LawnWeather

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

Crabgrass preventer (pre-emergent)
May 7 – Jun 6
Spring fertilizer
May 30 – Jul 4
Overseeding & seeding
Jul 20 – Sep 8
Fall fertilizer
Jul 16 – Oct 13
Light band: typical frost-free season. Bars: typical windows.
TaskTypical 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

  1. JanuaryNo treatments due; mow as needed.
  2. FebruaryNo treatments due; mow as needed.
  3. MarchNo treatments due; mow as needed.
  4. AprilNo treatments due; mow as needed.
  5. MayCrabgrass preventer (pre-emergent)Spring fertilizer
  6. JuneCrabgrass preventer (pre-emergent)Spring fertilizer
  7. JulySpring fertilizerOverseeding & seedingFall fertilizer
  8. AugustOverseeding & seedingFall fertilizer
  9. SeptemberOverseeding & seedingFall fertilizer
  10. OctoberFall fertilizer
  11. NovemberNo treatments due; mow as needed.
  12. 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.

JanFebMarAprMayJunJulAugSepOctNovDec
23°F22°F33°F41°F50°F60°F68°F68°F59°F45°F34°F27°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.

YearCrabgrass window openedLast spring frostFirst fall frost
2025May 9May 7Oct 6
2024May 12May 21Oct 4
2023May 1Apr 29Oct 24
2022May 26May 23Oct 24
2021May 15May 23Sep 17
2020Apr 28May 10Sep 9
2019May 13May 4Sep 29
2018May 5Apr 27Sep 30
2017May 5May 8Sep 24
2016May 4May 12Oct 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

Growing vegetables too? See the Helena planting calendarfor when to start seeds and plant outside.

More Montana lawn calendars

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