USDA Hardiness Zone 4b
Frost Dates for 59422 — Choteau, Montana
NOAA 1991–2020 normals from Bynum 4 SSE, MT (4,039 ft), 7 miles northeast.
Updated
In Choteau, the last spring frost (32°F) is around May 16 in half of years and has passed by May 28 in nine years out of ten. The first fall frost comes around September 27, as early as September 16 one year in ten, leaving a typical freeze-free season of 133 days (NOAA, Bynum 4 SSE, MT).
- Last spring frost
- May 16
- First fall frost
- September 27
- Growing season
- 133 days
- Hardiness zone
- 4b
50% probability
50% probability
freeze-free, 50%
-25 to -20°F (-31.7 to -28.9°C) coldest night
- First snow
- October 17
- Last snow
- April 30
- Winters with snow
- 100%
- Snow per year
- 47.5"
median, 1991–2020
median, 1991–2020
26 of 26 observed
NOAA normal
Frost risk by date in Choteau
Half of springs at Bynum 4 SSE, MT see their last 32°F night by May 16; only one in ten is past it by May 2, and one in ten still has one after May 28. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 24 20%, and after May 28 10%. The 12 days between the even-odds date and the one-in-ten date is the narrowest of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 27 in half of years, as early as September 16 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 9 days later, around October 6; in spring the one-in-ten date for 28°F is May 15, 13 days before the 32°F one. The freeze-free season lasts 133 days in a typical year, longer than at 63% of the 68 Montana stations; it reaches 151 days one year in ten and falls short of 115 one year in ten. On average 169 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 15 days longer, to about May 31, and return around September 19. Severe cold of 16°F or below comes every winter, usually between November 3 and April 2.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 19 | May 23 | May 26 | May 29 | May 31 | Jun 3 | Jun 6 | Jun 10 | Jun 17 |
| 32°F | May 2 | May 7 | May 10 | May 13 | May 16 | May 18 | May 21 | May 24 | May 28 |
| 28°F | Apr 20 | Apr 25 | Apr 28 | Apr 30 | May 2 | May 5 | May 8 | May 10 | May 15 |
| 24°F | Apr 6 | Apr 11 | Apr 15 | Apr 19 | Apr 23 | Apr 25 | Apr 29 | Apr 30 | May 4 |
| 20°F | Mar 26 | Apr 1 | Apr 4 | Apr 8 | Apr 11 | Apr 14 | Apr 19 | Apr 23 | Apr 28 |
| 16°F | Mar 13 | Mar 20 | Mar 26 | Mar 30 | Apr 2 | Apr 5 | Apr 8 | Apr 13 | Apr 19 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 10 | Sep 13 | Sep 16 | Sep 19 | Sep 21 | Sep 23 | Sep 26 | Oct 1 |
| 32°F | Sep 16 | Sep 20 | Sep 23 | Sep 25 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 9 |
| 28°F | Sep 24 | Sep 29 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 19 |
| 24°F | Oct 1 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 22 | Oct 26 | Oct 31 |
| 20°F | Oct 6 | Oct 13 | Oct 18 | Oct 22 | Oct 25 | Oct 29 | Nov 1 | Nov 5 | Nov 10 |
| 16°F | Oct 16 | Oct 23 | Oct 27 | Oct 31 | Nov 3 | Nov 6 | Nov 10 | Nov 14 | Nov 20 |
Freeze probabilities 1991–2020 at Bynum 4 SSE, MT, 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 59422 →Compare Choteau with another place →
Compared with the next station
The nearest other station, Fairfield, MT, 23 miles southeast of Choteau, has a last frost 3 days earlier (May 13), the same first-frost date, a season 2 days longer.
When it snows in Choteau, Montana
The first measurable snow (0.1 inch or more) in Choteau usually arrives around October 17, and the last of the season around April 30. Those are the middle dates across the winters of 1991–2020 at Choteau, MT, 7.5 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 16 days after the last snow.
Planting calendar for 59422
| When | What to do |
|---|---|
| March 7 – March 21 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 21 – April 4 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 18 – May 2 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 16 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 5 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 13 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 27 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 59422 is 7 miles from Bynum 4 SSE, MT, which stands at 4,039 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59422 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.
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.