When to plant in Great Falls, MT
USDA Zone 4bGreat Falls, Montana frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
In zone 4b, Great Falls winters are severe; choose cold-hardy perennials and time annuals carefully around the frost dates above.
Frost probability
GREAT FALLS 16ST · 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 Great Falls’s own odds, recorded at GREAT FALLS 16ST.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Jun 1 | May 19 | May 6 | Sep 7 | Sep 21 | Oct 3 |
| 32°F | May 19 | May 6 | Apr 23 | Sep 17 | Oct 1 | Oct 16 |
| 28°F | May 8 | Apr 24 | Apr 7 | Sep 25 | Oct 11 | Oct 29 |
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 Great Falls, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 8 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.
Great Falls planting FAQ
When is the last spring frost in Great Falls, MT?
Great Falls's average last spring frost falls near May 6 — 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 Great Falls, MT?
In Great Falls, the first 32°F freeze of fall lands around October 1 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Great Falls in?
Great Falls is in USDA hardiness zone 4b. In zone 4b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Great Falls?
Great Falls has about 148 frost-free days — a short growing season — between the average last spring frost (May 6) and first fall frost (October 1).
When should I plant tomatoes in Great Falls?
For Great Falls, sow tomatoes indoors about March 11–March 25 and move the seedlings out around May 13, after the last spring frost.
Never miss a window in Great Falls
An email when it’s time to start seeds, transplant, and sow — timed to Great Falls’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reachFrost dates recorded at GREAT FALLS 16ST, 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 Great Falls, MT — Frost Dates & Zone 4b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00243749. Retrieved from https://blissgarden.com/montana/great-falls.