Gardening in Washington

Hardiness zones in Washington

Washington's USDA hardiness zones run from 6a to 9b. That is one of the widest ranges of any state. A hardiness zone tells you the average annual minimum winter temperature in your area. It does not tell you about summer heat, rainfall, or soil type. Zone 6a areas see colder winter lows, while zone 9b areas stay much milder. The state's full zone list includes 6a, 6b, 7a, 7b, 8a, 8b, 9a, and 9b. This spread reflects the gap between inland highlands and the milder coast and valleys. Use your zone to judge which perennials and woody plants can survive winter outdoors where you garden. A plant rated for zone 7 should handle the winter lows typical of zone 7 areas. Gardeners in zone 6a need to pick tougher, more cold-hardy plants than those in zone 9b. Checking your local zone first narrows your plant choices before you buy anything.

• Zone 6a
• Zone 6b
• Zone 7a
• Zone 7b
• Zone 8a
• Zone 8b
• Zone 9a
• Zone 9b

Frost dates

Frost dates mark when the growing season starts and ends in your area. Across Washington, the earliest last spring frost on record falls on February 26. The latest last spring frost on record falls on June 6. That six-week-plus spread shows how much frost timing varies across the state. In fall, the earliest first frost can arrive as early as September 4 in some spots. Other areas do not see their first fall frost until November 29. These dates come from readings at 149 weather stations across the state. If your last frost date runs late, wait until after it to plant tender crops outdoors. If your first fall frost tends to come early, protect frost-sensitive plants well before that date. Elevation and distance from the coast both push these dates earlier or later than the state average. Check a frost record from a station near you rather than relying on one statewide figure.

Climate

Washington's climate varies widely from one part of the state to another. Hardiness zones across the state span 6a to 9b, a gap of several full zones. That range points to a big difference in winter cold between the coldest and mildest spots. Growing season length tells a similar story. The longest growing season recorded in the state runs 276 days. The shortest growing season recorded runs just 65 days. A gardener with a 276-day season can grow crops that need a long, frost-free stretch. A gardener with a 65-day season must pick fast-maturing crops or start plants indoors first. Frost timing backs this up as well. Last spring frost dates range from February 26 in the mildest areas to June 6 in the coldest. First fall frost dates range from September 4 to November 29. This data comes from 149 weather stations spread across Washington. That many stations capture real differences between coastal areas, lowland valleys, and higher inland ground. Do not treat any single zone or frost date as true for the whole state. Instead, use the figures for the station closest to your own garden. Local terrain and closeness to water shift conditions more than a statewide average can show.

Season length

Growing season length in Washington ranges from 65 days to 276 days depending on where you garden. That is the gap between your last spring frost and your first fall frost. A short 65-day season limits you to quick crops like radishes, lettuce, and bush beans planted directly outdoors. A long 276-day season leaves room for slower crops such as tomatoes, winter squash, and many perennial flowers. Count the days between your area's typical last and first frost dates to estimate your own season length. Then match your plant choices to that number rather than to a statewide average.