Getting your potato planting timing right is the single biggest factor for a great harvest. If you’re wondering when to plant potatoes in Portland Oregon, you’re in the right place. Our unique maritime climate with its wet springs and mild summers creates a perfect, but specific, window for planting. Plant too early, and your seed potatoes might rot in cold, soggy soil. Plant too late, and they’ll battle summer heat before they’re ready. This guide will walk you through the simple steps to nail the timing and care for a successful spring harvest.
When to Plant Potatoes in Portland Oregon
For a classic spring harvest, the ideal planting time in the Portland area is typically from mid-March through April. We aim for a soil temperature of around 45°F (7°C). A good rule of thumb is to plant about 2-4 weeks before your last average spring frost date. For Portland, the last frost usually falls between April 15th and May 1st, but it can vary by your specific microclimate.
Watch nature’s cues. When the leaves on the oak trees are about the size of a squirrel’s ear, or when dandelions start blooming consistently, soil conditions are often becoming favorable. Don’t rush to plant in February if we have a warm spell—a cold, wet snap often follows and can spell disaster for your seed potatoes.
Understanding Portland’s Growing Seasons
Portland’s climate allows for more than one potato planting. Knowing these seasons helps you plan.
- Spring Planting (for Summer Harvest): This is the main event. Plant mid-March to April for harvesting from July through August. This is the focus of our guide.
- Early Summer Planting (for Fall Harvest): You can plant fast-maturing varieties in late June to early July for a late fall harvest. This avoids some pest issues but requires consistent watering during summer’s heat.
- Overwintering (Experimental): Some gardeners plant in fall for a very early spring harvest. This is risky due to winter rot and is not recommended for beginners.
Choosing the Right Potato Varieties
Selecting varieties suited to our climate and your taste will make you more successful. All potatoes fall into categories based on how long they take to mature.
- Early Season (65-80 days): Great for getting a quick harvest before peak summer heat. Try ‘Yukon Gold’, ‘Red Norland’, or ‘Irish Cobbler’.
- Mid-Season (80-95 days): A reliable choice for our long summer days. Includes favorites like ‘Kennebec’, ‘Purple Majesty’, and ‘Yellow Finn’.
- Late Season (95+ days): These need our longest, warmest days and are best for storage. ‘Russet Burbank’ and ‘German Butterball’ are excellent options.
Always buy certified disease-free seed potatoes from a garden center or reputable online source. Don’t use potatoes from the grocery store, as they are often treated to prevent sprouting and can carry disease.
Step-by-Step Planting Guide
Follow these steps to get your potatoes off to a strong start.
1. Pre-Sprouting (Chitting)
About 3-4 weeks before your planned planting date, set your seed potatoes in a cool, bright place (like a windowsill) to sprout. Place them with the “eyes” facing up. This gives them a head start, leading to faster growth once planted.
2. Preparing the Soil and Site
Potatoes need loose, well-draining soil with lots of organic matter. They thrive in full sun (at least 6 hours).
- Work the soil to a depth of 12 inches, removing rocks and clumps.
- Mix in several inches of finished compost or well-rotted manure. Avoid fresh manure, as it can cause scab disease.
- If your soil is heavy clay, consider planting in raised beds or large containers for better drainage.
3. The Planting Process
- On planting day, cut larger seed potatoes into pieces, ensuring each piece has at least 2-3 eyes. Let the cut pieces air-dry for a day to form a callus.
- Dig a trench about 6 inches deep.
- Place seed pieces cut-side down, eyes facing up, 12 inches apart in the trench.
- Space trenches about 2-3 feet apart.
- Cover the seed pieces with 4 inches of soil. Do not fill the trench completely yet.
Caring for Your Growing Potatoes
Consistent care after planting is simple but crucial.
Watering and Hilling
Water deeply once a week, aiming for about 1-2 inches of water, especially once foliage is growing. The most important task is “hilling.” When green shoots reach about 6-8 inches tall, gently mound soil from around the plant up around the stems, leaving just the top few leaves exposed. Repeat this process every few weeks. Hilling prevents sunlight from reaching the developing tubers (which turns them green and toxic) and encourages more potatoes to form along the buried stem.
Fertilizing and Pest Watch
A balanced, low-nitrogen fertilizer at planting is helpful. Too much nitrogen leads to lots of leaves and few potatoes. Keep an eye out for common pests like Colorado potato beetles (hand-pick them) and aphids. Good crop rotation (don’t plant potatoes in the same spot more than once every 3 years) is your best defense against soil-borne diseases.
Harvesting Your Bounty
Your harvest time depends on the variety you planted.
- New Potatoes: For tender, small “new” potatoes, you can gently dig around the plants about 2-3 weeks after they finish flowering.
- Mature Potatoes (for Storage): Wait until the plant’s foliage has completely yellowed and died back. Then, on a dry day, use a garden fork to carefully dig up your full harvest. Let them cure on the soil surface for a few hours, then brush off dirt and store in a cool, dark, well-ventilated place.
FAQ: Portland Potato Planting
Can I plant potatoes in May in Portland?
Yes, but it’s getting late for a spring planting. Opt for early or mid-season varieties and be prepared to water more frequently during summer heat. A July planting is better for a fall harvest.
What if we have a late frost after I’ve planted?
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 to protect them. They will usually recover from minor damage.
Can I grow potatoes in containers on my patio?
Absolutely! Use a large container (at least 10-15 gallons) with excellent drainage. Follow the same planting and hilling principles, using a quality potting mix. Container potatoes often need more frequent watering.
How do I know if my soil is warm enough?
Use a soil thermometer for the best gauge. If you don’t have one, the old-fashioned test works: if you can comfortably sit bare-bottomed on the soil, it’s warm enough. A more practical test is if the soil is workable and not waterlogged.
By following these guidelines and paying attention to Portland’s unique weather patterns each year, you’ll be well on your way to a plentiful potato harvest. Remember, gardening is part science and part observation, so don’t be afraid to adjust based on what you see in your own backyard. The reward of digging up your own homegrown spuds is well worth the wait.