When Is the Last Frost in Montana?
The average last spring frost in Montana falls between May 9 and June 6 for most ZIP codes, with a statewide median of May 20. At the average date a later frost is still a coin flip, so tender plants wait for the safer 90% date.
| City | Last frost | 90% safe after | First frost | Growing season |
|---|---|---|---|---|
| Billings | May 5 | May 21 | Oct 3 | 149 days |
| Missoula | May 10 | May 28 | Oct 1 | 143 days |
| Great Falls | May 6 | May 19 | Oct 1 | 147 days |
| Bozeman | May 23 | Jun 12 | Sep 23 | 123 days |
| Butte | Jun 13 | Jul 1 | Sep 5 | 83 days |
| Helena | May 9 | May 25 | Sep 30 | 142 days |
| Kalispell | May 31 | Jun 22 | Sep 10 | 100 days |
| Belgrade | May 26 | Jun 12 | Sep 15 | 111 days |
| Anaconda | Jun 1 | Jun 25 | Sep 14 | 105 days |
| Whitefish | May 16 | Jun 6 | Sep 25 | 129 days |
| Havre | May 15 | May 27 | Sep 23 | 129 days |
| Livingston | May 19 | Jun 11 | Sep 25 | 125 days |
| Miles City | May 8 | May 21 | Sep 30 | 144 days |
| Lewistown | May 14 | May 27 | Sep 28 | 135 days |
| Sidney | May 11 | May 25 | Sep 27 | 137 days |
| Polson | May 10 | May 26 | Oct 5 | 147 days |
| Hamilton | May 21 | Jun 6 | Sep 22 | 122 days |
| Glendive | May 3 | May 16 | Oct 4 | 153 days |
Last and first frost: 50% (median) dates of the last spring and first fall 32 °F night. 90% safe after: only a 10% chance of a later spring frost. First frost dates in January fall in the following winter. Each city uses the NOAA station nearest the ZIP code closest to its center.
Across all 216 Montana weather stations with frost records, median last frost dates run from April 30 at Norris Madison Pwr House, MT to June 18 at Tizer Gardens, MT. Elevation, valleys that collect cold air and distance from large water bodies explain most of the spread, so a garden a few miles from a listed city can differ by a week or more. The ZIP code lookup above uses the same NOAA data as the frost date calculator for every US ZIP code.
When Is the First Frost in Montana?
The average first fall frost in Montana arrives between September 8 and October 1 for most ZIP codes, with a median of September 22. Tomatoes, peppers, basil and squash are damaged at 32 °F, so harvest or cover them before then.
Fall frost can come early: Billings has a 10% chance of frost before September 20, Missoula has a 10% chance of frost before September 16 and Great Falls has a 10% chance of frost before September 17. Hardy crops such as kale, spinach and cabbage tolerate light frosts and keep producing after the first frost date.
When to Plant Tomatoes in Montana?
Transplant tomatoes in Montana 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 12 – May 19 in Billings, May 17 – May 24 in Missoula and May 13 – May 20 in Great Falls. Start seeds indoors 6 to 8 weeks before the last frost.
| City | Start seeds indoors | Transplant outdoors | Lowest-risk transplant |
|---|---|---|---|
| Billings | Mar 10 – Mar 24 | May 12 – May 19 | after May 21 |
| Missoula | Mar 15 – Mar 29 | May 17 – May 24 | after May 28 |
| Great Falls | Mar 11 – Mar 25 | May 13 – May 20 | after May 19 |
| Bozeman | Mar 28 – Apr 11 | May 30 – Jun 6 | after Jun 12 |
| Butte | Apr 18 – May 2 | Jun 20 – Jun 27 | after Jul 1 |
| Helena | Mar 14 – Mar 28 | May 16 – May 23 | after May 25 |
| Kalispell | Apr 5 – Apr 19 | Jun 7 – Jun 14 | after Jun 22 |
| Belgrade | Mar 31 – Apr 14 | Jun 2 – Jun 9 | after Jun 12 |
| Anaconda | Apr 6 – Apr 20 | Jun 8 – Jun 15 | after Jun 25 |
| Whitefish | Mar 21 – Apr 4 | May 23 – May 30 | after Jun 6 |
| Havre | Mar 20 – Apr 3 | May 22 – May 29 | after May 27 |
| Livingston | Mar 24 – Apr 7 | May 26 – Jun 2 | after Jun 11 |
| Miles City | Mar 13 – Mar 27 | May 15 – May 22 | after May 21 |
| Lewistown | Mar 19 – Apr 2 | May 21 – May 28 | after May 27 |
| Sidney | Mar 16 – Mar 30 | May 18 – May 25 | after May 25 |
| Polson | Mar 15 – Mar 29 | May 17 – May 24 | after May 26 |
| Hamilton | Mar 26 – Apr 9 | May 28 – Jun 4 | after Jun 6 |
| Glendive | Mar 8 – Mar 22 | May 10 – May 17 | after May 16 |
Indoors: 6–8 weeks before the average last frost. Outdoors: 1–2 weeks after it. Lowest-risk: after the date with only a 10% chance of a later frost. Rules of thumb; check the 10-day forecast and wait for soil near 60 °F.
