Florida is a leading watermelon state and the only one that ships melons from December to April. In the home garden the vines need a lot of room, more than 18 to 24 square feet per plant, though small 'icebox' varieties help. Gummy stem blight is the disease to watch for, and bees are needed for fruit to set.1, 2
direct seed (or containerized transplants with developed roots)
Seed depth (inches)
1 1/2 to 2
Spacing in the row (inches)
24 to 48
Between rows (inches)
60
Days to harvest
80 to 100 from seed; 60 to 90 from transplant
The Florida Vegetable Gardening Guide gives late March to April or July to August in North Florida, January to March in Central Florida and December to March in South Florida; Gardening Solutions says March and April in the north, January through March in Central and South Florida, and December again in the south. Roots are sensitive, so if you use transplants, choose ones grown in peat pots that go into the ground whole. Gardening Solutions' rule of thumb when the seed packet gives no spacing: plants 36 inches apart in rows 7 to 8 feet apart. 'Seedless' types must be planted alongside regular seeded types to set fruit reliably.
Avoid stressing plants with too much or too little water; stress from water, pests, weeds or poor nutrition lowers flavor.
Grows in almost any well-drained soil. Best daytime temperatures are 70 to 85 F, with up to 90 F tolerated. Bees are required for pollination. Choose disease-resistant varieties. The heirloom 'Moon & Stars' is a large type for gardens with plenty of space.
Gummy stem blight (black rot): A major fungal disease of watermelon. Buy seed from a source with a record of clean seed, check transplants for dead leaf edges, water-soaked stems or gummy ooze, keep debris from other cucurbits away, and rotate so watermelon or other cucurbits have not grown there for two or three years. EDIS PP280 notes the fungus survives on seed, weeds and old cucurbit debris and thrives in Florida's humid nights.
Powdery mildew and downy mildew: Can also cause problems; preventive fungicides may be needed in some areas.
Watermelons take about 80 to 100 days to mature. A ripe melon has a cream-colored or bright yellow patch where it rests on the ground (white or pale green means not yet), and the curly tendril nearest the melon turns brown and dries. Avoid wounding fruit at harvest. Melons keep a little over a week at room temperature or about two weeks refrigerated; storing at 45 to 50 F helps prevent black rot after harvest.
The FAO manual does not give watermelon its own entry. In its cucumber entry it groups melons with squash and zucchini as high-value summer crops that suit media beds because of their large roots, and notes that cucurbits need a lot of nitrogen and potassium, so plant numbers should match the fish stock (p. 173). SRAC 454 does not mention melons.
What this lesson doesn't cover yet
No UF/IFAS home-garden soil pH or fertilizer rate for watermelon was found.
Spacing differs: SP 103 gives 24 to 48 in between plants and 60 in between rows; Gardening Solutions gives 36 in and 7 to 8 ft.
Your county extension office and its Florida Master Gardeners can fill these in for your garden.