Plan your garden spot. Select the sunniest spot in your yard, preferably on a slight slope. A site with southwestern exposure provides the most sunlight.
Scoop soil from different areas of your garden into the soil bags or vials that came with your soil test kit. Mail the soil kit to your extension office. You'll receive the soil test report in two or three weeks. The report offers detailed information about the type of soil you have (clay or sand), the pH level and any nutrient deficiencies. The report also makes recommendations for improving your soil.
Lay 1 to 2 inches of compost on the soil in your garden. Rototill or shovel the compost into your soil and rake until smooth. Add any other amendments recommended by the soil test report.
Consult your local extension office to choose seeds and plants suitable for your area. Cool-weather crops, such as lettuce, broccoli and peas, thrive almost year round in western Washington's mild, moist climate. Choose short-season crops in eastern Washington. These crops mature earlier (within 60 to 90 days), allowing you to harvest a crop before the first frost in the fall.
Plant early spring crops, such as swiss chard, onions and peas, after March 10 in western Washington and after April 10 in eastern Washington. Plant mid-spring crops, such as broccoli, beets and cabbage, two weeks before the last frost. Plant warm-season crops, such as tomatoes, beans and corn, after all danger of frost has passed.
Protect young seedlings with row covers and cloches. Tomatoes and peppers are especially vulnerable to cold night air. Keep them covered until night temperatures are consistently above 60 degrees Fahrenheit. Extend your growing season by planting crops two to three weeks earlier and protecting them (especially important for eastern Washington gardeners).
Water your plants to keep them evenly moist. Water weekly for at least 30 minutes in eastern Washington. Water as needed in western Washington. Check the moisture level in your garden by sticking your finger into the soil. The soil should feel moist 2 to 3 inches below the surface. If it feels dry, you need to water. Adjust your watering schedule for rainy or hot weather.
Apply fertilizer two to three weeks after you planted your garden and when plants are blossoming. Apply fertilizer based on the soil test recommendations. Most western Washington gardens need a complete fertilizer (nitrogen, phosphorus, potassium), while eastern Washington gardens require only nitrogen.
Consult your local county extension office if you notice fungus, black spots, white powder or wilting leaves. Numerous pests and diseases afflict western Washington gardens because of the moist, mild conditions. Identify the problem and follow your extension office expert's advice in treating it.