USDA Hardiness Zone 5b

Frost Dates for 83221 — Blackfoot, Idaho

NOAA 1991–2020 normals from Blackfoot Fire Dept, ID (4,499 ft), 3 miles southeast.

Updated October 28, 2026

In Blackfoot, the last spring frost (32°F) is around May 5 in half of years and has passed by May 22 in nine years out of ten. The first fall frost comes around October 3, as early as September 16 one year in ten, leaving a typical freeze-free season of 149 days (NOAA, Blackfoot Fire Dept, ID).

Last spring frost: May 5
First fall frost: October 3
Growing season: 149 days
Hardiness zone: 5b

First snow: November 17
Last snow: March 12
Winters with snow: 96%
Snow per year: 14.7"

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Frost risk by date in Blackfoot

Half of springs at Blackfoot Fire Dept, ID see their last 32°F night by May 5; only one in ten is past it by April 23, and one in ten still has one after May 22. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 15 20%, and after May 22 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 67 Idaho stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 3 in half of years, as early as September 16 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 13 days later, around October 16; in spring the one-in-ten date for 28°F is May 4, 18 days before the 32°F one. The freeze-free season lasts 149 days in a typical year, longer than at 51% of the 67 Idaho stations; it reaches 169 days one year in ten and falls short of 125 one year in ten. On average 162 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 18 days longer, to about May 23, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 17 and March 4.

Spring: the chance of another night this cold after the date
Low	90%	80%	70%	60%	50%	40%	30%	20%	10%
36°F	May 8	May 12	May 16	May 19	May 23	May 27	Jun 2	Jun 6	Jun 14
32°F	Apr 23	Apr 28	Apr 30	May 3	May 5	May 8	May 11	May 15	May 22
28°F	Apr 6	Apr 12	Apr 15	Apr 19	Apr 22	Apr 25	Apr 28	Apr 30	May 4
24°F	Mar 15	Mar 23	Mar 30	Apr 2	Apr 5	Apr 8	Apr 12	Apr 16	Apr 21
20°F	Feb 28	Mar 5	Mar 9	Mar 12	Mar 16	Mar 22	Mar 27	Apr 1	Apr 6
16°F	Feb 16	Feb 22	Feb 27	Mar 1	Mar 4	Mar 6	Mar 10	Mar 14	Mar 23

Fall: the chance the first night this cold has come by the date
Low	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Sep 4	Sep 10	Sep 14	Sep 18	Sep 21	Sep 24	Sep 28	Oct 1	Oct 5
32°F	Sep 16	Sep 23	Sep 28	Oct 1	Oct 3	Oct 6	Oct 9	Oct 13	Oct 18
28°F	Sep 30	Oct 5	Oct 9	Oct 13	Oct 16	Oct 19	Oct 22	Oct 24	Oct 31
24°F	Oct 13	Oct 18	Oct 21	Oct 24	Oct 27	Oct 30	Nov 1	Nov 5	Nov 11
20°F	Oct 22	Oct 27	Oct 31	Nov 2	Nov 6	Nov 10	Nov 13	Nov 18	Nov 23
16°F	Oct 30	Nov 4	Nov 10	Nov 13	Nov 17	Nov 20	Nov 24	Nov 27	Dec 1

Freeze probabilities 1991–2020 at Blackfoot Fire Dept, ID, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.

Frost risk on any date in 83221 →Compare Blackfoot with another place →

Frost risk through the year in Blackfoot

Frost curve for Blackfoot, Idaho (Blackfoot Fire Dept, ID, NOAA 1991–2020): the chance of another 32°F night falls from 90% on April 23 to 50% on May 5 and 10% on May 22; the chance that the first fall one has come rises from 10% on September 16 to 50% on October 3 and 90% on October 18. — In Blackfoot, the spring curve drops under 10% on May 22 and the fall curve passes 10% on September 16, 117 days later; that gap is longer than at 52% of the 67 Idaho stations with frost dates. The spring risk falls from 90% to 10% over 29 days (April 23 to May 22) and the fall risk climbs from 10% to 90% over 32 days (September 16 to October 18): both ends of the season vary about as much. At Fort Hall 1 NNE, ID, 12 miles south, the same gap runs from June 12 to September 1, 36 days shorter.

Chance of a frost after each planting date in Blackfoot
Planted on	Another 32°F night	28°F night
Apr 21	over 90%	53%
Apr 28	80%	30%
May 550% date	50%	under 10%
May 12	28%	under 10%
May 19	14%	under 10%
May 26	under 10%	under 10%

Weather by month in Blackfoot

July is the warmest month at Blackfoot Fire Dept, ID, averaging 87°F by day and 56°F at night; January is the coldest at 31°F and 17°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 68% of years.

Warmth for growing adds up to 2,337 growing degree days a year (base 50°F), more than at 57% of the 67 Idaho stations. 28% of them (646) have built up by the end of June, and July adds the most, 665. Precipitation totals 12.1 inches a year, most in May (1.8") and least in July (0.5"); May to September bring 40% of it.

Monthly normals 1991–2020 at Blackfoot Fire Dept, ID
Month	High °F	Low °F	Precip. in	32°F night	Nights ≤ 32°F	GDD 50°F
Jan	31	17	1.0	100%	30	0
Feb	37	21	0.7	100%	26	0
Mar	49	29	1.1	100%	22	7
Apr	57	35	1.4	100%	13	43
May	68	43	1.8	68%	3	195
Jun	77	50	1.0	4%	<1	401
Jul	87	56	0.5	0%	0	665
Aug	86	54	0.6	1%	<1	622
Sep	75	46	1.0	38%	1	329
Oct	61	35	1.1	99%	13	71
Nov	45	26	0.8	100%	25	4
Dec	32	18	1.1	100%	29	0

Monthly normals 1991–2020 at Blackfoot Fire Dept, ID (4,499 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.

Compared with the next station

The nearest other station, Fort Hall 1 NNE, ID, 12 miles south of Blackfoot, has a last frost 15 days later (May 20), a first frost 13 days earlier (September 20), a season 30 days shorter.

Frost dates for 83202 (Chubbuck) →

When it snows in Blackfoot, Idaho

The first measurable snow (0.1 inch or more) in Blackfoot usually arrives around November 17, and the last of the season around March 12. Those are the middle dates across the winters of 1991–2020 at Blackfoot Fire Dept, ID, 2.8 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 54 days after the last snow.

Planting calendar for 83221

What to do and when, from the 50% frost dates for Blackfoot, Idaho
When	What to do
February 24 – March 10	Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out.
March 10 – March 24	Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early.
April 7 – April 21	Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil.
May 5 onward	Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast.
by July 11	Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops.
by September 19	Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation.
October 3 onward	Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter.

The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.

Where these figures come from

ZIP 83221 is 3 miles from Blackfoot Fire Dept, ID, which stands at 4,499 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83221 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.

Frost dates across Idaho →

Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.

Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.