When to plant watermelons in New Hampshire
New Hampshire’s average last spring frost is May 13, and the first fall frost typically arrives around September 25 — about 135 frost-free days (USDA zones 3b, 4a, 4b, 5a, 5b, 6a). Watermelon needs 70–100 days to mature, which fits comfortably within New Hampshire's growing season.
When to plant watermelons in New Hampshire: the short answer
For a spring planting, plant out May 20 – Jun 6, with seeds started indoors Apr 15 – Apr 29. Wait until the soil is at least 70°F and frost is over.
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 New Hampshire, step by step
- Start seeds indoors (Apr 15 – Apr 29). 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.
- Plant out (May 20 – Jun 6). Space plants about 36 inches apart in rows 72 inches apart. 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 Aug 5 – Sep 4). 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 New Hampshire’s average frost dates. More in the full watermelon growing guide.
Watermelon planting dates by USDA zone in New Hampshire
New Hampshire spans USDA zones 3b, 4a, 4b, 5a, 5b, 6a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the watermelon dates shift with them.
When to plant watermelons in nearby states
| State | Last frost | Plant out |
|---|---|---|
| New Hampshire (this page) | May 13 | May 20 – Jun 6 |
| Maine | May 14 | May 21 – Jun 7 |
| Vermont | May 14 | May 21 – Jun 7 |
| Massachusetts | April 24 | May 1 – May 18 |
| Rhode Island | April 25 | May 2 – May 19 |
| Connecticut | April 25 | May 2 – May 19 |
| New York | May 1 | May 8 – May 25 |
Questions gardeners in New Hampshire ask
When is the best time to plant watermelons in New Hampshire?
Plant watermelon transplants outdoors in New Hampshire between May 20 and June 6. That timing is set by New Hampshire's average last spring frost of May 13.
When should I start watermelon seeds indoors in New Hampshire?
Start seeds indoors between April 15 and April 29, about 3 weeks before the last frost, so the seedlings are ready to plant out from May 20.
What is the latest I can plant watermelons in New Hampshire?
About July 17. Watermelons need at least 70 days to mature, and frost around September 25 ends the season, so later plantings risk being cut short.
When will watermelons planted in New Hampshire be ready to harvest?
Planted on time, watermelons are usually ready from about August 5 to September 4, 70-100 days after planting.
When is the last frost in New Hampshire?
On average around May 13, with the first fall frost around September 25 - about 135 frost-free days. Your town may differ by two weeks or more.