Boulder, CO Lawn Care Calendar
In a typical year, put down crabgrass preventer in Boulder between Apr 13 and May 17. The best time to overseed is between Aug 3 and Sep 22. The last spring frost usually comes around Apr 25. Most lawns here are cool-season grass (tall fescue, Kentucky bluegrass, ryegrass).
Typical lawn care dates in Boulder
| Task | Typical window |
|---|---|
| Crabgrass preventer (pre-emergent)Crabgrass sprouts once soil stays above 55°F. Apply when soil reaches 50°F, before that happens. | Apr 13 – May 17 |
| Spring fertilizerA light feeding once soil warms past 55°F and the grass is actively growing. | May 10 – Jun 14 |
| Overseeding & seedingLate summer to early fall: seedlings need about 6–10 weeks of growth before the first frost. | Aug 3 – Sep 22 |
| Fall fertilizerThe most important feeding for cool-season grass, from early fall until soil cools to about 45°F. | Sep 4 – Nov 5 |
Median dates, 2016–2025, from NOAA weather data for Boulder. This year's dates can differ by a few weeks.
Month-by-month lawn care in Boulder
- JanuaryNo treatments due; mow as needed.
- FebruaryNo treatments due; mow as needed.
- MarchNo treatments due; mow as needed.
- AprilCrabgrass preventer (pre-emergent)
- MayCrabgrass preventer (pre-emergent)Spring fertilizer
- JuneSpring fertilizer
- JulyNo treatments due; mow as needed.
- AugustOverseeding & seeding
- SeptemberOverseeding & seedingFall fertilizer
- OctoberFall fertilizer
- NovemberFall fertilizer
- DecemberNo treatments due; mow as needed.
Soil temperature in Boulder by month
Average soil temperature 4 inches down, estimated from 2016–2025 weather. It bottoms out in January at 32°F and peaks in July at 74°F. Crabgrass preventer goes down when it reaches 50°F, usually around Apr 13.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 32°F | 33°F | 41°F | 47°F | 56°F | 68°F | 74°F | 73°F | 67°F | 53°F | 43°F | 36°F |
Boulder lawn timing, year by year
Over the last 10 years, soil in Boulder reached 50°F, the signal for crabgrass preventer, as early as Mar 16 (2017) and as late as Apr 29 (2018): 44 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 (Apr 25) and first fall frost (Oct 17), the growing season lasts about 175 days.
| Year | Crabgrass window opened | Last spring frost | First fall frost |
|---|---|---|---|
| 2025 | Mar 26 | Apr 21 | Oct 19 |
| 2024 | Apr 13 | Apr 22 | Oct 31 |
| 2023 | Apr 11 | Apr 24 | Oct 27 |
| 2022 | Apr 21 | May 22 | Oct 25 |
| 2021 | Apr 4 | Apr 23 | Oct 15 |
| 2020 | Apr 24 | Apr 19 | Sep 9 |
| 2019 | Apr 20 | May 22 | Oct 10 |
| 2018 | Apr 29 | Apr 26 | Oct 10 |
| 2017 | Mar 16 | May 20 | Oct 9 |
| 2016 | Apr 5 | May 3 | Oct 20 |
Estimated from daily temperatures for Boulder. A dash means it didn't happen that year.
Frequently asked questions
When should I apply pre-emergent in Boulder?
In a typical year, between Apr 13 and May 17. 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 Boulder?
Early fall, typically Aug 3 – Sep 22, while soil cools from 65°F toward 50°F.
When is the last frost in Boulder?
The median last spring frost is Apr 25 and the median first fall frost is Oct 17 (2016–2025).
How long is the growing season in Boulder?
About 175 days, from the median last spring frost on Apr 25 to the median first fall frost on Oct 17 (2016–2025).
Lawn care guides
More Colorado lawn calendars
Nearby cities in other states
- Cheyenne, WY 82 miles away · crabgrass preventer May 12 – Jun 8
- Laramie, WY 91 miles away · crabgrass preventer May 20 – Jun 11
- Casper, WY 205 miles away · crabgrass preventer May 12 – May 29
- North Platte, NE 248 miles away · crabgrass preventer Apr 24 – May 14