstate gardeners can begin putting seed in the ground after April 20. Planting seeds in mid-June will yield a strong late-season harvest in all regions.
Gardeners can get a jumpstart on the growing season with transplants, and in the process, beat their neighbors to harvest by about two weeks. Covering prepared soil beds with black plastic mulch before planting will warm the soil, naturally promote faster growth and put fruit on the table another week or two ahead of the competition. Simply punch a hole in the plastic for each transplant.
Give watermelon vines plenty of space. Traditional varieties like Charleston Gray or Crimson Sweet should be planted 5 to 6 feet apart in rows spaced 6 to 8 feet apart. If you’re short on space, try the Sugar Bush variety, which needs just 6 square feet per vine.
Fertilize your crop before planting based on soil test results. Lacking a test, 30 pounds of 5-10-10 fertilizer per 1,000 square feet should suffice. Several weeks after planting and just before the vines start to “run,” sidedress the plants with 2 pounds of calcium nitrate per 100 feet of row.
The hardest—and most important—part of growing watermelons is irrigation. As you can guess from the name, watermelons need a lot of H2O and the best way to provide it is with drip irrigation. Unlike sprinklers, drip applies water directly at the plant’s roots and not on the foliage, making irrigation more efficient and less likely to cause disease problems. Adequate water is especially important during fruit development, so irrigate once or twice per week depending on rainfall. Wet the soil at least 6 inches deep at each watering and avoid any prolonged dry spells.
Harvesting watermelons can be tricky, but there are several ripeness indicators to look for. You’ll know it’s time to plan that picnic when the vine tendril closest to the fruit turns brown and the underside of the fruit changes from bright white to pale yellow. And don’t forget the time-honored “thump test”: When thumped a ripe melon will give a dull thud, while an immature fruit produces a ringing, metallic sound.
Follow these tips and you’re bound to enjoy vine-ripe watermelons by season’s end. For more information on growing watermelons and other crops visit Clemson Extension’s Home & Garden Information Center at clemson.edu/hgic.
S. Cory Tanner is an area horticulture agent for Clemson Extension based in Greenville County. His responsibilities include coordinating the Greenville County Master Gardener program and providing home gardening advice. Contact Cory at shannt@clemson.edu.