Washington State offers a unique challenge for potato growers due to its diverse geography. Successful planting depends entirely on recognizing the climatic differences created by the Cascade Mountain range. The mild, wet conditions of the western side contrast sharply with the arid, continental climate east of the mountains, which directly impacts when the soil is ready to receive seed potatoes. Understanding these regional variations is the first step toward a successful harvest. A grower must look past a simple calendar date and instead focus on environmental readiness to ensure the seed potatoes thrive rather than rot in cold, wet ground.
Timing is Everything: Regional Planting Schedules in Washington
The planting window for potatoes shifts significantly based on which side of the Cascade Mountains a gardener is located. West of the Cascades, a milder maritime climate means gardeners can often begin planting as soon as the soil is workable in early spring. In the Puget Sound area, some growers aim to plant as early as mid-March, provided the soil is not waterlogged and has drained sufficiently from winter rains. The primary concern for Western Washington growers is cold, saturated soil, which can cause the seed potato to rot before it sprouts.
Planting should proceed once the soil temperature consistently reaches at least 45°F, a condition typically met from late March through mid-April in Western Washington. East of the Cascades, the climate is drier, but the risk of hard frost persists later into the spring. This region, encompassing the Columbia Basin, generally requires a later planting schedule to ensure the emerging shoots are safe from freezing temperatures.
Commercial operations in the warmer South Basin of Eastern Washington may begin planting in mid-February, but this relies on sophisticated irrigation and soil management. For the home gardener in Eastern Washington, waiting until mid-April or even early May is a more reliable approach, ensuring the final danger of hard frost has passed. Planting in staggered intervals, a few weeks apart, can help mitigate weather risks and extend the harvest season, regardless of the region.
Preparing for Planting
Before a seed potato ever touches the earth, it requires preparation to ensure a vigorous start. Gardeners should always begin with certified disease-free seed potatoes, avoiding those purchased from grocery stores which may carry pathogens or growth inhibitors.
Chitting and Curing
A week or two before planting, “chitting” can be initiated by placing the seed potatoes in a cool area with indirect light, which encourages short, stubby sprouts to form. This pre-sprouting gives the plant a head start once it is placed in the soil. Larger seed potatoes should be cut into blocky pieces, about 1.5 inches square, ensuring each piece contains at least one or two “eyes.” After cutting, the pieces must be left at room temperature for a few days to “cure,” forming a protective, calloused layer over the cut surface. This cured layer prevents the seed piece from decaying in the cool, moist soil before it can sprout.
Soil Preparation
Soil preparation is equally important, as potatoes thrive in loose, well-draining earth. Ideally, the soil should have a slightly acidic pH between 5.4 and 6.6, which helps deter the common scab disease.
Step-by-Step Planting Guide
The act of planting involves creating a shallow, temporary trench in the prepared soil. Dig a furrow about 6 to 8 inches deep, which will serve as the initial bed for the seed potatoes. Place the prepared seed pieces into the bottom of this trench with the cut side facing down and any visible sprouts pointing upward. Optimal spacing is 10 to 12 inches between each seed piece within the row, with rows separated by 2 to 3 feet to allow for hilling and maintenance.
After placing the seed potatoes, initially cover them with only 3 to 4 inches of soil. The trench should not be completely filled at this stage, as the remaining depth is reserved for the hilling process later on. This shallow initial cover allows the seed piece to warm up and sprout faster. Once planted, avoid watering unless the soil is extremely dry, as excessive moisture can promote rot of the seed piece before the roots develop.
Essential Post-Planting Care and Harvesting
Once the potato plants emerge and reach a height of approximately 6 to 8 inches, the maintenance task of “hilling” must begin. Hilling involves mounding loose soil, compost, or straw around the base of the stems, partially burying the lower third of the plant. This practice serves two main purposes: it protects developing tubers from sunlight, which prevents them from turning green and producing the toxic compound solanine, and it encourages the plant to form more tubers along the buried stem.
Hilling should be repeated every few weeks as the plant grows taller, continuing until the foliage begins to flower or reaches a height that makes further mounding impractical. Throughout the growing season, consistent moisture is necessary, especially after the plants begin to flower, which is when the tubers start to rapidly enlarge. Potatoes require about one to two inches of water per week; uneven watering during this stage can lead to misshapen or cracked tubers.
Harvest timing depends on the desired product. “New potatoes” can be gently dug up shortly after the plants flower. Mature, storage-ready potatoes are harvested later, once the entire plant’s foliage has naturally died back and turned brown. After the foliage dies, waiting an additional 10 to 14 days allows the potato skins to thicken, which improves their storage life.