Watermelon Seed Starting Tips

Watermelon seedling

Watermelons are a tender, warm-weather crop. Sow watermelon seed or set plants directly in garden in spring 2 weeks after all danger of frost has passed after the soil has warmed to 70°F (21°C).

Watermelon seed can be started indoors 8 to 6 weeks before plants are set out.

For the sweetest flavor, watermelons require a long, hot growing season and plenty of room; watermelon vines require 10 to 15 feet of grow room.

Watermelons mature 70 to 100 frost-free days after sowing depending on the variety.

Sowing and Planting Tips:

  • Grow watermelons from seeds or seedlings.
  • Seed is viable for 4 to 5 years.
  • Start watermelon seed indoors 8 to 6 weeks before transplanting seedlings to the garden; set out transplants 2 or more weeks after the last frost in spring.
  • Sow seed indoors in peat pots filled with seed starting mix. The indoor temperature should be between 80-90°F (27-32°C) until germination. Grow watermelon seedlings at 75°F (24°C).
  • Direct sow watermelons in the garden in spring after all danger of frost has passed and the soil has warmed to 70°F (21°C). In warm-winter regions, sow watermelons in midwinter for harvest in early summer.
  • Watermelon seeds will not germinate at a soil temperature below 65°F (18°C).
  • Sow seed ½ inch (13 mm) deep.
  • Seeds germinate in 3 to 10 days at 80°F (27°C) or warmer.
  • Transplant seedlings to the garden after the soil has warmed to at least 70°F (21°C).
  • Plant on mounds or hills 12 to 24 inches (30-60 cm) high, space mounds 10 feet apart; vines can easily spread 10 to 15 feet.
  • Water to keep the soil from drying.
  • Fertilize with fish emulsion or a soluble complete fertilizer at half strength.
  • Add aged compost to planting beds in advance of transplanting.
  • Watermelons prefer a soil pH range of 7.0 to 8.0.
  • Grow watermelons in full sun for best yield.
  • Avoid planting watermelons where cucumbers or squash have grown recently.
  • Common pest enemies include aphids, cucumber beetles, flea beetles, squash bugs, squash vine borers, slugs, and snails.
  • Common diseases include bacterial wilt, fusarium wilt, downy mildew, powdery mildew, cucumber mosaic.

Interplanting: Plant watermelons with bush beans, corn, dill, eggplant, lettuce, cucumbers, squash, and tomatoes.

Container Growing: Watermelons are not a good choice for container growing. They require significant room to spread and grow.

Recommended Planting Calendar:

  • 8-6 weeks before the last frost in spring: start seed indoors for plants that will be transplanted into plastic tunnel in 4 weeks.
  • 5-4 weeks before the last frost in spring: start seed indoors for seedlings to be transplanted into garden.
  • 4-2 weeks before the last frost in spring: transplant seedlings to plastic tunnel.
  • 1-2 weeks after the last frost in spring: transplant seedlings into the garden.

Recommended varieties: ‘Sugar Baby’ and ‘Sugar Bush’ are small, 8-10 pounds; ‘Fiesta’, ‘Regency’, and ‘Sangria’ are 20 to 25 pounds—all have sweet flavor.

Botanical Name: Citrullus lanatus var. lanatus

Melons are a member of the Cucurbitaceae family; other members cucumbers, squash, watermelon, and pumpkins.