Raising a World-Class 'Black Diamond' Watermelon

Site Selection and Preparation

• Watermelons are warm-season crops that require full sunlight and plenty of room to grow. These plants perform best in well-drained soils with a sandy loam texture and a pH between 6.0 and 6.5. To improve drainage prior to planting, work about 2 to 3 inches of an organic-matter soil amendment like well-rotted compost into the top 6 to 8 inches of soil . The best way to determine if the pH is too low or too high and the best type of fertilizer to use is to have the soil tested. In the absence of a soil test, work 5-10-10 fertilizer into the top 6 inches of soil at a rate of 3 pounds per 100 square feet before planting.

Spacing and Planting

• Direct seeding of the watermelons is preferred in areas with a long enough growing season, as watermelons do not transplant well, but it is possible to successfully transplant melons that have no more than two or three true leaves and were started in peat or other biodegradable pots to minimize transplant shock. Place seeds or transplants in the garden only after all danger of frost has passed. Each watermelon plant or hill requires about 50 square feet of space, or hills spaced 4 to 5 feet apart in rows 10 to 12 feet apart. Each hill supports two or three transplants. You can sow more seeds than that, then thin out all but the two or three most vigorous seedlings. Plant seeds 1/2 to 1 inch deep or plant transplants at the same depth at which they are currently growing in the medium, breaking off or burying the exposed edges of any peat or other container to avoid a wicking effect. Water in the new seeds or transplants well.

Water That Melon

• Proper watering practices are crucial, as watermelon fruits are made up of mostly water. Watermelons benefit from 1 to 2 inches of water every 10 to 14 days through rainfall and supplemental irrigation. Each deep, infrequent irrigation should moisten the top 6 inches of soil. Overhead irrigation or other splashing water promotes disease spread. Drip or careful hand-watering is preferable. Once fruits begin to ripen, reducing the amount of water supplied encourages better fruit flavor. Excessive rainfall or irrigation when the watermelon is nearly ripe can also cause the fruit to split open.

A Little Side Dressing

• A supplemental fertilizer application with a fertilizer that has a 33-0-0 formula at a rate of 1 pound per 100 feet of row alongside vines as a side dressing before the vines begin to "run" encourages vigorous growth. A second side dressing at the same rate when fruit is developing is also beneficial.

Pull Those Weeds

• Hand-pull weeds that emerge around the vines. Do not hoe or otherwise cultivate them and risk injuring the melon root system. Weeds left around the watermelon compete with the plant for water, light and nutrients and harbor pests and diseases. An organic mulch applied in a layer about 2 inches thick over the ground around the vine once soil temperature rises above 75 degrees Fahrenheit helps conserve soil moisture, regulate soil temperature and suppress weeds.

Prune on a Dry Day

• Cut off any misshapen or rot-affected fruits as soon as you notice them. Once a "Black Diamond" watermelon vine has two or three well-shaped melons developing on the vine, prune off any additional melons that appear. It is important to prune or otherwise work around the plants only when conditions are dry to avoid spreading disease.

Pest and Disease Problems

• Several diseases and pests can potentially impact a prized "Black Diamond" watermelon, threatening plant and fruit quality. Excellent sanitation practices including removing debris from a planting site at the end of the growing season and maintaining a weed-free area around the watermelon plants and broader garden area, as pathogens and pests often overwinter on debris or use weeds as alternate hosts before moving onto watermelons. Fungal diseases can cause young plant death, especially if cool, wet weather occurs after planting. To minimize problems with fungi, cultivate watermelons and related plants in a site only once every three or four years. Avoid overhead watering or otherwise splashing foliage with water, as this promotes the spread of fungal diseases. Aphids, squash bugs and cucumber beetles are among the most common possible pests of watermelon. Healthy, established plants can generally withstand and recover from moderate feeding. Inspect young plants regularly and use a forceful stream of water to knock off the small, soft-bodied aphids; pick off any beetles by hand and drown them in a bucket of soapy water.