When To Plant Onions In Washington State – For Optimal Harvest Timing

Knowing when to plant onions in Washington State is the single most important factor for a successful crop. Getting the timing right ensures your bulbs have enough cool weather to grow big and enough warm weather to mature properly.

Washington’s diverse climates, from the wet west to the dry east, make a one-size-fits-all date impossible. But by understanding a few key principles, you can confidently schedule your planting for an optimal harvest.

When To Plant Onions In Washington State

This core timing depends on whether you’re starting from seeds, sets, or transplants, and which of Washington’s growing regions you call home. Onions are categorized by day-length—a crucial detail for our northern latitude.

Understanding Onion Day-Length for the Pacific Northwest

Onions bulb up in response to daylight hours. Washington gardeners need to choose the right type:

• Long-Day Onions: These are essential for most of Washington. They form bulbs when daylight lasts 14-16 hours. Perfect for our summer days.
• Intermediate-Day Onions: Can work in some areas, especially with later plantings, but long-day types are the most reliable choice.
• Short-Day Onions: Best for southern states. They will bulb too early here, producing small onions.

Always select long-day varieties like ‘Walla Walla Sweet’, ‘Copra’, ‘Yellow Sweet Spanish’, or ‘Redwing’.

Regional Planting Windows Across Washington

Our state has two primary gardening climates, divided by the Cascade Mountains.

Western Washington (West of the Cascades)

This region has milder, wetter winters and cooler springs. The key is to plant as early as the soil can be worked.

• Seeds Indoors: Start seeds indoors around mid-January to early February. This gives transplants a strong head start.
• Transplants & Sets Outdoors: Plant hardened-off transplants or onion sets into the garden from late February through March. If the ground isn’t frozen or waterlogged, get them in.
• Direct Seeds Outdoors: You can sow seeds directly in the garden in March or early April, but bulbing will be later and bulbs may be smaller.

Eastern Washington (East of the Cascades)

This region experiences colder winters, hotter summers, and a shorter spring. Planting happens a bit later.

• Seeds Indoors: Start seeds indoors in early to mid-February.
• Transplants & Sets Outdoors: Aim to plant from late March through April. Wait for the soil to dry out and warm up slightly from winter frosts.
• Direct Seeds Outdoors: Sow directly in the garden from early to mid-April.

Step-by-Step Planting Guide

Follow these steps once your timing is set.

1. Prepare the Soil: Onions need loose, well-draining soil with lots of organic matter. Work in compost or aged manure. They prefer a slightly acidic to neutral pH (6.0-7.0). A balanced fertilizer at planting helps.
2. Planting Depth & Spacing: For sets and transplants, plant them so the tip is just barely visible above the soil. Space them 4-6 inches apart in rows 12-18 inches apart. For seeds, sow ½ inch deep and thin later.
3. Watering: Water immediately after planting. Keep the soil consistently moist (but not soggy) throughout the growing season, especially during bulb formation.
4. Weeding: Onions have shallow roots. Hand-weed carefully to avoid damaging them. A light mulch can supress weeds and retain moisture.

Optimal Harvest Timing and Signs

Your planting date dictates your harvest. Here’s how to know when your onions are ready.

• Green Onions (Scallions): You can harvest these any time once the tops are tall enough.
• Bulb Onions: Harvest is typically from late July through August in most of Washington. The plants will tell you: the tops will turn yellow, flop over, and begin to dry out.

When about half the tops have fallen over naturally, it’s time to finish the harvest. Some gardeners gently bend over the remaining tops to initiate final curing.

Curing and Storing Your Washington Onions

Proper curing is vital for storage. Don’t skip this step!

1. Gently lift bulbs from the soil on a dry, sunny day.
2. Lay them out in a single layer in a warm, dry, airy place out of direct rain. A covered porch, garage, or shed is ideal.
3. Let them cure for 2-4 weeks until the necks are completely tight and dry and the outer skins are papery.
4. Trim roots and cut tops back to about 1 inch. Store in a cool, dry, dark place in mesh bags or a single layer.

Well-cured long-day onions from your garden can last for many months.

Common Problems and Solutions in Washington

Watch for these regional issues:

• Damp Rot (Western WA): Ensure perfect drainage and avoid overwatering to prevent rot. Raised beds are a great solution.
• Onion Maggots: Use crop rotation and consider floating row covers at planting to deter this pest.
• Bolting: If an onion sends up a flower stalk too early, it’s often due to a sudden cold snap after growth starts. Harvest and use bolted onions quickly, as they don’t store well.

FAQ: Planting Onions in Washington State

Can I plant onions in the fall in Washington?

In very mild parts of Western Washington, you can experiment with planting overwintering varieties (like ‘Wall Walla’) in October for a very early summer harvest. It’s risky in colder zones, and not recommended for beginners or in Eastern WA.

What is the best onion variety for Washington?

The famous ‘Walla Walla Sweet’ is a well-adapted long-day heirloom. For storage, ‘Copra’ and ‘Paterson’ are excellent reliable choices that grow well here.

How late is too late to plant onions?

If planting sets or transplants, getting them in by mid-May at the absolute latest is crucial. Later plantings won’t have enough time to form sizeable bulbs before the day-length triggers bulbing.

Why are my onions so small?

Small bulbs are usually caused by planting the wrong day-length type (like short-day), planting too late, overcrowding, or insufficent water and nutrients during the growth phase.

By aligning your planting schedule with Washington’s unique regions and choosing the right onions, you’ll set the stage for a bountiful harvest. Paying attention to soil, water, and those all-important harvest signs will ensure you pull plump, flavorful bulbs from your garden all season long. Remember, the work you put in during those early spring days directly determines the size and quality of your crop come late summer.