If you’re planning your garden in the Pacific Northwest, knowing when to plant potatoes in Washington State is the key to a successful crop. Getting the timing right ensures your plants grow strong and produce a generous harvest before the fall rains arrive.
Washington’s unique climate, with its wet springs and varying winter hardiness zones, makes timing crucial. Plant too early, and your seed potatoes might rot in cold, soggy soil. Plant too late, and they won’t have enough time to mature. This guide will walk you through the simple steps to perfect your potato planting schedule.
When To Plant Potatoes In Washington State
The best time to plant potatoes in Washington is from late February through mid-April. However, this window shifts significantly depending on where you live. The goal is to plant about 2-4 weeks before your region’s last expected spring frost date.
Soil temperature is a more reliable guide than the calendar. You want the soil to be consistently at least 45°F (7°C). A simple soil thermometer can take the guesswork out of this.
Regional Planting Windows Across Washington
Washington’s diverse geography creates three main planting zones for potatoes.
- Western Washington (West of the Cascades): This includes the Puget Sound area and the coast. The maritime climate means milder winters but cooler, wetter springs. Aim to plant from mid-March to late April. Focus on well-drained soil to combat the spring rain.
- Eastern Washington (East of the Cascades): This region has a continental climate with colder winters and hotter, drier summers. Here, you can often plant a bit later, from early April to early May, once the soil warms up and dries out from snowmelt.
- Coastal Areas: The immediate coast has the most temperate conditions. You can usually start as early as late February or early March, taking advantage of the longer growing season.
Understanding Your Frost Dates and Hardiness Zone
Your local last frost date is your best friend for timing. You can find it through your county extension office or a quick online search. Planting 2-4 weeks before this date gives potatoes a head start in cool soil they love.
Washington spans USDA hardiness zones from 4b in the coldest mountain areas to 9a on the coast. Most population centers are in zones 6b to 8b. Knowing your zone helps you choose potato varieties with the right “days to maturity” for your area’s frost-free period.
Choosing the Right Potato Varieties for Washington
Selecting varieties suited to Washington’s climate improves your harvest. Consider both the growing season length and your culinary preferences.
- Early Season (65-80 days): Great for all regions, especially areas with shorter summers. Plant these first. Examples: ‘Yukon Gold’, ‘Red Norland’, ‘Irish Cobbler’.
- Mid-Season (80-95 days): A reliable choice for most gardens. Examples: ‘Kennebec’, ‘Viking Purple’, ‘Yellow Finn’.
- Late Season (95+ days): Best for Eastern Washington’s long, hot summers or Western WA if planted early. Examples: ‘Russet Burbank’, ‘German Butterball’, ‘All Blue’.
Step-by-Step Guide to Planting Your Potatoes
Once your timing is set, follow these steps for a great start.
- Chit Your Seed Potatoes: About 2-3 weeks before planting, place your certified disease-free seed potatoes in a cool, bright spot. This encourages short, sturdy sprouts, giving them a vigor boost.
- Prepare the Soil: Potatoes need loose, well-drained soil with a slightly acidic pH (5.8-6.5). Work in several inches of compost or well-rotted manure. Avoid fresh manure, as it can cause scab disease.
- Cut and Cure (Optional): Larger seed potatoes can be cut into pieces, each with at least 2-3 “eyes.” Let them cure for a day or two so the cut surface callouses over, preventing rot.
- Plant Correctly: Dig a trench or individual holes about 6-8 inches deep. Place seed pieces eye-side up, 12 inches apart. Rows should be 2-3 feet apart. Cover with 4 inches of soil.
- Hill as They Grow: When plants are 6-8 inches tall, mound soil around the stems, leaving a few inches of leaves exposed. Repeat this every few weeks. This protects tubers from sunlight (which turns them green and toxic) and encourages more potato production.
Common Mistakes to Avoid
A few simple missteps can reduce your harvest. Here’s what to watch for.
- Planting in cold, waterlogged soil. This is the leading cause of seed piece rot.
- Using grocery store potatoes. They are often treated with sprout inhibitors and may carry disease.
- Neglecting to hill the plants. Exposed tubers will turn green and be inedible.
- Overwatering early on, or underwatering when tubers are forming (during flowering).
Optimal Harvest Timing for Maximum Yield
Knowing when to plant is only half the battle; knowing when to harvest completes the cycle.
For “new” or baby potatoes, you can gently dig around plants about 2-3 weeks after they finish flowering. For mature, storage potatoes, wait until the plant’s foliage turns yellow and begins to die back. This usually happens in late summer or early fall.
Cut the dead foliage off and wait 10-14 more days for the skins to toughen up underground. Then, choose a dry day to dig your harvest. Be careful not to puncture the tubers with your fork or shovel.
Curing and Storing Your Washington-Grown Potatoes
Proper curing ensures your potatoes last through winter. After digging, brush off excess soil—don’t wash them. Let them cure in a dark, well-ventilated place with high humidity (about 85-95%) for 10-14 days. This allows minor cuts to heal and skins to fully set.
After curing, store them in a cool (38-45°F), dark, and humid place. A basement or root cellar is ideal. Check them periodically and remove any that are softening or sprouting to prevent spoilage from spreading.
FAQ: Planting Potatoes in Washington State
Can I plant potatoes in the fall in Washington?
In most of Washington, fall planting is not recommended due to wet winters that cause rot. However, in some very mild coastal areas, a late summer planting for a fall harvest can sometimes work with careful variety selection.
What if my potato plants get hit by a late frost?
Potato foliage is sensitive to frost. If a late frost is forecast after your plants have emerged, cover them with row cover, cloth, or even a light layer of straw. They will often recover and send up new growth if the frost was not too severe.
How often should I water my potato plants?
Water consistently, providing about 1-2 inches per week. Increase watering when tubers begin to form (around flowering time). The most important thing is to ensure soil stays evenly moist but never waterlogged, which is a common challange in Western WA springs.
Can I grow potatoes in containers in Washington?
Absolutely! Container growing is an excellent option, especially if you have heavy, poorly drained soil. Use a large container (at least 10-15 gallons) and follow the same planting and hilling principles. Containers also warm up faster in spring, allowing for slightly earlier planting.
By aligning your planting schedule with Washington’s regional climates and following these straightforward steps, you’ll be well on your way to a productive potato patch. The reward of digging up your own homegrown spuds is well worth the planning.