When is the last frost in Idaho City, ID?

For ZIP code 83631, the average last spring frost (32°F) is June 17, based on NOAA 1991-2020 climate normals for the Idaho City, ID weather station. There is a 1-in-10 chance of a frost after July 4.

When is the first frost in Idaho City, ID?

The average first fall frost (32°F) is September 5. There is a 1-in-10 chance of frost by August 23, so tender plants are at risk from that point on.

How long is the growing season in 83631?

In half of years, the frost-free season (between the last and first 32°F frost) is at least 80 days long.

Are these frost dates a forecast?

No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.

Frost dates for 83631Idaho City, ID

The average last spring frost in Idaho City is June 17 and the average first fall frost is September 5, giving a typical growing season of about 80 days. Dates are based on NOAA 1991-2020 climate normals.

Average last spring frost: Jun 17
Average first fall frost: Sep 5
Growing season: 80 days

Frost risk by date

NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.

Spring dates: chance of a frost AFTER the date. Fall dates: chance of a frost BEFORE the date.
Temperature	Last spring: 90% / 50% / 10% chance	First fall: 10% / 50% / 90% chance	Growing season (50%)	Years with at least one
Light frost (36°F)	—	—	52 days	100%
Frost / freeze (32°F)	May 30 · Jun 17 · Jul 4	Aug 23 · Sep 5 · Sep 21	80 days	100%
Hard freeze (28°F)	May 7 · May 22 · Jun 14	Sep 3 · Sep 19 · Oct 5	117 days	100%

Where these dates come from

ZIP code 83631 is matched to the NOAA station Idaho City, ID, 11.1 km away, at 3,965 ft elevation (1,511 ft lower than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Idaho City, ID (used)	3,965 ft	Jun 17	Sep 5
Lowman, ID	3,920 ft	Jun 6	Sep 4
Garden Valley, ID	3,100 ft	Jun 1	Sep 10
Arrowrock Dam, ID	3,235 ft	Apr 28	Oct 14

Frost dates near Idaho City

Placerville, ID 83666 · last Jun 17, first Sep 5
Garden Valley, ID 83622 · last Jun 17, first Sep 5
Lowman, ID 83637 · last —, first —
Atlanta, ID 83601 · last Jun 16, first Sep 6
Horseshoe Bend, ID 83629 · last Apr 30, first Oct 17
Banks, ID 83602 · last Jun 1, first Sep 10
Boise, ID 83716 · last May 17, first Oct 12
Garden City, ID 83714 · last Apr 24, first Oct 21

Frequently asked questions

When is the last frost in Idaho City, ID?: For ZIP code 83631, the average last spring frost (32°F) is June 17, based on NOAA 1991-2020 climate normals for the Idaho City, ID weather station. There is a 1-in-10 chance of a frost after July 4.
When is the first frost in Idaho City, ID?: The average first fall frost (32°F) is September 5. There is a 1-in-10 chance of frost by August 23, so tender plants are at risk from that point on.
How long is the growing season in 83631?: In half of years, the frost-free season (between the last and first 32°F frost) is at least 80 days long.
Are these frost dates a forecast?: No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.