Mason City, IA planting zone & frost dates
Mason City is in USDA hardiness zone 5a. The last spring frost usually comes around April 29 and the first fall frost around October 7, for a growing season of about 161 days.
Planting calendar for Mason City
Dates are counted from the average last spring frost (April 29) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 4 – Mar 18 Transplant outdoors: May 6 – May 13 |
| Peppers | Start seeds indoors: Feb 18 – Mar 4 Transplant outdoors: May 13 – May 20 |
| Eggplant | Start seeds indoors: Feb 18 – Mar 4 Transplant outdoors: May 13 – May 20 |
| Broccoli | Start seeds indoors: Feb 18 – Mar 4 Transplant outdoors: Apr 1 – Apr 15 |
| Cabbage | Start seeds indoors: Feb 18 – Mar 4 Transplant outdoors: Apr 1 – Apr 15 |
| Onions (sets) | Plant outdoors: Apr 1 – Apr 15 |
| Peas | Sow outdoors: Mar 18 – Apr 1 |
| Spinach | Sow outdoors: Mar 18 – Apr 1 |
| Lettuce | Sow outdoors: Apr 1 – Apr 15 |
| Carrots | Sow outdoors: Apr 1 – Apr 15 |
| Potatoes | Plant outdoors: Apr 1 – Apr 15 |
| Beans | Sow outdoors: May 6 – May 13 |
| Sweet corn | Sow outdoors: May 6 – May 13 |
| Cucumbers | Sow outdoors: May 6 – May 13 |
| Squash & zucchini | Sow outdoors: May 6 – May 13 |
| Basil | Start seeds indoors: Mar 18 – Apr 1 Transplant outdoors: May 6 – May 13 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 12 (8 weeks before the average first fall frost on Oct 7).
Useful for zone 5a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 14 | Apr 29 | May 9 |
| First 32°F frost in fall is before | Oct 21 | Oct 7 | Sep 25 |
How to read it: in spring there is a 10% chance of a frost after May 9, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 25. A hard freeze (28°F) usually ends around April 18.
Hardiness zone by ZIP code in Mason City
- 50401 zone 5a
- 50402 zone 5a
Nearby cities
- Waverly zone 5a, last frost Apr 27
- Cedar Falls zone 5a, last frost Apr 27
- Waterloo zone 5a, last frost Apr 27
- Marshalltown zone 5a, last frost Apr 28
- Fort Dodge zone 5a, last frost Apr 28
- Ames zone 5b, last frost Apr 26
- Boone zone 5a, last frost Apr 28
- Newton zone 5b, last frost Apr 22
Questions
What growing zone is Mason City, IA?
Mason City is in USDA Plant Hardiness Zone 5a (average extreme winter low -20°F to -15°F), according to the USDA 2023 map.
When is the last frost in Mason City?
The average last spring frost (32°F) in Mason City is April 29. There is still a 10% chance of frost until May 9.
When can I plant tomatoes in Mason City?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 6 – May 13. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Mason City, IA (USC00135230), 1.2 km (0.7 mi) from the city center, elevation 337 m, based on 29 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.