Washington Frost Dates & Growing Season Guide
Washington (WA) spans USDA hardiness zones 6a, 8a, 8b, with growing seasons ranging from 156 days in Spokane to 255 days in Seattle. The average growing season across the state is approximately 219 days.
Washington City Frost Dates
The table below shows the average last spring frost date, first fall frost date, growing season length, and USDA hardiness zone for each city. Click a city name for detailed planting calendars and zone information.
Planting Windows for Washington
Based on average frost dates, here are the recommended planting windows for each city. The indoor seed start date is approximately seven weeks before the last spring frost. Transplanting should occur about two weeks after the last frost. The last direct sow date for fall crops is ten weeks before the first fall frost.
Gardening in Washington
Washington State's climate split by the Cascade Range creates two distinct gardening worlds. Western Washington around Seattle and Tacoma in zone 8b enjoys mild, wet winters and cool summers with 245 to 255 frost-free days but relatively low summer heat. Eastern Washington around Spokane has a continental climate with hot summers, cold winters, and about 156 frost-free days. Western Washington excels at cool-season crops, berries, and greens, while eastern Washington's hot days and irrigated conditions produce excellent melons, peppers, and stone fruits. Slug management dominates western garden challenges, while water access defines eastern possibilities. Raised beds and season extension are popular statewide.
Understanding Washington's Hardiness Zones
Washington includes USDA hardiness zones 6a, 8a, 8b. These zones indicate the average annual extreme minimum winter temperature for each area, which determines which perennial plants, trees, and shrubs can survive winter without protection. When purchasing trees, shrubs, or perennial flowers, always check that the plant is rated for your hardiness zone or a lower (colder) zone number.
Tips for Using Washington Frost Dates
These frost dates represent long-term averages and should be treated as guidelines rather than guarantees. In any given year, the actual last spring frost or first fall frost may arrive one to three weeks earlier or later than the average. Factors that affect your specific location include elevation above the city center, proximity to water, slope direction, and whether you are in an urban or rural area. South-facing slopes and areas near large pavement or building masses tend to be warmer than surrounding open land. Low-lying valleys and exposed hilltops are often colder than mid-slope positions.
To protect against late spring frosts, keep row cover fabric, old bed sheets, or frost blankets on hand. Monitor your local weather forecast daily as the average frost date approaches. When frost is predicted after you have transplanted, covering plants in the late afternoon traps ground heat and can protect against temperatures down to about 28 degrees Fahrenheit. For fall season extension, the same covers protect mature plants from early frosts, often buying several additional weeks of harvest.