Frost dates for Boise
The typical last spring frost in Boise is Apr 24, and the typical first fall frost is Oct 21. These dates come from Boise Air Terminal, and the growing season between them is 179 days.
NCEI U.S. Climate Normals 1991-2020, annual/seasonal (c20230404), USW00024131
This season's measured frost
No freeze has been recorded yet this fall at Boise Air Terminal; the lowest reading since July 1 is 39F on Oct 12, against a typical first frost date of Oct 21.
In 2026, the last spring freeze at Boise Air Terminal was on Apr 17 with a low of 29F, 7 days earlier than the typical date of Apr 24.
Readings come from official daily lows in the daily climate report of the National Weather Service, via the Iowa Environmental Mesonet.
Early, typical and late years for Boise
| Year type | Last spring frost | First fall frost |
|---|---|---|
| Early year (1 in 10) | Apr 4 | Oct 5 |
| Typical year | Apr 24 | Oct 21 |
| Late year (1 in 10) | May 9 | Nov 5 |
For spring, an early year means 1 year in 10 has a last freeze before the early date, and a late year means 1 year in 10 has a last freeze after the late date. For fall, an early year means 1 year in 10 has a first freeze by the early date, and a late year means it holds off past the late date.
The growing season in a typical year is 179 days, with the shortest at 156 days and the longest at 203 days in 1 year in 10.
Frost and freeze thresholds
| Last spring frost | First fall frost | |
|---|---|---|
| Light frost (36F) | May 8 | Oct 8 |
| Freeze (32F) | Apr 24 | Oct 21 |
| Hard freeze (28F) | Apr 2 | Oct 31 |
Clear, calm nights can see frost on plants at a low of 36F. A low of 32F is a freeze, and most tender plants are killed at 28F, a hard freeze.
More weather for Boise
A typical date is the median: half of years have an earlier last spring frost, half a later one. An early year means 1 year in 10, and a late year means 1 year in 10. Dates come from the U.S. Climate Normals for 1991-2020, published by NOAA's National Centers for Environmental Information, using a daily low of 32F or below as a freeze.
The daily climate report is issued by the local National Weather Service forecast office and delivered to this page by the Iowa Environmental Mesonet of Iowa State University. Under 17 U.S.C. 105, no copyright attaches to the government-produced figures on this page, including reports, alerts, station observations, and normals, which were created by the National Weather Service and other NOAA offices. The notice that 17 U.S.C. 403 requires appears in this sentence. It does not imply endorsement by or affiliation with those agencies. See: Data sources and attribution.