
Sunset climate zones: Western Washington
To see a larger zone map, click the link under image.
ZONE 1A: Coldest mountain and intermountain areas of the contiguous states
Marked by a short growing season and relatively mild summer temperatures, Zone 1A includes the coldest regions west of the Rockies, excluding Alaska, and a few patches of cold country east of the Great Divide. The mild days and chilly nights during the growing season extend the bloom of summer perennials like columbines and Shasta daisies. If your garden gets reliable snow cover (which insulates plants), you’ll be able to grow perennials listed for some of the milder zones. In years when snow comes late or leaves early, protect plants with a 5- or 6-inch layer of organic mulch. Along with hardy evergreen conifers, tough deciduous trees and shrubs form the garden’s backbone. Gardeners can plant warm-season vegetables as long as they are short-season varieties. To further assure success, grow vegetables from seedlings you start yourself or buy from a nursery or garden center. Winter lows average in the 0 to 11°F (–18 to –12°C) range; extremes range from –25 to –50°F (–32 to –46°C). The growing season is 50 to 100 days.
ZONE 4: Cold-winter areas of the north coast and mild-winter areas of Alaska and British Columbia
One of the West’s most narrow, linear climates, Zone 4 runs from high in the coastal mountains of Northern California to southeastern Alaska, losing elevation as it moves north. It gets considerable influence from the Pacific Ocean, but also from the continental air mass, higher elevation, or both. As it extends north, the zone first touches salt water in northern Puget Sound and is almost entirely surrounded by salt water in southeastern Alaska. In the contiguous states, Zone 4 has more cold than neighboring Zone 5,more snow, and a shorter growing season. Compared to neighboring zones in Alaska and Canada, however, it has less winter cold and a longer growing season. No zone grows better perennials and bulbs; people who like woodland plants and rock plants love Zone 4. But beware: though you can grow winter vegetables in the southern part of Zone 4, it doesn’t get enough winter sunlight in Alaska to sustain them. Average winter lows in Zone 4 range from 34°F (1°C) down to 28°F (–2°C),with extreme lows averaging 8 to 0°F (–13 to –18°C). The growing season is 150 to 200 days long, but because Zone 4 summers are temperate (highs average from the low 60s to the 70s), plants take more time to develop. If you’re growing vegetables, for example, add at least 50 percent to the days-to-harvest figure listed on the seed package, or start your garden from transplants.