Last spring's pre-emergent window, largest Idaho cities
Each bar runs from the day the soil held 50°F to the day it held 55°F (2026).
- 50°F to 55°F
Every Idaho city
Spring 2026 dates and today's verdict.
| City | Held 50°F (2026) | Held 55°F (2026) | Soil today | Today |
|---|---|---|---|---|
| Boise, ID | Mar 19 | May 2 | 54°F | Season over |
| Nampa, ID | Mar 19 | May 2 | 54°F | Season over |
| Idaho Falls, ID | Mar 20 | May 5 | 45°F | Season over |
| Pocatello, ID | Mar 20 | May 25 | 46°F | Season over |
| Coeur d'Alene, ID | May 3 | May 25 | 48°F | Season over |
| Twin Falls, ID | Mar 19 | May 4 | 49°F | Season over |
| Lewiston, ID | May 2 | May 4 | 50°F | Season over |
| Rexburg, ID | Mar 21 | Jun 16 | 44°F | Season over |
| Conda, ID | Jun 15 | Jun 18 | 41°F | Season over |
Crabgrass seeds start to germinate once the top 2 to 4 inches of soil stay near 55°F for several days. A pre-emergent works as a barrier in the soil, so it has to be down and watered in before that: the usual advice is to apply it while the soil holds 50 to 55°F. The dates here are when the modelled soil began to hold each temperature last spring; this year's window will move with the weather, which is why each city page shows today's reading and the 7-day forecast.
Questions
- When should I put down crabgrass preventer in Idaho?
- When the soil holds 50 to 55°F. Last spring that was around Mar 20 to May 5 across 9 Idaho cities, earlier in the south and in cities.
- Is it too late to apply pre-emergent?
- Once the soil has held 55°F for a week or more, crabgrass is germinating and a pre-emergent will not stop the seedlings already up. Each city page says which side of that line it is on today.
Soil temperature today in Idaho →
Data: Global Forecast System (GFS) 0.25°, soil temperature 0–10 cm (TSOIL) (NOAA National Centers for Environmental Prediction (NCEP)); GeoNames gazetteer (cities15000) (GeoNames).