Growing Degree Days in Idaho
Idaho has accumulated about 2368 GDD so far this year (base 50°F, since January 1), averaged across 2 NOAA USCRN stations. Station totals range from 2295 to 2441 GDD. Through September 30, 2026. That is about even with 2025, when Idaho had banked 2343 GDD by September 30, based on 2 stations with records for both years.
How to Read This Number
Growing degree days count accumulated heat: each day adds the amount its average temperature runs above 50°F, the point where cool-season growth and most pests get going. Turf managers use the running total to time crabgrass pre-emergent, annual bluegrass seedhead suppression, plant growth regulator reapplication, and grub control. Treat it as a timing signal read against a model, not a fixed date. The total here is measured air temperature from NOAA USCRN stations, base 50°F, accumulated from January 1. State the model whenever you compare totals, because a different base or start date is not interchangeable.
USCRN Stations in Idaho (2)
| Station | GDD (base 50°F) | Through |
|---|---|---|
| Murphy 10 W | 2,441 | Sep 30 |
| Arco 17 SW | 2,295 | Sep 30 |
Timing Windows for Idaho
Where Idaho sits against the published turf models. Each model carries its own base temperature and start date, so the accumulation column differs from row to row. A status of “varies by area” means the state’s coldest and warmest stations fall on opposite sides of the window.
| Model | Target | Idaho now | Status |
|---|---|---|---|
| Crabgrass pre-emergent timerbase 32°F, from Feb 15 | 250 to 500 GDD | 5,681 to 6,065 | Passed |
| Crabgrass germination timerbase 50°F, from Feb 15 | 200 to 600 GDD | 2,295 to 2,441 | Passed |
| Spring broadleaf herbicide timerbase 50°F, from Feb 15 | 110 to 150 GDD, 150 to 200 GDD, 200 to 600 GDDby formulation | 2,295 to 2,441 | Passed |
| Japanese beetle adult emergencebase 50°F, from Jan 1 | 1030 to 2150 GDD | 2,295 to 2,441 | Passed |
| Poa annua seedhead suppression (Proxy/Primo)base 32°F, from Feb 15 | 200 to 500 GDD | 5,681 to 6,065 | Passed |
| Poa annua seedhead suppression (Embark)base 22°F, from Feb 15 | 680 to 1050 GDD | 7,887 to 8,321 | Passed |
| Poa annua seedhead flushbase 22°F, from Feb 15 | 1050 to 2900 GDD | 7,887 to 8,321 | Passed |
| Early-season dollar spot DMI applicationbase 50°F, from Feb 15 | 140 to 175 GDD | 2,295 to 2,441 | Passed |
| Growth regulator reapplication intervalbase 32°F, from Feb 15 | 200 GDD | 5,681 to 6,065 | Spacing, not a date |
| Broadleaf weed flowering timingsbase 50°F, from Feb 15 | Reference only | 2,295 to 2,441 | Reference |
| Legacy 50/86 modelbase 50°F / 86°F ceiling, from Feb 15 | Reference only | 2,548 to 2,842 | Reference |
Turf professional models are hidden by default. They cover putting greens and fairways rather than home lawns.
Michigan State ground-truthed these models in the Great Lakes region and does not recommend them for the mid-south transition zone or the South. Outside the Upper Midwest and Northeast, read them as a guide and confirm against local extension guidance.
How Idaho Accumulated This Year
Most recent 14 reporting days
Daily and running totals, averaged across the state's 2 reporting stations. Days a station did not report are left out rather than counted as zero, so the dates can skip.
| Date | Daily | Total (base 50°F) | Total (base 32°F) |
|---|---|---|---|
| Sep 17 | 11.6 | 2,256 | 5,670 |
| Sep 18 | 7.8 | 2,264 | 5,696 |
| Sep 19 | 5.9 | 2,271 | 5,720 |
| Sep 20 | 7.7 | 2,278 | 5,746 |
| Sep 21 | 9.8 | 2,288 | 5,773 |
| Sep 22 | 10 | 2,298 | 5,801 |
| Sep 23 | 9.8 | 2,307 | 5,829 |
| Sep 24 | 14.3 | 2,322 | 5,862 |
| Sep 25 | 12.5 | 2,334 | 5,892 |
| Sep 26 | 1.7 | 2,336 | 5,911 |
| Sep 27 | 6.6 | 2,342 | 5,936 |
| Sep 28 | 8.7 | 2,351 | 5,962 |
| Sep 29 | 7.5 | 2,359 | 5,988 |
| Sep 30 | 9.7 | 2,368 | 6,016 |
Month by month, against last year
GDD earned in each month at base 50°F, this year beside 2025.
| Month | 2026 | 2025 | Base 32°F (2026) |
|---|---|---|---|
| January | 0 | 0 | 50 |
| February | 0 | 1 | 159 |
| March | 67 | 13 | 443 |
| April | 28 | 21 | 377 |
| May | 217 | 200 | 756 |
| June | 351 | 424 | 889 |
| July | 773 | 649 | 1,331 |
| August | 661 | 630 | 1,201 |
| September | 271 | 406 | 810 |
| October | — | 40 | — |
| November | — | 7 | — |
| December | — | 5 | — |
Cities in Idaho (12)
Each city page pairs the current soil temperature from its nearest monitoring station with a local growing-degree-day total where a NOAA USCRN station is close enough to measure one.
Growing Degree Days FAQ for Idaho
How many growing degree days has Idaho accumulated this year?
Idaho has accumulated about 2368 growing degree days (base 50°F, since January 1), averaged across 2 NOAA USCRN stations. Station totals range from 2295 to 2441 GDD. The total climbs through summer and levels off as temperatures fall.
What base temperature and start date are these totals?
These are base 50°F growing degree days accumulated from January 1, the turf-industry convention. Each day adds the amount its average air temperature runs above 50°F, floored at zero. Totals from a different base or start date are not interchangeable, so the model is stated explicitly wherever a number appears.
What are growing degree days used for in lawn care?
Turf managers track the running total to time temperature-driven tasks: crabgrass pre-emergent before germination, annual bluegrass seedhead suppression, plant growth regulator reapplication, and grub control. Growing degree days are a timing signal read against a model, not a fixed calendar date.
How does Idaho compare to last year?
Idaho has banked 2368 GDD (base 50°F) through September 30. That is about even with 2025, when Idaho had banked 2343 GDD by September 30, based on 2 stations with records for both years.
Which growing degree day models does this page track for Idaho?
This page reads Idaho's accumulation against the published turf models, each on its own base temperature and start date: Michigan State's crabgrass pre-emergent timer (250 to 500 GDD base 32°F from February 15) and germination timer (200 to 600 GDD base 50°F), Purdue's spring broadleaf windows by formulation, Iowa State's Japanese beetle emergence range, and the professional models for annual bluegrass seedhead suppression, early-season dollar spot, and growth regulator intervals. A target range means nothing without its base and start date, so both travel with every number.
See growing degree days for every state, read the growing degree days lawn-care guide, or browse the full Idaho soil temperature directory.