Potatoes are a popular crop in Washington, as they grow well in the state’s cool, moist climate. Potatoes are generally planted in early spring and harvested in late fall, with some varieties maturing as early as July. For the best results, potatoes should be planted in well-drained, sandy-loam soil with a pH of 5.0-7.0. To ensure an abundant harvest, it is important to use certified seed potatoes, as regular potatoes may contain disease or be of poor quality.
Once planted, potatoes require about an inch of water a week, as well as regular weeding, chilling, and fertilizing. With proper care, Washington growers can expect a bountiful harvest of potatoes.
Washington’s Hardiness Zones And Climate
Washington is a diverse state with a wide range of climates and growing zones. Zone 4a is the coldest zone in the state, located in the northern and eastern parts of the Cascade Mountains. This zone experiences cold, snowy winters, with temperatures down to -20°F or lower, and mild summers with temperatures in the mid-70s. The growing season is relatively short, lasting from mid-May to mid-September.
Zone 5a is located in the eastern part of the state and experiences similar temperatures to zone 4a, though the coldest temperatures may drop to -15°F. The growing season is slightly longer, stretching from mid-April to mid-October.
Zone 6a is located in the western part of the state and experiences milder winters and longer growing seasons. Winters may reach temperatures as low as 0°F, while summers may reach temperatures in the high 80s. The growing season typically runs from mid-March to mid-November.
Zone 7a is located in the lowlands of the Puget Sound region. Winters are mild, reaching temperatures in the mid to low 30s, while summers may reach the mid to high 80s. The growing season is typically from mid-February to mid-October.
Zone 8a is located in the warmer parts of western Washington, near the coast. Winters are mild with temperatures reaching the mid-40s, while summers may reach the mid to high 80s. The growing season typically runs from mid-January to mid-September.
Zone 9b is located in the warmest parts of the state, near the Oregon border. Winters are mild with temperatures reaching the high 40s, while summers may reach the low 90s. The growing season typically runs from mid-December to mid-August.
Different varieties of seed potatoes
When selecting seed potatoes for growing in Washington, it is important to be mindful of the variety’s days to harvest and the length of time you have before you want to harvest them.
Early-season varieties such as ‘Yukon Gold’ and ‘Red Norland’ have fewer days to harvest and should be planted as soon as possible for harvesting in late summer.
Mid-season varieties such as ‘Russet Burbank’ and ‘Kennebec’ have more days to harvest and should be planted in late April or early May for harvesting in fall.
Late-season varieties such as ‘Cara Russet’ and ‘All Blue’ have the most days to harvest and should be planted in late April or early May for harvesting in early winter. Be sure to select varieties with the right number of days to harvest for your intended harvest date. Some good potato varieties for Washington include:
- Russet Potatoes: 85-95 days
- Yukon Gold Potatoes: 90-110 days
- Red Potatoes: 80-90 days
- Purple Potatoes: 90-110 days
- Fingerling Potatoes: 90-120 days
- Sweet Potatoes: 90-120 days
- White Potatoes: 90-100 days
- All-Blue Potatoes: 95-105 days
- Yellow Finn Potatoes: 85-95 days
- Kennebec Potatoes: 85-95 days
When To Plant Potatoes In Washington
The best time to plant potatoes in Washington is in mid-April. Potatoes should be planted as soon as the soil can be worked and when nighttime temperatures are consistently above 40°F. Early potatoes can be planted as soon as the soil can be worked, usually in mid-March. In regions with short growing seasons, such as in the Puget Sound lowlands and eastern Washington, potatoes can be planted as late as mid-May.
- Zone 4: Around April 30th
- Zone 5: Around April 15th
- Zone 6: Around April 7th
- Zone 7: Around March 24th
- Zone 8: Around March 14th
- Zone 9: Around February 14th
How To Plant Potatoes In Washington
Begin the planting process for seed potatoes by tilling the soil to a depth of 8 inches and incorporating organic compost. Once you have done this, find a sunny location that receives at least 8 hours of direct sunlight and place the seed potatoes.
Plant the seed potatoes with the “eyes” facing upward, leaving a distance of 8 to 10 inches in between each. Cover the seed potatoes with a layer of soil that is 3-4 inches thick, and make sure to water them adequately. As the potatoes start to sprout, add more soil to the rows to keep them adequately buried.
Water the potatoes on a regular basis and remove any weeds from the area. For those living in hot and dry climates, you may want to cover the soil around the potatoes with straw, although this is not essential.
Caring For Potato Plants
Caring for potato plants is pretty easy – they’re incredibly hardy and generally no-fuss. Potato plants need full sun and well-drained soil to thrive. They should be watered deeply and regularly, allowing the soil to dry out between waterings.
Fertilizing is also important for optimal growth. Potato plants need a balanced fertilizer with equal parts nitrogen, phosphorus, and potassium. This should be applied every four to six weeks, depending on the soil’s nutrient content.
It is also important to keep the soil evenly moist, as potatoes do not tolerate dry or waterlogged conditions. Mulching around the potato plants can help retain moisture and reduce weeds.
When To Harvest Potatoes In Washington
There are two sure ways to know your potatoes are about ready to harvest! The first is counting backward from your current date to their planting date. Potato varieties have an approximate number of days to harvest, so consult the days to harvest for the particular variety of potatoes you’ve planted. If you aren’t sure, assume it’s around 100 days.
The appearance of your potato plants is another dead giveaway. You will know your potatoes are ready to harvest when the foliage begins to turn yellow and die back. Your plants will go through an entire flowering cycle, which is nice because the flowers are really beautiful.
Allow the soil around the plants to dry before harvesting, but don’t allow it to be dry for too long. Once harvested, inspect the potatoes carefully- they should be firm and free of green or soft spots.
Carefully dig up the potatoes with a garden fork, taking care not to damage the potatoes in the process. Once the potatoes have all been dug up, brush off any excess soil and inspect them for any damage. Discard any potatoes that are damaged, as these are not suitable for long-term storage.
Finally, gently place the potatoes in a cool, dry, and dark area for storage. It is important to only store undamaged potatoes, as damaged potatoes can quickly rot.