Can I grow sweet potatoes in the temperate climate of Washington state?
Answer: You can grow sweet potatoes in more temperate climates with some extra steps and care. PlantingSweet potato slips need to be planted when the weather has stabilized in the late spring. If the soil temperature is at least 55?F to 65?F (there is conflicting information on this, so you might want to be safe and plant in the 60?F range). Territorial Seeds suggests planting the slip upon arrival. If the soil temperature is less than 55?F, plant the slips in four-inch containers and keep in a warm location. At planting time, select an area in the garden that receives full sun and has well drained soil. Rototill or fork in a two-inch thick layer of compost and plenty of bone meal. In shorter-seasoned areas, a raised bed covered with black plastic makes the best planting environment. Rows are usually placed 32 to 42 inches apart with in-row spacing of 12 to 18 inches, depending on the cultivar. Closer spacings delay harvest in most cultivars. Avoid disturbing the roots with foot traffic or deep hoeing. Water thoroughly about every seven to 10 days. If water is provided at transplanting and as necessary for the next 40 days, the plants will probably survive if drought becomes a problem later in the season. Planting the slips in a deep trench and ‘hilling up’ the soil as the plants grow will increase yields dramatically. Be sure to keep at least 12 inches of the plant foliage exposed above the soil as you periodically hill it up. HarvestAfter the weather cools in the fall, carefully loosen the soil around the roots. CuringCuring should be started within one to two hours of harvest and continued for four to seven days at 85?F and 90 to 95 percent relative humidity with periodic venting. In the absence of better facilities, they can be cured near a furnace to provide warmth. If the temperature near your furnace is between 65?F and 75?F, the curing period should last two to three weeks. You may also be able to do this in a greenhouse or sunroom if you have one. To maintain the required high humidity (85 to 90 percent relative humidity), stack storage crates or boxes and cover them with paper or heavy cloth. Packing in perforated plastic bags will also keep humidity high, and the perforations will allow excess moisture to escape.After curing, handle carefully and store them at 50?F to 60?F. For more information on sweet potato production, see the ATTRA publication Sweetpotato: Organic Production at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=32. This publication describes advances in organic sweet potato production?propagation, soil fertility and fertilization, tillage and weed management, insect pest and disease management, and curing/handling?and includes an extensive assessment of current and future markets. References: Territorial Seed. Sweet Potato Culture. http://www.territorialseed.com/stores/1/Sweet_Potato_Culture_Informati_W76C28.cfm?UserID=16178740&jsessionid=8c30d0f20f42$BE$22$0 B. Lerner. Dig Those Sweet Potatoes. Purdue Department of Horticulture and Landscape Architecture. 10-04-2001