Washington is divided into two climate areas by the Cascade Mountains. On the west side the winters are mild, in USDA zones 7 or 8, and the summers are cool. On the east side, winters are colder, in USDA zones 5 and 6, and summers are hot, with temperatures often rising into the high 90s or low 100s. The types of vegetables that do well differ with the climate, and the strategies for planting are different, as well.
Lettuce, spinach, kale, swiss chard, mustard and other greens all do well in cool spring weather and may be direct-seeded in western Washington or overwintered under cold frames. Be sure to raise the pH of the usually acid soil to neutral, especially for spinach.
If you live east of the mountains, you may do better with plants started indoors so you can take advantage of the cool interval between the last frost and the summer heat. Also look for heat-resistant varieties of these plants and give them some shade during the hottest weather. Because you're looking for big leaves, not flowers, they usually tolerate shade well and reward you with fine growth.
The Cabbage Family
These plants, the broccoli, cauliflower, Brussels sprouts and Chinese cabbage group, do well in the mild climate west of the mountains without special treatment. You may direct-seed them or start them indoors before the last frost date. Inland gardeners should use transplants to get them started before the warm weather hits, and look for especially heat-resistant varieties.
Potatos need acid soil, so do a pH test if you live east of the mountains, and add sulfur to acidify the soil if needed.
Onions, carrots, parsnips and beets are all adaptable plants that thrive on both sides of the mountains. Check with your extension service for recommended planting dates.
Peas And Beans
Peas are cool-weather vegetables, planted in February in western Washington and giving a good crop over a long period of time. Plant them as early as possible in eastern Washington, and mulch the soil to keep it cool.
Beans, on the other hand, like warm weather, and do well east of the mountains, though good crops are possible on the west side. Try some of the more cold-tolerant, purple-podded varieties there.
Tomatos, Peppers and Eggplants
These are all heat lovers, ideal for inland gardeners. Just about any variety will grow well for you, though they may need some covering in spring to protect them from cool nights; allow early planting for the best harvest.
West-coast gardeners need to look for quick-ripening varieties and give them as much protection as possible to help them grow and ripen early. Even so, they're a bit of a gamble. In cool summers, they simply may not thrive.
Melons, Cucumbers and Squash
These are ideal for inland gardens. Direct-seed them in warm soil for best results, as they don't transplant well.
Zucchini are reliable in coastal gardens, but look for quick-ripening varieties of cucumbers and winter squash. Melons are usually a poor bet, but if you get a hot summer, you might harvest enough to make them worthwhile. Give them protection as long as possible.
Short-season varieties may succeed in the western part of the state, but inland gardeners have no limitations here. Wait until the soil warms thoroughly before you plant, though, or the seed may rot.