When to Plant Watermelon in Iowa
The ultimate summer treat. Watermelons need heat, space, and patience — but the payoff is pure joy.
The Short Answer
Iowa Frost Dates
Your planting dates depend on which part of Iowa you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Iowa | 4b, 5a | May 5 - May 20 | Sep 20 - Oct 5 |
| Central Iowa | 5a, 5b | Apr 25 - May 10 | Oct 1 - Oct 15 |
| Southern Iowa | 5b | Apr 20 - May 5 | Oct 5 - Oct 20 |
Watermelon Planting Schedule for Iowa
Northern Iowa (Zones 4b, 5a)
Average last frost: May 5 - May 20 · Average first frost: Sep 20 - Oct 5
Central Iowa (Zones 5a, 5b)
Average last frost: Apr 25 - May 10 · Average first frost: Oct 1 - Oct 15
Southern Iowa (Zones 5b)
Average last frost: Apr 20 - May 5 · Average first frost: Oct 5 - Oct 20
Growing Watermelon in Iowa
Watermelon in Iowa's Climate
Watermelon pushes the limits of cold-climate gardening. Choose short-season varieties only — Sugar Baby (75 days), Blacktail Mountain (75 days, bred for northern conditions). Start indoors 3 weeks before last frost. Black plastic mulch and row cover are essential. Expect smaller fruits than southern growers — but a sun-warmed watermelon from your own cold-climate garden is incomparably satisfying.
Soil Considerations for Iowa
Outstanding black prairie soils. Some of the richest agricultural land in the world. Minimal amendment needed. Make sure soil has warmed to at least 70°F before planting watermelon outside.
Iowa Climate & Growing Season
Continental climate. Cold winters, warm humid summers. Good growing season with adequate rainfall. Watermelon cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.
Growing season length varies across Iowa: Northern Iowa (4b, 5a) has a last frost around May 5 - May 20, while Southern Iowa (5b) sees frost end around Apr 20 - May 5. This difference matters for watermelon — transplant timing shifts by several weeks across the state.
Growing Tips
Black plastic mulch warms soil faster. Check ripeness by looking for a yellow ground spot and listening for a hollow thump.
Companion Planting
Plant watermelon alongside these companions for better growth:
Keep watermelon away from:
The Bottom Line
Last reviewed: March 29, 2026