When to plant watermelons in Hawaii
Hawaii is essentially frost-free (USDA zones 9b, 10a, 10b, 11a, 11b, 12a, 12b, 13a), so watermelon timing there is set by heat and daylength rather than frost. As a warm-season crop, the main risk is mid-summer heat — spring and late-summer plantings usually do best.
Hawaii covers a wide range of climates, so your exact frost dates may differ from the state average by two weeks or more. For dates tuned to your town, use the calendar generator.
When to plant watermelons in Hawaii: the short answer
For a spring planting, sow Feb 10 – Mar 1, with seeds started indoors Jan 4 – Jan 18. Wait until the soil is at least 70°F and frost is over.
Your area is essentially frost-free, so planting dates are set by heat and daylength rather than frost. Treat the ranges below as broad season guides.
Warm-season crop: in a frost-free area the main risk is mid-summer heat; spring and late-summer plantings usually do best.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow watermelons in Hawaii, step by step
- Start seeds indoors (Jan 4 – Jan 18). Sow seeds 1 inch deep in seed-starting mix under bright light. They take 4-10 days to sprout, fastest in soil around 85°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 24 inches deep, with a pH between 5.5 and 6.8. Dig in compost before planting.
- Sow outdoors (Feb 10 – Mar 1). Space plants about 36 inches apart in rows 72 inches apart, sowing seed 1 inch deep. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: striped cucumber beetle, aphids, squash vine borer. Diseases and disorders: anthracnose, fusarium wilt, powdery mildew, gummy stem blight.
- Harvest (from about Apr 26 – May 26). Watermelon takes 70-100 days to reach harvest. Longest-season cucurbit here - icebox varieties (70-75 days) are the realistic choice north of the mid-Atlantic. Ripe when the curly tendril nearest the fruit is brown and dry and the ground spot is buttery yellow.
Figures come from our crop data; dates use Hawaii’s average frost dates. More in the full watermelon growing guide.