Frost Dates for Mason City, IA
In Mason City, IA, the average last spring frost is around Apr 29 and the average first fall frost around Oct 7, for a growing season of about 161 days. For frost-tender plants, wait until May 9, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Mason City, IA weather station, 1 mile away, elevation 1,105 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 9 | Sep 25 |
| 20% | May 6 | Sep 29 |
| 30% | May 3 | Oct 1 |
| 40% | Apr 30 | Oct 4 |
| 50% | Apr 29 | Oct 7 |
| 60% | Apr 25 | Oct 10 |
| 70% | Apr 22 | Oct 13 |
| 80% | Apr 19 | Oct 17 |
| 90% | Apr 14 | Oct 21 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | May 7 | Sep 30 |
| Frost / freeze (32°F) | Apr 29 | Oct 7 |
| Hard freeze (28°F) | Apr 18 | Oct 18 |
Planting calendar for Mason City
Transplant May 6 – May 20
Transplant May 13 – May 27
Transplant May 13 – May 27
Transplant May 6 – May 20
Sow or transplant May 6 – May 20
Sow or transplant May 6 – May 20
Sow or transplant May 13 – May 27
Sow or transplant Apr 1 – Apr 15
Fall sowing Aug 12 – Sep 9
Fall sowing Aug 12 – Sep 2
Fall sowing Jul 29 – Aug 12
Sow or transplant Apr 1 – Apr 15
Fall sowing Jul 29 – Aug 26
Transplant Apr 15 – Apr 29
Fall sowing Jul 15 – Jul 29
Transplant Apr 8 – Apr 22
Fall sowing Jul 15 – Jul 29
Fall sowing Jul 15 – Jul 29
Fall sowing Aug 26 – Sep 16
Fall sowing Jul 29 – Aug 12
Plant Apr 1 – Apr 15
Based on the average last frost (Apr 29) and first frost (Oct 7). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.