USDA Hardiness Zone 8b
Frost Dates for 97360 — Mill City, Oregon
NOAA 1991–2020 normals from Detroit Dam, OR (1,220 ft), 11 miles east.
Updated
In Mill City, the last spring frost (32°F) is around March 9 in half of years and has passed by April 8 in nine years out of ten. The first fall frost comes around December 3, as early as November 8 one year in ten, leaving a typical freeze-free season of 270 days (NOAA, Detroit Dam, OR).
- Last spring frost
- March 9
- First fall frost
- December 3
- Growing season
- 270 days
- Hardiness zone
- 8b
50% probability
50% probability
freeze-free, 50%
15 to 20°F (-9.4 to -6.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 19%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
5 of 27 observed
NOAA normal
Frost risk by date in Mill City
Half of springs at Detroit Dam, OR see their last 32°F night by March 9; only one in ten is past it by February 2, and one in ten still has one after April 8. Planting tender crops after March 23 leaves a 30% risk of a frost on them, after March 31 20%, and after April 8 10%. The 30 days between the even-odds date and the one-in-ten date is wider than at 87% of the 103 Oregon 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 December 3 in half of years, as early as November 8 one year in ten, and holds off past January 4 one year in ten. A hard freeze of 28°F follows 23 days later, around December 26; in spring the one-in-ten date for 28°F is March 8, 31 days before the 32°F one. The freeze-free season lasts 270 days in a typical year, longer than at 92% of the 103 Oregon stations; it reaches 311 days one year in ten and falls short of 227 one year in ten. On average 46 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 39 days longer, to about April 17, and return around November 11. Nights of 24°F, cold enough to damage hardier plants, come in 54% of winters and 16°F in 6%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 26 | Apr 2 | Apr 8 | Apr 12 | Apr 17 | Apr 22 | Apr 29 | May 4 | May 12 |
| 32°F | Feb 2 | Feb 16 | Feb 24 | Mar 3 | Mar 9 | Mar 15 | Mar 23 | Mar 31 | Apr 8 |
| 28°F84% of yrs | Dec 23 | Jan 7 | Jan 18 | Jan 29 | Feb 5 | Feb 14 | Feb 20 | Feb 28 | Mar 8 |
| 24°F54% of yrs | Dec 10 | Dec 23 | Jan 1 | Jan 7 | Jan 16 | Jan 29 | Feb 7 | Feb 16 | Feb 24 |
| 20°F27% of yrs | too rare for a date | ||||||||
| 16°F6% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 25 | Oct 30 | Nov 4 | Nov 7 | Nov 11 | Nov 15 | Nov 19 | Nov 25 | Dec 2 |
| 32°F | Nov 8 | Nov 15 | Nov 22 | Nov 28 | Dec 3 | Dec 8 | Dec 15 | Dec 24 | Jan 4 |
| 28°F84% of yrs | Nov 22 | Dec 1 | Dec 8 | Dec 18 | Dec 26 | Jan 2 | Jan 9 | Jan 20 | Feb 5 |
| 24°F54% of yrs | Dec 1 | Dec 9 | Dec 19 | Dec 27 | Jan 1 | Jan 8 | Jan 18 | Feb 1 | Feb 16 |
| 20°F27% of yrs | too rare for a date | ||||||||
| 16°F6% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Detroit Dam, OR, 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 97360 →Compare Mill City with another place →
Weather by month in Mill City
August is the warmest month at Detroit Dam, OR, averaging 81°F by day and 56°F at night; January is the coldest at 43°F and 36°F. From May to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 78% of years and March still brings one in 55% of years and April still brings one in 17% of years.
Warmth for growing adds up to 2,304 growing degree days a year (base 50°F), more than at 56% of the 103 Oregon stations. 27% of them (616) have built up by the end of June, and August adds the most, 573. Precipitation totals 93.5 inches a year, most in December (15.4") and least in July (0.7"); May to September bring 15% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 43 | 36 | 13.1 | 83% | 12 | 0 |
| Feb | 47 | 37 | 10.0 | 78% | 10 | 2 |
| Mar | 52 | 38 | 10.7 | 55% | 7 | 15 |
| Apr | 57 | 41 | 8.6 | 17% | 3 | 66 |
| May | 65 | 46 | 6.0 | 3% | <1 | 202 |
| Jun | 71 | 51 | 3.8 | 0% | 0 | 331 |
| Jul | 80 | 56 | 0.7 | 0% | 0 | 556 |
| Aug | 81 | 56 | 0.9 | 0% | 0 | 573 |
| Sep | 74 | 53 | 2.8 | 0% | 0 | 404 |
| Oct | 61 | 47 | 8.0 | 6% | <1 | 140 |
| Nov | 49 | 40 | 13.5 | 42% | 5 | 13 |
| Dec | 43 | 37 | 15.4 | 80% | 10 | 1 |
Monthly normals 1991–2020 at Detroit Dam, OR (1,220 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, Silver Creek Falls, OR, 12 miles northwest of Mill City, has a last frost 52 days later (April 30), a first frost 42 days earlier (October 22), a season 96 days shorter.
When it snows in Mill City, Oregon
Measurable snow is rare here: only 5 of 27 winters from 1991 to 2020 recorded 0.1 inch or more at Stayton, OR, 16.8 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 97360
| When | What to do |
|---|---|
| December 29 – January 12 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| January 12 – January 26 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| February 9 – February 23 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| March 9 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 10 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 19 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 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 97360 is 11 miles from Detroit Dam, OR, which stands at 1,220 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97360 in zone 8b, the band where the coldest night of the year averaged 15 to 20°F (-9.4 to -6.7°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.