When To Plant Potatoes In The Northwest – Optimal Timing For Planting

Knowing when to plant potatoes in the northwest is the single most important factor for a successful harvest. Get the timing right, and you’ll be rewarded with a bounty of spuds; get it wrong, and you might face disappointing yields or disease. This guide will walk you through the optimal windows for your specific area, from the maritime coasts to the inland valleys.

The Pacific Northwest’s climate is wonderfully diverse, but that means planting dates can vary by several weeks. We’ll break it down so you can plant with confidence.

When to Plant Potatoes in the Northwest

This heading is your golden rule. For most of the region, the traditional planting period falls between late March and early May. However, you should always use soil temperature and local frost dates as your true guides, not just the calendar.

Understanding Your Northwest Microclimate

The “Northwest” isn’t one place. Your specific conditions depend heavily on whether you’re on the coast, in the inland valleys, or at a higher elevation.

• Coastal Areas (Western WA/OR, BC Coast): Milder winters and cooler summers. You can often plant a bit earlier, from mid-March to mid-April, as the ground warms. Watch for excessive spring rain, which can rot seed pieces.
• Inland Valleys (Willamette, Puget Sound, interior BC): This is prime potato country. Aim for early April to early May. The soil warms nicely but summer heat isn’t usually extreme.
• Higher Elevations & Eastern Zones: Later frosts are a real concern here. Wait until mid-May or even early June. The growing season is shorter, so choose faster-maturing varieties.

The Two Best Signs It’s Time to Plant

Nature gives you clearer signals than any date on a page. Look for these two indicators.

1. Soil Temperature is Above 45°F (7°C): This is critical. Use a soil thermometer. Potatoes planted in cold, soggy soil will just sit there and risk rotting. A consistent 45-50°F is ideal.
2. Daffodils are Blooming: A classic gardener’s proverb. When daffodils are in full flower, the soil has usually warmed enough for potato planting. It’s a handy, natural calendar.

How to Prepare for Planting

Good preparation sets the stage. A few weeks before your target date, start getting ready.

• Choose Your Seed Potatoes: Always use certified disease-free seed potatoes from a garden center, not grocery store spuds. They’re treated to prevent problems.
• “Chit” or Green Them: Place seed potatoes in a cool, bright spot for 2-4 weeks. This encourages strong, stubby sprouts, giving them a head start.
• Prep the Soil: Potatoes need loose, well-draining soil. Work in plenty of compost or well-rotted manure. Avoid fresh manure, as it can cause scab.

Step-by-Step Planting Guide

1. Dig a trench about 6-8 inches deep.
2. Place seed pieces (cut side down) or whole small potatoes 12 inches apart in the trench.
3. Cover with 4 inches of soil.
4. As the plants grow to about 6 inches tall, gradually hill soil around the stems, leaving a few inches of leaves exposed. This protects tubers from sun and encourages more potatoes.

Choosing the Right Varieties for the Northwest

Some potato types perform exceptionally well in our climate. Consider these categories.

• Early Season (60-80 days): ‘Yukon Gold’, ‘Red Norland’. Great for coastal areas or getting a early summer harvest.
• Mid-Season (80-100 days): ‘Kennebec’, ‘German Butterball’. Reliable workhorses for the inland valleys.
• Late Season (100+ days): ‘Russet Burbank’, ‘All Blue’. Need the long, warm summers of the interior valleys.

What If You Plant Too Early or Too Late?

Mistakes happen, but knowing the consequences helps.

Planting too early in cold, wet soil is the most common error. It can lead to seed piece decay, slow growth, and vulnerability to disease. If a surprise late frost hits after foliage emerges, cover plants with row cover or even newspaper overnight.

Planting to late means your potatoes will try to form tubers in the hottest part of summer. This can reduce yields. It also pushes your harvest into the wet fall, increasing the chance of rot before you can dig them up.

Succession Planting for a Longer Harvest

You don’t have to plant all your potatoes at once. Try succession planting for a continuous supply.

1. Plant your first batch in early spring.
2. Plant a second batch of early varieties about 2-3 weeks later.
3. You can even plant a small crop of early potatoes in late summer (early August) for a fall harvest in milder coastal and valley areas.

Caring for Your Potato Crop

Once planted, potatoes need consistent moisture, especially when tubers are forming. Water deeply once a week if rain is absent. Mulch with straw to conserve moisture, suppress weeds, and keep soil cool. Watch for pests like Colorado potato beetles and remove them by hand.

Knowing When to Harvest

Harvest “new” potatoes when plants flower. For mature, storage potatoes, wait until the plant tops have completely died back. Use a garden fork to gently lift the tubers on a dry day. Let them cure in a dark, ventilated place for 1-2 weeks before storing.

FAQ: Your Northwest Potato Questions Answered

Can I plant potatoes from the grocery store?

It’s not recommended. They are often treated with sprout inhibitors and may carry disease that can linger in your soil for years. Certified seed potatoes are a safer investment.

What is the latest date to plant potatoes in Washington state?

For a main crop, late June is pushing it, even in western Washington. For a early fall harvest of small potatoes, you might try mid-July with a fast-maturing variety, but success depends on a mild autumn.

How do I protect potatoes from late spring frost?

If green foliage emerges and a frost is forcasted, simply cover the plants with floating row cover, cloth, or even a temporary layer of straw. Remove it once the morning temperatures rise.

Should I cut my seed potatoes?

You can cut larger seed potatoes, ensuring each piece has at least 2-3 “eyes.” Let the cut pieces cure for a day or two so the cut surface calluses over, which helps prevent rot. Small, egg-sized potatoes can be planted whole.

Getting your potato planting timing correct in the Northwest is mostly about observing your local conditions. By following the soil temperature rule and understanding your microclimate, you’ll set your crop up for a productive season. With a little planning and these tips, you’ll be on your way to a fantastic homegrown harvest that lasts for months.