USDA Hardiness Zone 7a
Frost Dates for 99324 — College Place, Washington
NOAA 1991–2020 normals from Whitman Mission, WA (632 ft), 4 miles west.
Updated
In College Place, the last spring frost (32°F) is around May 2 in half of years and has passed by May 18 in nine years out of ten. The first fall frost comes around October 1, as early as September 14 one year in ten, leaving a typical freeze-free season of 151 days (NOAA, Whitman Mission, WA).
- Last spring frost
- May 2
- First fall frost
- October 1
- Growing season
- 151 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- December 11
- Last snow
- February 10
- Winters with snow
- 95%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
19 of 20 observed
NOAA normal
Frost risk by date in College Place
Half of springs at Whitman Mission, WA see their last 32°F night by May 2; only one in ten is past it by April 16, and one in ten still has one after May 18. Planting tender crops after May 8 leaves a 30% risk of a frost on them, after May 13 20%, and after May 18 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 74% of the 113 Washington stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 1 in half of years, as early as September 14 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 11 days later, around October 12; in spring the one-in-ten date for 28°F is May 1, 17 days before the 32°F one. The freeze-free season lasts 151 days in a typical year, shorter than at 86% of the 113 Washington stations; it reaches 172 days one year in ten and falls short of 128 one year in ten. On average 125 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 16 days longer, to about May 18, and return around September 17. Severe cold of 16°F or below comes in 96% of winters, usually between December 2 and February 7.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 3 | May 7 | May 11 | May 15 | May 18 | May 21 | May 25 | May 31 | Jun 7 |
| 32°F | Apr 16 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 5 | May 8 | May 13 | May 18 |
| 28°F | Mar 23 | Mar 31 | Apr 5 | Apr 10 | Apr 15 | Apr 19 | Apr 23 | Apr 27 | May 1 |
| 24°F | Feb 28 | Mar 5 | Mar 10 | Mar 15 | Mar 20 | Mar 27 | Apr 1 | Apr 7 | Apr 16 |
| 20°F | Jan 23 | Feb 7 | Feb 17 | Feb 24 | Feb 28 | Mar 2 | Mar 7 | Mar 13 | Mar 24 |
| 16°F96% of yrs | Dec 28 | Jan 10 | Jan 23 | Feb 1 | Feb 7 | Feb 15 | Feb 23 | Feb 28 | Mar 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 1 | Sep 5 | Sep 10 | Sep 14 | Sep 17 | Sep 21 | Sep 24 | Sep 28 | Oct 2 |
| 32°F | Sep 14 | Sep 20 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 10 | Oct 16 |
| 28°F | Sep 28 | Oct 2 | Oct 5 | Oct 8 | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 30 |
| 24°F | Oct 7 | Oct 13 | Oct 19 | Oct 24 | Oct 27 | Nov 1 | Nov 5 | Nov 12 | Nov 23 |
| 20°F | Oct 21 | Oct 29 | Nov 2 | Nov 8 | Nov 13 | Nov 21 | Nov 27 | Dec 5 | Dec 17 |
| 16°F96% of yrs | Nov 1 | Nov 11 | Nov 19 | Nov 26 | Dec 2 | Dec 8 | Dec 16 | Dec 29 | Jan 10 |
Freeze probabilities 1991–2020 at Whitman Mission, WA, 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 99324 →Compare College Place with another place →
Weather by month in College Place
July is the warmest month at Whitman Mission, WA, averaging 90°F by day and 54°F at night; December is the coldest at 41°F and 27°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 55% of years.
Warmth for growing adds up to 2,616 growing degree days a year (base 50°F), more than at 80% of the 113 Washington stations. 31% of them (815) have built up by the end of June, and July adds the most, 682. Precipitation totals 15.4 inches a year, most in May (1.8") and least in July (0.4"); May to September bring 29% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 42 | 27 | 1.7 | 100% | 23 | 3 |
| Feb | 48 | 28 | 1.4 | 100% | 20 | 4 |
| Mar | 57 | 32 | 1.7 | 100% | 16 | 21 |
| Apr | 65 | 37 | 1.5 | 99% | 8 | 79 |
| May | 73 | 44 | 1.8 | 55% | 2 | 269 |
| Jun | 80 | 49 | 1.1 | 0% | 0 | 440 |
| Jul | 90 | 54 | 0.4 | 0% | 0 | 682 |
| Aug | 90 | 52 | 0.4 | 1% | 0 | 642 |
| Sep | 80 | 44 | 0.7 | 46% | 1 | 361 |
| Oct | 66 | 36 | 1.3 | 99% | 13 | 97 |
| Nov | 50 | 31 | 1.7 | 100% | 18 | 16 |
| Dec | 41 | 27 | 1.7 | 100% | 24 | 4 |
Monthly normals 1991–2020 at Whitman Mission, WA (632 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, Walla Walla Regional Airport, WA, 6 miles northeast of College Place and 534 feet higher, has a last frost 36 days earlier (March 27), a first frost 30 days later (October 31), a season 68 days longer.
When it snows in College Place, Washington
The first measurable snow (0.1 inch or more) in College Place usually arrives around December 11, and the last of the season around February 10. Those are the middle dates across the winters of 1991–2020 at Whitman Mission, WA, 3.7 miles away: half of years saw snow earlier, half later. Snow fell in 95% of those winters. The last 32°F night of spring typically comes 81 days after the last snow.
Planting calendar for 99324
| When | What to do |
|---|---|
| February 21 – March 7 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 7 – March 21 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 4 – April 18 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 2 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 17 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 1 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 99324 is 4 miles from Whitman Mission, WA, which stands at 632 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99324 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across Washington →
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.