When to plant in Helena, MT
USDA Zone 5aEverything below — frost dates, hardiness zone, and what to plant when in Helena, Montana — is derived from the closest NOAA station with complete climate normals.
Zone 5a means Helena sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
The average first fall frost in Helena is now 5 days later than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
HELENA RGNL AP · 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 Helena’s own odds, recorded at HELENA RGNL AP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Jun 13 | May 25 | May 10 | Sep 4 | Sep 19 | Oct 1 |
| 32°F | May 25 | May 9 | Apr 29 | Sep 17 | Sep 30 | Oct 11 |
| 28°F | May 11 | Apr 29 | Apr 15 | Sep 25 | Oct 7 | Oct 22 |
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 Helena, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 25 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.
Helena planting FAQ
When is the last spring frost in Helena, MT?
On average, the last spring frost in Helena is around May 9 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Helena, MT?
In Helena, the first 32°F freeze of fall lands around September 30 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Helena in?
Helena is in USDA hardiness zone 5a. In zone 5a, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Helena?
There are roughly 144 frost-free days in Helena (a short growing season), running from the average last frost around May 9 to the first fall frost near September 30.
When should I plant tomatoes in Helena?
In Helena, start tomato seeds indoors around March 14–March 28, then transplant seedlings outdoors around May 16 once the danger of frost has passed.
Never miss a window in Helena
An email when it’s time to start seeds, transplant, and sow — timed to Helena’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Butte-Silver Bow · 92 km
- Belgrade · 111 km
- Great Falls · 115 km
- Bozeman · 126 km
- Missoula · 156 km
- Kalispell · 250 km
- Billings · 281 km
- Rexburg · 309 km
Frost dates recorded at HELENA RGNL AP, 4 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 Helena, MT — Frost Dates & Zone 5a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00024144. Retrieved from https://blissgarden.com/montana/helena.