What to do in Idaho Falls now
Idaho Falls is in cool-season grass country. Dates are typical for this spot, worked out from 23 years of weather at Idaho Falls Faa Ap; each status uses this year's soil estimates.
Cool-season: tall fescue, Kentucky bluegrass, perennial ryegrass, fine fescue
- Crabgrass pre-emergent Closed May 13 Typical: May 1 – May 182-inch soil held 55°F for a week from May 13, so crabgrass was sprouting. Next window: about May 1 – May 18, 2027.
- Seed or overseed Too late this fall Typical: Aug 21 – Oct 84-inch soil fell below 50°F on Oct 20; new seedlings rarely establish now. Seed next fall from about Aug 21, or dormant-seed once soil is near freezing so seed sprouts in spring.
- Late-fall feeding Last call · about 11 days Typical: Oct 14 – Nov 14Top growth has slowed but roots keep feeding until 4-inch soil cools to about 40°F, typically Nov 14. A final nitrogen feeding now goes to the roots.
Warm-season: bermudagrass, zoysia, St. Augustine, centipede, bahia
- Crabgrass pre-emergent Closed May 13 Typical: May 1 – May 182-inch soil held 55°F for a week from May 13, so crabgrass was sprouting. Next window: about May 1 – May 18, 2027.
- Seed or sod Wait for late spring Typical: Jun 22 – Aug 21Warm-season seed needs 4-inch soil at 65°F or more, and seedlings need the rest of summer to establish. Next window opens about Jun 22.
- Fall pre-emergent (Poa annua) Germinating since Sep 3 Typical: By Aug 164-inch soil fell below 70°F on Sep 3, when annual bluegrass begins to sprout. A pre-emergent now only stops later flushes; plan to apply by about Aug 16 next year.
- Dormancy and last feeding Dormant since about Oct 15 Typical: Around Oct 84-inch soil has stayed under 55°F since Oct 15, so warm-season grass is going brown. It is too late to fertilize; feed again after spring green-up, once soil holds 65°F (typically Jun 22).
The last 60 days and the week ahead
Idaho Falls soil is 2° warmer than normal for Nov 3, warmer than on 65% of those dates since 2005, and 0° warmer than a year ago.
The green line is our estimate of the daily average soil temperature 2 inches down, driven by temperatures at Idaho Falls Faa Ap, 4.3 km from the city center. The dashed part runs the National Weather Service forecast through the same model. Hover or tap for any day.
2-inch soil, estimated From the NWS forecast Normal Normal range (8 years in 10)
Show the numbers
| Date | 2-inch soil | 4-inch soil | Air high / low | Normal (2 in) |
|---|---|---|---|---|
| Oct 20 | 50° | 51° | 69° / 38° | 47° |
| Oct 21 | 52° | 53° | 69° / 44° | 47° |
| Oct 22 | 53° | 53° | 69° / 40° | 46° |
| Oct 23 | 50° | 52° | 52° / 37° | 46° |
| Oct 24 | 47° | 49° | 50° / 30° | 45° |
| Oct 25 | 46° | 48° | 56° / 29° | 44° |
| Oct 26 | 46° | 48° | 60° / 30° | 44° |
| Oct 27 | 44° | 46° | 46° / 32° | 43° |
| Oct 28 | 42° | 45° | 50° / 29° | 42° |
| Oct 29 | 42° | 44° | 54° / 26° | 42° |
| Oct 30 | 43° | 45° | 60° / 33° | 42° |
| Oct 31 | 44° | 45° | 57° / 36° | 41° |
| Nov 1 | 45° | 46° | 49° / 43° | 41° |
| Nov 2 | 44° | 45° | 48° / 36° | 41° |
| Nov 3 | 43° | 45° | 51° / 32° | 41° |
| Nov 4 (forecast) | 42° | 44° | 50° / 30° | 41° |
| Nov 5 (forecast) | 41° | 43° | 48° / 32° | 40° |
| Nov 6 (forecast) | 40° | 42° | 46° / 29° | 40° |
| Nov 7 (forecast) | 40° | 42° | 50° / 31° | 40° |
| Nov 8 (forecast) | 41° | 43° | 56° / 34° | 39° |
| Nov 9 (forecast) | 42° | 44° | 55° / 35° | 39° |
Which grass grows in Idaho Falls
Idaho Falls winters are cold enough (January averages 20°F) that cool-season grasses, mostly Kentucky bluegrass, tall fescue and perennial ryegrass, make up most lawns. They grow in spring and fall and slow down in summer heat.
