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Historical frost averages plus extension guidance, not a forecast. Check the forecast and soil temperature before planting.
Sow or plant watermelon outside 2–4 weeks after your last spring frost, when the soil has warmed to 70°F or more. If your season is short, start seeds indoors 1–2 weeks before your last frost, so they're 3–4 weeks old at planting. Watermelons need heat and a long season, so don't rush them into cold ground.
- Frost tolerance
- Very tender: no frost
- Soil temperature
- Sow at 70–95°F (min 60°F)
- Days to harvest
- 70–100 days from seed
The rule we use
- Start seeds indoors: 1–2 weeks before the last spring frost
- Sow outdoors: 2–4 weeks after the last spring frost
- Plant out: 2–4 weeks after the last spring frost
Why watermelons wait
Watermelons are one of the most heat-loving crops in the garden. Seeds rot in cold, wet soil, and plants set out too early sit still or get chilled. Extension guides put them a couple of weeks after other tender crops like beans and tomatoes for this reason.
Check the soil before sowing. Below 60°F, seeds barely germinate; at 70–90°F they come up in under a week.
Starting seeds indoors
Watermelons hate having their roots disturbed, so start them only 3–4 weeks before planting out, in individual pots at least 3–4 inches wide. Peat or paper pots that go straight into the ground work well. Keep them warm, around 80°F, until they sprout; a heat mat helps.
Harden them off for about a week, then plant without breaking up the root ball. Older, root-bound seedlings often stall after planting.
Tips for short seasons
Most full-size watermelons need 80–100 warm days. In northern areas, pick small "icebox" types that ripen in 70–80 days. Lay black plastic a week or two before planting to warm the soil, and use row cover for the first few weeks.
Take the row cover off when female flowers open so bees can pollinate them. A melon is usually ripe when the curly tendril nearest it turns brown and the spot where it rests on the ground turns from white to creamy yellow.
Seeds and supplies for watermelon
- Watermelon seeds at True Leaf Market
- Park Seed for seeds and young plants.
- Seedling heat mats keep seed trays warm for fast, even sprouting.
- A soil thermometer to check the soil is warm enough before sowing.
- Floating row cover for warmth in the first weeks after planting.
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Questions about planting watermelon
When should I plant watermelon seeds outside?
About 2–4 weeks after your last spring frost, once the soil is at least 70°F. Enter your ZIP above to see the dates for your area.
Can I plant watermelon in June?
Often yes. Count the days from planting to your first fall frost and compare it with the days to maturity on the seed packet. If there's a margin of a couple of weeks, go ahead.
Should I start watermelon indoors or sow it directly?
Sow directly where the summer is long and hot. In cooler areas, starting indoors 3–4 weeks ahead gains time, but handle the roots gently.
Sources
- Vegetable Planting Calendar for Central Maryland (2026), University of Maryland Extension
- Vegetables for Spring and Fall Planting; Vegetables for Summer Planting, University of Maryland Extension Master Gardeners
- Vegetable Planting Guide (CMG GardenNotes #720), Colorado State University Extension
- Soil temperature conditions for vegetable seed germination, Oregon State University Extension
- Extension Gardener Handbook, Ch. 16: Vegetable Gardening, NC State Extension
- Suggested Vegetable Planting Dates for Utah, Utah State University Extension
- Frost dates: NOAA NCEI U.S. Climate Normals 1991–2020 (doi:10.25921/4ek7-fk11)