Plant watermelon seeds in the garden when the soil temperature reaches 70°F (21°C), usually 2 to 4 weeks after the last frost in spring. Watermelon is a tropical plant and demands a long, warm, dry growing season with temperatures between 70° and 80°F (21-26°C) during the day and 60°-70°F (16-21°C) at night. Watermelons require 75 to 90 days to reach harvest.
Watermelon seeds can be started indoors with bottom heat and a soil temperature of 75°F (24°C). However, watermelons started indoors will not develop the deep taproots of direct-seeded plants. The unnatural root development on transplants means more irrigation will be required once transplants are set in the garden.
Grow watermelons in light, fertile, deep loam, or sandy soil. The soil should be well-drained. Add aged compost or well-rotted manure to the soil and turn the soil to a depth of 8 inches (20cm) or more. Watermelons are heavy feeders. Add bone meal, greensand, or granite dust to the planting hole.
Planting watermelons on mounds or hills is one way to ensure the soil is sufficiently warm for watermelons. The higher the mound the warmer the soil. Vines can also be trained down and around the hill rather than letting them run through the garden. Vines commonly grow 6 to 12 feet (2-4m)long. Some small varieties can be grown in a container or trained to a trellis.
Watermelons are ripe when they make a “punk” sound when struck by knuckles. A “pink” or “pank” sound means the melon is not ripe—according to Mark Twain.
Melon planting dates
(These dates are for the Northern Hemisphere)
|Average date of the last frost||Planting dates|
|Jan. 30||Feb. 15-Apr. 1|
|Feb. 8||Feb. 15-Apr. 15|
|Feb. 18||Mar. 1-June 1|
|Feb. 28||Mar. 10-June 1|
|Mar. 10||Mar. 20-June 1|
|Mar. 20||Apr. 1-Jun3 1|
|Mar. 30||Apr. 10-June 15|
|Apr. 10||Apr. 20-June 15|
|Apr. 20||May 1-June 1|
|Apr. 30||May 10-June 1|
|May 10||May 20-June 10|
|May 20||June 1-20|
Watermelon planting details
- Sowing depth: ½ -1 ½ inches (12mm) or slightly more
- Space between plants after thinning: 2-6 feet (30-45cm)
- Days to sprout: 4-10
- Days to harvest: 75-90
- Storage period: 1 week refrigerated
- Seeds per 100-row feet: 1 ounce
- Suggested varieties: Black Diamond (90 days), Charleston Gray (85 days), Crimson Sweet (80 days), Sugar Baby (75 days).
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