When is the last frost in Boise, ID?

The average (50% probability) last spring frost in Boise is April 24, based on NOAA 1991–2020 normals. A 1-in-10 risk remains until May 9.

When is the first frost in Boise?

The average first fall frost in Boise is October 21, with a growing season of about 179 days.

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Boise, Idaho frost dates

Average last spring frost: April 24. Average first fall frost: October 21. That gives a growing season of about 179 days. For frost-tender plants, a safer planting date is May 9, after which a freeze happens in only 1 year in 10.

Last frost (50%)

Apr 24

1-in-10 risk after May 9

First frost (50%)

Oct 21

1-in-10 risk before Oct 5

Growing season

179 days

median frost-free days

Hard freeze (28°F)

Apr 2

median last 28°F in spring

Frost risk by date

Chance of frost	Spring: frost after	Fall: frost before
90%	April 4	November 5
70%	April 17	October 27
50%	April 24	October 21
30%	April 30	October 14
10%	May 9	October 5

Read the spring column like this: there is a 10% chance of a 32°F freeze after May 9. These are NOAA probabilities for the Boise Air Terminal weather station (USW00024131, elevation 858 m), 1991–2020.

Boise vegetable planting calendar

Dates count from the 50% last-frost date (April 24). For tomatoes, peppers and other frost-tender crops, waiting until the 10% date (May 9) is the cautious choice.

Crop	Start seeds indoors	Plant out
Beans	Apr 3	May 1 (usually sown directly in the garden)
Broccoli	Feb 13	Mar 27
Brussels sprouts	Feb 13	Mar 27
Cabbage	Feb 6	Mar 20
Cauliflower	Feb 27	Apr 10
Sweet corn	Mar 27	Apr 24 (usually sown directly in the garden)
Cucumbers	Apr 10	May 1
Kale	Feb 6	Mar 20
Leeks	Jan 9	Mar 20
Lettuce	Mar 6	Apr 10
Melons	Apr 17	May 8
Onions	Jan 2	Mar 13 (from seed; sets and transplants go out at the same time)
Peas	Feb 27	Mar 27 (usually sown directly in the garden)
Peppers	Mar 13	May 8
Squash	Apr 17	May 8
Tomatoes	Feb 27	Apr 24

Offsets from Oregon State University Extension's seed-starting table. "Plant out" means transplant, or sow directly for crops usually grown from seed.

Fall frost and season extension

The first fall freeze usually arrives around October 21. There's a 1-in-10 chance it comes before October 5. Harvest tender crops such as basil, tomatoes, peppers and squash before then, or cover them on cold nights. Cool-season crops like kale, cabbage and Brussels sprouts handle light frost, and often taste sweeter after it. A hard freeze (28°F) typically comes around October 31.

Nearby cities

City	Last frost (50%)	First frost (50%)	Distance
Missoula, MT	May 16	Sep 26	~410 km
Spokane, WA	Apr 26	Oct 12	~462 km
Salt Lake City, UT	Apr 8	Oct 31	~462 km
Yakima, WA	May 8	Oct 4	~480 km
Reno, NV	Apr 20	Oct 23	~535 km
Medford, OR	Apr 8	Oct 29	~549 km

More: all Idaho frost dates