Although potatoes (Solanum tuberosum) are popularly associated with Idaho, the tubers are especially well suited to Washington, and large amounts are grown commercially in the Columbia Basin. The details of planting for the home gardener are not substantially different than for other states, but planting dates may vary, and some areas of the state are better suited for growing potatoes than others.
Climate and Soil Preparation
Potatoes in Washington are best planted between the middle of April and the beginning of August for harvest between the beginning August to the beginning of November. They take from 90 to 120 days to mature.
As a cool-season crop, potatoes are especially well suited to the interior valley west of the Cascade Mountains, along the Columbia River east of Vancouver, the Yakima Valley and the Columbia Basin.
You can plant potatoes up to two weeks before the last expected frost in your area, but the soil temperature should be at least 45 degrees Fahrenheit when you plant them.
Till the soil 8 to 12 inches deep one week before you plant the potatoes. At the same time, apply 2 to 3 pounds of 10-10-10 water-soluble fertilizer per 100 square feet. Apply it 6 to 7 inches deep and 2 to 3 inches to the side of the row where you will plant the potatoes. Water well after adding the fertilizer.
Obtaining Seed Potatoes
Potato plants grow from buds found in dimples, called eyes, on the outside of pieces cut from seed potatoes. Don’t try to use grocery store potatoes as seed potatoes. They may carry diseases, and many are treated with chemicals to prevent them from sprouting. Buy seed potatoes certified to be disease-free from a nursery or garden-supply center.
Each seed potato will yield several seed pieces with eyes. Ten plants will yield about 20 pounds of potatoes. The average adult eats about 70 pounds of potatoes a year.
If you’re a gardener in Washington, russets, the large baking potato, are inexpensive and widely available in grocery stores. If you want a potato treat, try one of these varieties:
- ‘Yukon Gold,’ a high-yield potato with yellow flesh that's good for mashing, roasting and baking takes from 70 to 85 days to mature.
- ‘All Blue,’ a high-yield, long potato with dark blue-purple skin and flesh, is good for salads and baking. It takes 85 to 100 days to mature.
- ‘Red LaSoda,’ widely grown by home gardeners, is a high-yield oval potato with light red skin and white flesh that can be baked or boiled and used in salads. ‘Red LaSoda’ takes more than 100 days to mature.
Cutting Seed Potatoes
Use a sterilized knife to cut seed potatoes into chunks each containing an eye. These seed pieces should be 2 to 2 1/2 ounce each or about 1 to 2 inches wide. One pound of potatoes should give you six to eight seed pieces.
Leave the cut seed pieces in a dark, well-ventilated place at 60 to 65 degrees Fahrenheit for one or two days so the wounds can heel.
To sterilize your knife, soak it for five minutes in a solution of 1 part rubbing alcohol to 1 part of water, then let it air-dry.
Planting the Potatoes
You’ll need about 12 pounds of seed pieces for a row 100 feet long.
Plant potato eyes with the cut side down and the eye facing up 2 to 3 inches deep and 12 inches apart in rows spaces 30 to 36 inches apart.
Use a hoe to pull a ridge of soil over the seed pieces after you finish planting them and water well. Keep them evenly moist through the growing season.