Helena, MT Lawn Care Calendar
In a typical year, put down crabgrass preventer in Helena between May 7 and Jun 6. The best time to overseed is between Jul 20 and Sep 8. The last spring frost usually comes around May 10. Most lawns here are cool-season grass (tall fescue, Kentucky bluegrass, ryegrass).
Typical lawn care dates in Helena
| Task | Typical window |
|---|---|
| Crabgrass preventer (pre-emergent)Crabgrass sprouts once soil stays above 55°F. Apply when soil reaches 50°F, before that happens. | May 7 – Jun 6 |
| Spring fertilizerA light feeding once soil warms past 55°F and the grass is actively growing. | May 30 – Jul 4 |
| Overseeding & seedingLate summer to early fall: seedlings need about 6–10 weeks of growth before the first frost. | Jul 20 – Sep 8 |
| Fall fertilizerThe most important feeding for cool-season grass, from early fall until soil cools to about 45°F. | Jul 16 – Oct 13 |
Median dates, 2016–2025, from NOAA weather data for Helena. This year's dates can differ by a few weeks.
Month-by-month lawn care in Helena
- JanuaryNo treatments due; mow as needed.
- FebruaryNo treatments due; mow as needed.
- MarchNo treatments due; mow as needed.
- AprilNo treatments due; mow as needed.
- MayCrabgrass preventer (pre-emergent)Spring fertilizer
- JuneCrabgrass preventer (pre-emergent)Spring fertilizer
- JulySpring fertilizerOverseeding & seedingFall fertilizer
- AugustOverseeding & seedingFall fertilizer
- SeptemberOverseeding & seedingFall fertilizer
- OctoberFall fertilizer
- NovemberNo treatments due; mow as needed.
- DecemberNo treatments due; mow as needed.
Soil temperature in Helena by month
Average soil temperature 4 inches down, estimated from 2016–2025 weather. It bottoms out in February at 22°F and peaks in July at 68°F. Crabgrass preventer goes down when it reaches 50°F, usually around May 7.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 23°F | 22°F | 33°F | 41°F | 50°F | 60°F | 68°F | 68°F | 59°F | 45°F | 34°F | 27°F |
Helena lawn timing, year by year
Over the last 10 years, soil in Helena reached 50°F, the signal for crabgrass preventer, as early as Apr 28 (2020) and as late as May 26 (2022): 28 days apart. A fixed calendar date can't follow that, which is why the report above uses this year's soil temperature. Between the typical last spring frost (May 10) and first fall frost (Oct 3), the growing season lasts about 146 days.
| Year | Crabgrass window opened | Last spring frost | First fall frost |
|---|---|---|---|
| 2025 | May 9 | May 7 | Oct 6 |
| 2024 | May 12 | May 21 | Oct 4 |
| 2023 | May 1 | Apr 29 | Oct 24 |
| 2022 | May 26 | May 23 | Oct 24 |
| 2021 | May 15 | May 23 | Sep 17 |
| 2020 | Apr 28 | May 10 | Sep 9 |
| 2019 | May 13 | May 4 | Sep 29 |
| 2018 | May 5 | Apr 27 | Sep 30 |
| 2017 | May 5 | May 8 | Sep 24 |
| 2016 | May 4 | May 12 | Oct 7 |
Estimated from daily temperatures for Helena. A dash means it didn't happen that year.
Frequently asked questions
When should I apply pre-emergent in Helena?
In a typical year, between May 7 and Jun 6. Put it down when soil reaches 50°F, before it stays above 55°F and crabgrass starts sprouting. Early springs move this up by a week or more, so check this year's soil temperature above.
When is the best time to plant grass seed in Helena?
Early fall, typically Jul 20 – Sep 8, while soil cools from 65°F toward 50°F.
When is the last frost in Helena?
The median last spring frost is May 10 and the median first fall frost is Oct 3 (2016–2025).
How long is the growing season in Helena?
About 146 days, from the median last spring frost on May 10 to the median first fall frost on Oct 3 (2016–2025).
Lawn care guides
More Montana lawn calendars
Nearby cities in other states
- Idaho Falls, ID 214 miles away · crabgrass preventer May 3 – Jun 6
- Coeur d'Alene, ID 235 miles away · crabgrass preventer Apr 27 – May 18
- Pocatello, ID 258 miles away · crabgrass preventer Apr 29 – May 22
- Spokane, WA 264 miles away · crabgrass preventer Apr 26 – May 15