Watermelon (Citrullus lanatus) is a warm-season frost-tender annual plant that produces large, juicy fruits late in the summer. The fruits may be round or oblong, have pink, red or yellow flesh and solid, marbled or striped skins. Some seedless varieties exist, but these are not truly seedless as they have thin, white edible seeds in the flesh. For optimum fruit production, watermelon requires just the right environment.
Watermelon plants love the heat, and need a long and warm growing season of at least 70 to 85 days, depending on the variety, to produce sweet fruit. They grow best when daytime temperatures fall between 70 and 80 degrees Fahrenheit, and nighttime temperatures fall between 65 and 70 degrees Fahrenheit. They can thrive in both humid and semi-arid environments, but may develop fungal foliage diseases in humid areas more frequently than in dry areas. Watermelon plants need an area with full sun to develop completely.
Watermelon grows best in fertile, well-draining, sandy loam soils. Most soils benefit from incorporating a few inches of organic compost before planting, and perhaps some fertilizer as well. Avoid very sandy or clay soils, as they will stunt the growth of watermelon if not handled properly. Keeping weeds down around the melons from planting to harvest will reduce competition for water and nutrients. A 2- to 3-inch layer of mulch around the bases of the plants can help with weed suppression with little manual labor. After growth emerges, the plants may benefit from a side dressing of 33-0-0 or 21-0-0 fertilizer to encourage strong growth. Some already rich soils may not require this extra boost.
Watermelon plants need lots of space to grow and spread out. If you start seeds directly in the ground, build mounds in your garden, spacing them 4 to 6 feet apart. Plant four to six seeds per mound; when the seedlings develop two leaves, thin them to two plants per mound. If you decide to start the seeds indoors and transplant them outdoors after some growth, plant them in rows instead. Generally, watermelons have two types of growth habits: bush and vine. The bush varieties can grow 2 feet apart in rows 4 to 6 feet apart. Vining varieties may require 5 to 6 feet between each plant and 6 to 8 feet between each row.
Although the watermelon's deep root system makes it relatively drought-tolerant, the plant requires an abundance of water to produce healthy fruit. Keep the soil consistently moist from planting until the fruit reaches the size of a tennis ball. After that point, water when the top of the soil feels dry to the touch. This plant can easily develop fungal foliage problems, so if you must water overhead, do so in the morning so that the foliage has a chance to dry during the day. Drip irrigation can eliminate, or greatly reduce, this problem. Each time you water, water deeply to a depth of at least 6 inches.
- University of Illinois Extension: Watermelon
- Ohio State University Extension: Growing Watermelon in the Home Garden
- Utah State University Cooperative Extension: Watermelon in the Garden
- UC Vegetable Research and Information Center: Watermelon Production in California
- Clemson Cooperative Extension: Watermelons
- Cornell University Growing Guide: Watermelon
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