Frost Dates   (Data source WSU AgWeatherNet)
Station Avg Last Frost Date (Temp) Avg First Frost Date (Temp)
Mount Vernon March 24 (31°F) October 30 (30°F)
Fir Island March 8 (30°F) October 29 (31°F)

Find your Frost Dates in Washington state.


2021 Annual Rainfall

Note: A new weather station for Mount Vernon was installed in July 2020 so Average Cumulative Precipitation is not available for the full year.



Growing Degree Data

Seed and Plant Selection

Before choosing vegetables for your garden, you want to make sure that your plant is appropriate for the Pacific Northwest.  Our short summers make certain crops unrealistic for most gardeners.  It is essential to consider if the crop you plant will have the opportunity to mature.

Days to Harvest/Days to Maturity
Days to harvest is roughly how long before you can expect ripe fruit.  Days to maturity can also be a guide to distinguish varieties as early (65 days or less), mid-season (65 to 80 days) and late-season (80 days or more).   For the Pacific Northwest, gardeners should mostly look at early varieties unless they have a greenhouse.

Growing Days
All days are not created equal for growing plants.   Your goal in starting plants indoors is to maximize the available growing season.  Growing Degree Days (GDD) are days that meet or exceed a base temperature where the plants receive adequate warmth for tissue growth.  Base temperatures vary by crop type.  Wheat requires less warmth to grow than a tomato.  The base temperature for warm season crops such as tomatoes and peppers is 50 °F.  GDD is calculated by subtracting the base temperature (50 °F in this case) from the average daily temperature (add the high and the low temperature for the day and divide by two).  If the resulting value is less than 0, then it is set to 0.  GDD units are always positive.  If it is above 50, it is a GDD.  If a tomato variety lists 60 days to harvest, you will need 60 GDD for that plant to produce ripe fruit.  Regional GDD data is maintained for growers to estimate when to plant based on historical averages.  Learn more about Growing Days from WSU