USDA Hardiness Zone 5b
Frost Dates for 83340 — Ketchum, Idaho
NOAA 1991–2020 normals from Bellevue, ID (5,192 ft), 24 miles southeast.
Updated
In Ketchum, the last spring frost (32°F) is around May 13 in half of years and has passed by June 3 in nine years out of ten. The first fall frost comes around October 2, as early as September 15 one year in ten, leaving a typical freeze-free season of 139 days (NOAA, Bellevue, ID).
- Last spring frost
- May 13
- First fall frost
- October 2
- Growing season
- 139 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 4
- Last snow
- April 19
- Winters with snow
- 100%
- Snow per year
- 102"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Ketchum
Half of springs at Bellevue, ID see their last 32°F night by May 13; only one in ten is past it by April 30, and one in ten still has one after June 3. Planting tender crops after May 19 leaves a 30% risk of a frost on them, after May 25 20%, and after June 3 10%. The 21 days between the even-odds date and the one-in-ten date is wider than at 78% of the 67 Idaho stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by October 2 in half of years, as early as September 15 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 12 days later, around October 14; in spring the one-in-ten date for 28°F is May 11, 23 days before the 32°F one. The freeze-free season lasts 139 days in a typical year, shorter than at 61% of the 67 Idaho stations; it reaches 163 days one year in ten and falls short of 112 one year in ten. On average 154 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 20 days longer, to about June 2, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 16 and March 5.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 15 | May 20 | May 25 | May 30 | Jun 2 | Jun 6 | Jun 11 | Jun 16 | Jun 22 |
| 32°F | Apr 30 | May 3 | May 6 | May 9 | May 13 | May 15 | May 19 | May 25 | Jun 3 |
| 28°F | Apr 12 | Apr 17 | Apr 21 | Apr 25 | Apr 28 | May 1 | May 3 | May 7 | May 11 |
| 24°F | Mar 18 | Mar 25 | Mar 31 | Apr 5 | Apr 9 | Apr 13 | Apr 18 | Apr 23 | Apr 30 |
| 20°F | Mar 2 | Mar 7 | Mar 10 | Mar 14 | Mar 17 | Mar 21 | Mar 27 | Apr 1 | Apr 6 |
| 16°F | Feb 15 | Feb 23 | Feb 28 | Mar 2 | Mar 5 | Mar 7 | Mar 10 | Mar 13 | Mar 21 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 3 | Sep 9 | Sep 12 | Sep 16 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 4 |
| 32°F | Sep 15 | Sep 21 | Sep 25 | Sep 29 | Oct 2 | Oct 5 | Oct 8 | Oct 12 | Oct 17 |
| 28°F | Sep 30 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 21 | Oct 24 | Oct 30 |
| 24°F | Oct 10 | Oct 16 | Oct 19 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 11 |
| 20°F | Oct 20 | Oct 27 | Oct 30 | Nov 2 | Nov 6 | Nov 10 | Nov 14 | Nov 18 | Nov 23 |
| 16°F | Oct 28 | Nov 3 | Nov 8 | Nov 12 | Nov 16 | Nov 19 | Nov 23 | Nov 26 | Dec 1 |
Freeze probabilities 1991–2020 at Bellevue, 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 83340 →Compare Ketchum with another place →
When it snows in Ketchum, Idaho
The first measurable snow (0.1 inch or more) in Ketchum usually arrives around November 4, and the last of the season around April 19. Those are the middle dates across the winters of 1991–2020 at Ketchum Rs, ID, 9.2 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 24 days after the last snow.
Planting calendar for 83340
| When | What to do |
|---|---|
| March 4 – March 18 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 18 – April 1 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 15 – April 29 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 13 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 10 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 18 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 2 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 83340 is 24 miles from Bellevue, ID, which stands at 5,192 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 83333 (Hailey). The 2023 USDA Plant Hardiness Zone Map lists ZIP 83340 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.
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.