Watermelon is a warm season crop that grows well in the warm, dry days of Kansas summers. The plant grows best in deep, sandy soils; however, small icebox-type watermelons can be grown on upland shallow soils. Most watermelons require a lot of room and are not well adapted to small backyard gardens.
Variety considerations. There are a wide range of watermelon varieties, with many different fruit characteristics that will perform well in Kansas. Fruit shape and size, rind color, and flesh color can all be taken into consideration. Varieties with good disease resistance are also beneficial. For gardeners with small spaces, newer varieties with more compact vines have been developed.
Seedless watermelon. Seedless watermelons are produced by growing a specially developed cultivar that is cross-pollinated by a regular cultivar or a provided pollinator variety. Because two varieties are required to produce the seedless fruit, the amount of space needed is not practical for most home gardeners. The seedless cultivars are also less vigorous and more finicky than regular seeded watermelons.
When to plant. Watermelons thrive in warm soils and warm air temperatures. Plant after all danger of frost is past in early to mid-May, when soil temperature is at least 60°F and air temperatures are consistently above 70°F.
Spacing. Standard watermelons require about 50 square feet per plant or hill — 4 to 5 plants together, then thin to the strongest 2 plants after two true leaves have developed. Plant 4 to 5 feet apart in rows 10 to 12 feet apart. Small-vined icebox varieties can be spaced closer together, using 2 to 3 feet between hills in rows 5 to 6 feet apart. Closer spacing of large-vined, large-fruited melons will likely reduce the overall fruit size but may be a good option if garden space is limited.
Crop rotation. If possible in your garden space, do not plant watermelons in the same area where cucumbers, melons, squashes, or pumpkins have been planted in the past 3 to 4 years.
Care. Watermelons need a warm, sunny, well-drained growing area. If your garden soil is heavy, plant on ridges or raised beds to improve the soil drainage. Black plastic mulch can help warm the soil, conserve water, and suppress weeds in watermelon plantings. If straw mulch is used, do not apply it until the soil is warmer than 75°F.
Watermelons can be grown as transplants and transferred to the garden. Use a fairly large transplant or peat pot container for best results to avoid disturbing the roots when transplanting.
Row covers may be useful to reduce cucumber beetle damage in the early season but must be removed once the plants start flowering. Row covers can also help increase the success of transplanting due to protection from the wind. Weeds are difficult to control in sprawling vines, making early season weed control essential. Scrape weeds using shallow cultivation close to the plants.
Like cucumbers, cantaloupe, squash, and pumpkin, watermelons have separate male and female flowers on the same plant. Bees are necessary to transfer pollen from the male to female flowers.
Watermelons need plenty of water during early growth, flowering, and early fruit development. Once the melons have reached full size but have yet to ripen, watering should be minimized to encourage sweet, flavorful fruit with high sugar content.
Harvesting. Watermelons are ready for harvest when the underside of the fruit turns a bright buttery yellow color and when the small, curled tendril where the fruit attaches to the vine has turned brown and died. Thumping larger fruited varieties produces a dull, hollow sound when ripe; however, small icebox types are difficult to thump to determine ripeness.