Idaho Falls soil through the year
Weekly 2-inch estimates for 2026 so far against 2025 and the normal for each week. The red lines mark 50°F, when crabgrass pre-emergent should be down, and 65°F, when warm-season seed sprouts well.
2026 2025 Normal (2005–2025) 8 years in 10
Normal by month
| Month | 2 in | 4 in | Air |
|---|---|---|---|
| Jan | 31° | 32° | 20° |
| Feb | 32° | 33° | 25° |
| Mar | 37° | 38° | 36° |
| Apr | 44° | 45° | 44° |
| May | 54° | 55° | 53° |
| Jun | 63° | 64° | 60° |
| Jul | 71° | 72° | 68° |
| Aug | 69° | 71° | 67° |
| Sep | 61° | 63° | 58° |
| Oct | 48° | 49° | 45° |
| Nov | 37° | 38° | 32° |
| Dec | 32° | 33° | 22° |
Soil: average of our daily estimates, 2005–2025. Air: NOAA 1991–2020 normals for the station.
Typical lawn dates in Idaho Falls
Each date is when the soil estimate (or the air, for freezes) crossed the threshold, year by year since 2005. “Early” and “late” are the 10th and 90th percentile years, so 8 years in 10 fall between them.
| Event | Typical | 2026 |
|---|---|---|
| Last spring freeze (32°F) | May 23 | Jun 11 |
| Crabgrass model: 250 growing degree days | Apr 7 | Mar 12 |
| Pre-emergent window opens (2-inch soil 50°F) | May 1 | Mar 22 |
| Crabgrass begins to sprout (2-inch soil 55°F) | May 18 | May 13 |
| Cool-season lawns start growing (4-inch soil 55°F) | May 17 | May 13 |
| Warm-season seeding opens (4-inch soil 65°F) | Jun 22 | Jun 22 |
| Cool-season seeding opens (4-inch soil under 70°F) | Aug 21 | Sep 4 |
| Cool-season seeding ends (4-inch soil under 55°F) | Oct 8 | Oct 15 |
| Warm-season grass goes dormant (4-inch under 55°F) | Oct 8 | Oct 15 |
| First fall freeze (32°F) | Sep 29 | Sep 15 |
| Roots stop feeding (4-inch soil under 40°F) | Nov 14 | not yet |
Where these numbers come from
There is no soil sensor in most cities, so we estimate it. Shallow soil follows air temperature with a lag of a few days, and runs a little warmer than the air in fall. We fitted that relationship to 190 USDA soil-sensor stations; on years held out of the fit, the estimate was off by 3.3°F on an average day, and it put the spring 55°F date within a median of 3 days. Read the methodology.
Weather: RCC ACIS station KIDA (IDAHO FALLS FAA AP), daily data since 1948. Forecast: National Weather Service, PIH office, issued Nov 4, 2026, 6:31 AM EST. Last observed day: Nov 3, 2026.
Idaho Falls questions
What is the soil temperature in Idaho Falls today? Our estimate for Nov 3 is 43°F at 2 inches and 45°F at 4 inches, as a daily average. Early-morning soil runs a few degrees cooler than that, and afternoon soil warmer.
When should I put down crabgrass pre-emergent in Idaho Falls? Apply when 2-inch soil holds about 50°F and before it holds 55°F. That has typically been May 1 to May 18 in Idaho Falls. For 2026 the window closed on May 13.
Is it too late to overseed in Idaho Falls? Too late this fall. 4-inch soil fell below 50°F on Oct 20; new seedlings rarely establish now. Seed next fall from about Aug 21, or dormant-seed once soil is near freezing so seed sprouts in spring.
Is it too late to fertilize in Idaho Falls? Last call · about 11 days. Top growth has slowed but roots keep feeding until 4-inch soil cools to about 40°F, typically Nov 14. A final nitrogen feeding now goes to the roots.
When is the last frost in Idaho Falls? The last 32°F night of spring has typically come around May 23, and as late as Jun 18 in 1 year in 10. The first fall freeze typically arrives around Sep 29.
Why 2 inches and 4 inches? Crabgrass and most weed seeds sprout in the top inch or two, so pre-emergent timing follows 2-inch soil. Grass seed and roots respond to the slightly steadier soil at about 4 inches.
How accurate is this? It is a model, not a probe in your yard. Expect about 3–4°F of difference on a given day; shade, slope, mulch and irrigation all move real soil. The dates and trends are more reliable than any single day.