Tomatoes stall below about 50 °F at night and are killed by frost, so a week or two of waiting after the average date costs little. The tomato plant care guide covers light, watering and feeding once plants are in the ground. With a median growing season of only 122 days, early-maturing varieties, black plastic mulch or a greenhouse help tomatoes ripen before the first fall frost.
What Can You Plant in Billings and When?
Billings's average last frost of May 5 anchors its spring planting calendar: peas and spinach go in from March 24, broccoli and lettuce transplants from April 7, and tomatoes, peppers and squash after May 12.
| Crop | Start seeds indoors | Plant outdoors | Frost tolerance |
|---|---|---|---|
| Peas | — | Mar 24 – Apr 7direct sow, 4–6 weeks before last frost | hardy |
| Spinach | — | Mar 24 – Apr 14direct sow, 3–6 weeks before last frost | hardy |
| Radishes | — | Mar 31 – Apr 14direct sow, 3–5 weeks before last frost | hardy |
| Onions (sets) | — | Apr 7 – Apr 21plant, 2–4 weeks before last frost | hardy |
| Potatoes | — | Apr 7 – Apr 21plant, 2–4 weeks before last frost | half-hardy |
| Broccoli & cabbage | Mar 10 – Mar 24 | Apr 7 – Apr 21transplant, 2–4 weeks before last frost | hardy |
| Lettuce | Mar 24 – Apr 7 | Apr 7 – Apr 21transplant, 2–4 weeks before last frost | hardy |
| Beets | — | Apr 7 – Apr 21direct sow, 2–4 weeks before last frost | half-hardy |
| Carrots | — | Apr 14 – Apr 21direct sow, 2–3 weeks before last frost | half-hardy |
| Tomatoes | Mar 10 – Mar 24 | May 12 – May 19transplant, 1–2 weeks after last frost | tender |
| Basil | Mar 10 – Mar 24 | May 12 – May 26transplant, 1–3 weeks after last frost | tender |
| Peppers | Feb 24 – Mar 10 | May 19 – May 26transplant, 2–3 weeks after last frost | tender |
| Eggplant | Feb 24 – Mar 10 | May 19 – May 26transplant, 2–3 weeks after last frost | tender |
| Green beans | — | May 12 – May 26direct sow, 1–3 weeks after last frost | tender |
| Sweet corn | — | May 12 – May 26direct sow, 1–3 weeks after last frost | tender |
| Cucumbers | Apr 7 – Apr 14 | May 12 – May 26transplant, 1–3 weeks after last frost | tender |
| Squash & zucchini | Apr 7 – Apr 14 | May 12 – May 26transplant, 1–3 weeks after last frost | tender |
| Watermelon | Apr 7 – Apr 14 | May 19 – May 26transplant, 2–3 weeks after last frost | tender |
Dates for Billings (last frost May 5, NOAA station Billings WFO, MT, 2 miles from ZIP 59102). General rules of thumb; wait for soil near 50 °F for most seeds and 60 °F for beans, corn and squash.
How Long Is the Growing Season in Montana?
The frost-free growing season in Montana lasts about 92 to 143 days for most ZIP codes, with a median of 122 days. Among the listed cities, Butte has the shortest season at 83 days and Glendive the longest at 153.
Season length decides which varieties ripen: compare it with the “days to maturity” on seed packets, counted from transplanting for tomatoes and peppers. NOAA stations in Montana range from 77 days at Lewistown 42 WSW, MT to 165 days at Bigfork 13 S, MT. Planning beds before the season starts helps in short seasons — a plant spacing calculator for vegetable beds shows how many transplants fit.
What Hardiness Zones Are in Montana?
Montana spans USDA hardiness zones 3b to 6b, with zone 4b the most common. Zones describe winter cold and decide which perennials survive, while frost dates set when to plant annual vegetables and flowers.
The Montana planting zone map with the zone of each city shows how the zones are spread across the state and which plants are hardy in all of them.
Frequently Asked Questions
- When is the last frost in Montana?
- The average last spring frost in Montana falls between May 9 and June 6 for most ZIP codes, with a statewide median of May 20. Among major cities it ranges from May 3 in Glendive to June 13 in Butte.
- When is the last frost in Billings, Montana?
- Billings's average last spring frost is May 5, and by May 21 the chance of a later frost drops to 10%. Its first fall frost averages October 3, giving a 149-day growing season (NOAA station Billings WFO, MT).
- When should you plant tomatoes in Montana?
- Transplant tomatoes in Montana 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 12 – May 19 in Billings, May 17 – May 24 in Missoula and May 13 – May 20 in Great Falls. Start seeds indoors 6 to 8 weeks before the last frost.
- When is the first frost in Montana?
- The average first fall frost in Montana arrives between September 8 and October 1 for most ZIP codes, with a median of September 22. Harvest tender crops such as tomatoes, peppers and basil before then or cover them on cold nights.
- How long is the growing season in Montana?
- The frost-free growing season in Montana lasts about 92 to 143 days for most ZIP codes, with a median of 122 days, from 83 days in Butte to 153 days in Glendive.
Frost data: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals (32 °F freeze dates by probability). ZIP code and city locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. Planting windows are general rules of thumb. PlantoScan is not affiliated with or endorsed by these agencies.