When to plant watermelons in North Dakota
North Dakota’s average last spring frost is May 15, and the first fall frost typically arrives around September 20 — about 128 frost-free days (USDA zones 3a, 3b, 4a, 4b). Watermelon needs 70–100 days to mature, which fits comfortably within North Dakota's growing season.
When to plant watermelons in North Dakota: the short answer
For a spring planting, plant out May 22 – Jun 8, with seeds started indoors Apr 17 – May 1. 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 North Dakota, step by step
- Start seeds indoors (Apr 17 – May 1). 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 22 – Jun 8). 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 7 – Sep 6). 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 North Dakota’s average frost dates. More in the full watermelon growing guide.
Watermelon planting dates by USDA zone in North Dakota
North Dakota spans USDA zones 3a, 3b, 4a, 4b. 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 |
|---|---|---|
| North Dakota (this page) | May 15 | May 22 – Jun 8 |
| South Dakota | May 10 | May 17 – Jun 3 |
| Nebraska | April 30 | May 7 – May 24 |
| Kansas | April 15 | Apr 22 – May 9 |
| Oklahoma | April 1 | Apr 8 – Apr 25 |
Questions gardeners in North Dakota ask
When is the best time to plant watermelons in North Dakota?
Plant watermelon transplants outdoors in North Dakota between May 22 and June 8. That timing is set by North Dakota's average last spring frost of May 15.
When should I start watermelon seeds indoors in North Dakota?
Start seeds indoors between April 17 and May 1, about 3 weeks before the last frost, so the seedlings are ready to plant out from May 22.
What is the latest I can plant watermelons in North Dakota?
About July 12. Watermelons need at least 70 days to mature, and frost around September 20 ends the season, so later plantings risk being cut short.
When will watermelons planted in North Dakota be ready to harvest?
Planted on time, watermelons are usually ready from about August 7 to September 6, 70-100 days after planting.
When is the last frost in North Dakota?
On average around May 15, with the first fall frost around September 20 - about 128 frost-free days. Your town may differ by two weeks or more.