Frost dates and when to plant in Washington State

United States

In Washington State the last spring frost comes between 15 March (Tacoma) and 21 April (Spokane) — the median of 2016–2025 in 5 cities. The first autumn frost comes between 15 October (Spokane) and 3 December (Tacoma). The frost-free season lasts 177–263 days. Tomato: plant out into open ground 26 April – 13 August, earliest in Yakima, latest in Tacoma.

Frost dates by city in Washington State

City	Last spring frost	First autumn frost	Frost-free days	Climate zone	Tomato: window
Tacoma	15 March	3 December	263	210–269 frost-free days	10 May – 13 August
Olympia	19 March	15 November	241	210–269 frost-free days	31 May – 26 July
Seattle	20 March	24 November	249	210–269 frost-free days	17 May – 4 August
Yakima	13 April	24 October	194	150–209 frost-free days	26 April – 4 July
Spokane	21 April	15 October	177	150–209 frost-free days	15 May – 25 June

Median of 2016–2025 for the 25 km grid cell of the city: the last day at or below 0 °C in spring and the first in autumn (ERA5 reanalysis via Open-Meteo). In a cold year a frost can come a week or two later — Greenly warns 48 hours ahead.

When to plant in Washington State: windows by crop

The earliest start and the latest end among the cities here, each with its city; every city’s own window is on its page. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

Crop	Planting out or sowing
Tomato	26 April (Yakima) – 13 August (Tacoma)
Cucumber	6 May (Yakima) – 18 September (Tacoma)
Bell Pepper, Eggplant	6 May (Yakima) – 13 August (Tacoma)
Zucchini	6 May (Yakima) – 16 September (Tacoma)
Pumpkin	6 May (Yakima) – 8 August (Tacoma)
Watermelon	6 May (Yakima) – 24 August (Tacoma)
Peas	22 February (Tacoma) – 20 September (Tacoma)
Garlic, Tulip, Daffodil, Crocus, Hyacinth	Autumn planting: 15 September (Spokane) – end of December (Seattle)

Weather by month in Washington State

Across the 5 cities the warmest month is August (average days 25.9 … 34.1 °C) and the coldest February (average nights -4.9 … 2.1 °C). 2 of the 5 cities have months with nights below 0 °C on average; the longest such winter is in Spokane (November–March).

Month	Day, °C	Night, °C	Rain, mm
January	1.6 … 8.1 °C	-5.2 … 2.5 °C	185
February	3.8 … 8.3 °C	-4.9 … 2.1 °C	131
March	9.9 … 12.6 °C	-1.3 … 3.5 °C	118
April	14.3 … 18.3 °C	2.5 … 5.5 °C	93
May	18.5 … 25 °C	7.8 … 9.9 °C	51
June	21.5 … 29.5 °C	10.1 … 13.9 °C	50
July	25.6 … 34.9 °C	12.3 … 17.4 °C	9
August	25.9 … 34.1 °C	13.5 … 16.8 °C	25
September	21.5 … 27.8 °C	10.8 … 12.3 °C	65
October	15.2 … 18.3 °C	3.8 … 8.3 °C	129
November	6.8 … 10.7 °C	-1.1 … 5.3 °C	182
December	1.9 … 7.8 °C	-4.3 … 3 °C	200

Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).

Frost dates and when to plant in Washington State

Frost dates by city in Washington State

When to plant in Washington State: windows by crop

Weather by month in Washington State

What to plant month by month: the Pacific Northwest

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