When to plant in Ottumwa, IA
USDA Zone 5bHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Ottumwa, Iowa — all computed from Ottumwa's nearest NOAA weather station.
Zone 5b means Ottumwa sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
Frost probability
OTTUMWA INDUSTRIAL AP · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Ottumwa’s own odds, recorded at OTTUMWA INDUSTRIAL AP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 16 | May 3 | Apr 18 | Sep 19 | Oct 3 | Oct 17 |
| 32°F | May 7 | Apr 23 | Apr 9 | Sep 29 | Oct 14 | Oct 26 |
| 28°F | Apr 28 | Apr 13 | Apr 1 | Oct 10 | Oct 24 | Nov 5 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Ottumwa, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 31 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Ottumwa planting FAQ
When is the last spring frost in Ottumwa, IA?
Ottumwa's average last spring frost falls near April 23 — the 50% mark at 32°F in the 1991–2020 normals. Hold tender transplants until the risk has passed, then plant out.
When is the first fall frost in Ottumwa, IA?
Expect Ottumwa's first fall frost near October 14 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Ottumwa in?
Ottumwa is in USDA hardiness zone 5b. In zone 5b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Ottumwa?
There are roughly 174 frost-free days in Ottumwa (a moderate growing season), running from the average last frost around April 23 to the first fall frost near October 14.
When should I plant tomatoes in Ottumwa?
In Ottumwa, start tomato seeds indoors around February 26–March 12, then transplant seedlings outdoors around April 30 once the danger of frost has passed.
Never miss a window in Ottumwa
An email when it’s time to start seeds, transplant, and sow — timed to Ottumwa’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Oskaloosa · 35 km
- Pella · 59 km
- Newton · 91 km
- Kirksville · 93 km
- Fort Madison · 101 km
- Coralville · 102 km
- Iowa City · 103 km
- Indianola · 103 km
Frost dates recorded at OTTUMWA INDUSTRIAL AP, 10 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Ottumwa, IA — Frost Dates & Zone 5b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00014950. Retrieved from https://blissgarden.com/iowa/ottumwa.