Missoula, Montana: planting zone & frost dates
Missoula is in USDA plant hardiness zone 5b, where the average coldest winter night reaches -15 to -10°F (-26.1 to -23.3°C). The typical last spring frost is around May 22 and the first fall frost around Sep 20.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Jun 1 | Sep 12 |
| Typical planning date (30% risk) | May 22 | Sep 20 |
| Median (50%) | May 16 | Sep 26 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station MISSOULA INTL AP, MT (USW00024153), 4.5 mi (7.2 km) from the city center and 23 ft higher than the city center (+7 m). Record used for the 1991–2020 normals: 21 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Missoula
All 6 ZIP codes covering Missoula are in zone 5b.
Vegetable planting calendar for Missoula
Dates are counted from the 30%-risk frost dates above (last frost May 22, first frost Sep 20). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 27 – Apr 10 | May 29 – Jun 12 | — | — |
| Pepper | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Lettuce | Apr 10 – Apr 24 | May 8 – May 29 | Apr 24 – Jun 5 | Jul 12 – Aug 9 |
| Green Beans | — | — | May 29 – Jul 3 | Jun 28 – Jul 12 |
| Sweet Corn | — | — | May 29 – Jun 26 | — |
| Zucchini & Summer Squash | Apr 24 – May 1 | May 29 – Jun 12 | May 29 – Jun 19 | Jun 28 – Jul 12 |
| Cucumber | Apr 24 – May 1 | Jun 5 – Jun 12 | May 29 – Jun 19 | Jun 28 – Jul 12 |
| Carrot | — | — | May 1 – Jun 5 | Jun 28 – Jul 12 |
| Onion | Feb 27 – Mar 13 | Apr 24 – May 8 | — | — |
| Potato | — | Apr 24 – May 15 | — | — |
| Basil | Apr 10 – Apr 24 | Jun 5 – Jun 19 | Jun 5 – Jun 26 | — |
| Spinach | — | — | Apr 10 – May 8 | Jul 26 – Aug 23 |
| Kale | Mar 27 – Apr 10 | Apr 24 – May 15 | Apr 24 – May 15 | Jul 12 – Aug 9 |
| Broccoli | Mar 27 – Apr 10 | May 8 – May 29 | — | Jun 28 – Jul 12 |
| Peas | — | — | Apr 10 – May 1 | Jul 12 – Jul 26 |
| Eggplant | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Cabbage | Mar 27 – Apr 10 | Apr 24 – May 8 | — | Jun 28 – Jul 12 |
| Radish | — | — | Apr 17 – Jun 5 | Aug 9 – Sep 6 |
| Strawberry | — | Apr 24 – May 15 | — | — |
| Beets | — | — | May 1 – Jun 12 | Jul 12 – Jul 26 |
Nearby cities in Montana
- Billings — zone 5a, last frost May 11, first frost Sep 28
More: all Montana cities · other zone 5b cities: Madison, WI, Des Moines, IA, Aurora, IL, Fort Collins, CO, Naperville, IL, Rockford, IL, Elgin, IL, Greeley, CO
Missoula gardening questions
When is the last frost in Missoula, MT?
Plan around May 22. At NOAA's Missoula Int'l Airport, MT station, 4.5 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by May 16, and after Jun 1 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around May 2. The 90% and 10% dates are 29 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Missoula, MT?
Start seeds indoors Mar 27 – Apr 10 and set transplants outside May 29 – Jun 12, once nights stay above 50°F and the soil is near 60°F. That leaves 121 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Missoula?
About 130 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 107 days, and in 1 year in 10 it runs 149 days or more. In fall there is a 10% chance of frost by Sep 12 and a 30% chance by Sep 20.
When should I plant a fall garden in Missoula?
Count back from the first fall frost (Sep 20): transplant broccoli Jun 28 – Jul 12; sow kale Jul 12 – Aug 9; sow lettuce Jul 12 – Aug 9; sow radishes Aug 9 – Sep 6. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 6. How the math works: succession and fall planting.
Did Missoula's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Missoula is zone 5b on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.