When to plant in Mason City, IA
USDA Zone 5aHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Mason City, Iowa — all computed from Mason City's nearest NOAA weather station.
In zone 5a, Mason City gardeners can grow many hardy perennials, while the last and first frost still dictate the annual vegetable calendar.
The average first fall frost in Mason City is now 5 days later than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
MASON CITY · 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 Mason City’s own odds, recorded at MASON CITY.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 19 | May 7 | Apr 25 | Sep 17 | Sep 30 | Oct 12 |
| 32°F | May 9 | Apr 29 | Apr 14 | Sep 25 | Oct 7 | Oct 21 |
| 28°F | Apr 30 | Apr 18 | Apr 3 | Oct 1 | Oct 18 | Oct 31 |
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 Mason City, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 32 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.
Mason City planting FAQ
When is the last spring frost in Mason City, IA?
Mason City's average last spring frost falls near April 29 — 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 Mason City, IA?
Expect Mason City's first fall frost near October 7 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Mason City in?
Mason City is in USDA hardiness zone 5a. In zone 5a, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Mason City?
Mason City has about 161 frost-free days — a moderate growing season — between the average last spring frost (April 29) and first fall frost (October 7).
When should I plant tomatoes in Mason City?
For Mason City, sow tomatoes indoors about March 4–March 18 and move the seedlings out around May 6, after the last spring frost.
Never miss a window in Mason City
An email when it’s time to start seeds, transplant, and sow — timed to Mason City’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Albert Lea · 58 km
- Austin · 61 km
- Waverly · 76 km
- Cedar Falls · 93 km
- Waterloo · 100 km
- Owatonna · 105 km
- Fort Dodge · 107 km
- Rochester · 113 km
Frost dates recorded at MASON CITY, 2 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 Mason City, IA — Frost Dates & Zone 5a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00135230. Retrieved from https://blissgarden.com/iowa/mason-city.