Suggesting dates for planting vegetables in western Washington state can only be approximate. Although the short, cool summers and mild, rainy winters blanket the entire area west of the Cascade Mountains, there are variations in climate depending on whether you live along the Pacific Ocean or Puget Sound or whether you live inland or at higher elevations.
Some vegetables take longer to mature than others. To know what vegetables to plant and when, you need to know the weather in your part of western Washington.
The growing season in western Washington ranges from 120 to 180 days. The date of the last spring killing frost ranges from April 15 to June 1. The date of the first fall killing frost varies from Sept. 15 to Nov. 1. The coastal areas have the longest growing season, and elevations above 1,000 feet have the shortest season. Other areas are in between.
To view a climate map of western Washington, go to the Washington State University, Home Gardens reference in the Reference section.
Warm Season and Cool Season Vegetables
Warm season vegetables ordinarily need warm ground for their seeds to germinate. They are susceptible to late spring frosts, and they need sun to prosper. Cool season vegetables can withstand frost and grow well in early spring and in cool weather. In western Washington, gardeners can plant cool season vegetables in the late summer and early fall and extend their harvests into the winter by using cold frames and covering rows of vegetables with plastic.
Early Spring Planting
Plant asparagus, lettuce, onions, peas, radishes and rhubarb around March 10 in most areas of western Washington. If you live above 1,000 feet elevation, this date will be one or two weeks later.
Plant beets, broccoli, cabbage, carrots, cauliflower, celery, Swiss chard, kohlrabi, parsnips, potatoes and turnips about two weeks before the average date of the last killing frost. This date will be about April 1 if you live along the coast, May 1 if you live in the interior and May 15 if you live on the western slopes of the Cascade Mountains. Tomato and pepper plants are usually planted as seedlings grown in greenhouses.
Cool Season Planting
Cool season vegetables are also called fall and winter vegetables. They can be planted earlier in the spring and some will continue growing in the fall and into the winter. Although frosts in western Washington sometimes do occur at altitudes below 1,000 feet, frozen soil can usually be prevented by covering the ground with a light mulch.
Plant beets until Aug. 1 and as late as Sept. 1 if you are interested in only beet greens; the tops will grow, but not the beets.
Plant broccoli, Brussels sprouts, cabbage, collards and kale seeds to mid-July and transplant to mid-August. Broccoli will ordinarily produce until Thanksgiving or even Christmas.
Plant carrots by mid-July for a fall or winter harvest.
Plant pole beans by July 1 for a fall crop. Plant bush beans until late July.
Plant Swiss chard by mid-July for a fall crop. Plant in late August for an early spring crop.