When To Plant Onions In Oregon

If you’re wondering when to plant onions in Oregon, you’ve come to the right place. The timing is crucial for getting big, healthy bulbs, and it depends heavily on where you live in our diverse state.

Oregon’s climate ranges from wet coastal zones to dry high deserts, and each area has its own planting schedule. Getting your onions in at the right moment sets them up for success, leading to a fantastic harvest later in the summer. Let’s break down the best times for your specific region.

There are two main ways to start onions: from seeds, sets (small bulbs), or transplants. Your choice affects your planting date.

From Seed (Indoors): Start seeds indoors 10-12 weeks before your last spring frost. This gives them a long head start.
From Sets or Transplants: These go directly into the garden soil in early spring, as soon as the ground is workable.

Onions are categorized by day length: long-day, short-day, and day-neutral. For Oregon, long-day varieties are generally best because they bulb up as days get longer in our northern latitude.

Oregon’s Climate Zones and Planting Dates

Oregon is split into distinct growing regions. Here’s when to plant in each one.

Western Oregon (Willamette Valley, Portland, Coastal Areas)

This region has mild, wet winters and dry summers. The last frost is typically in mid-April.

Start Seeds Indoors: Early January to mid-February.
Plant Transplants/Sets Outdoors: Late March through April. You can plant as soon as the soil is no longer soggy.
Direct Seed Outdoors: Not usually recommended due to the long season required, but if you do, aim for early spring.

Central and Eastern Oregon (High Desert)

This area has cold winters, a shorter growing season, and a last frost date that can stretch into late May.

Start Seeds Indoors: Late February to March.
Plant Transplants/Sets Outdoors: Mid-April to May, after the danger of a hard freeze has passed.

Southern Oregon (Rogue Valley)

With warmer temperatures and an earlier last frost (often early April), you can get a jump on the season.

Start Seeds Indoors: December to January.
Plant Transplants/Sets Outdoors: February to March. The milder winters allow for very early planting.

Step-by-Step Planting Guide

Follow these steps for a successful onion patch.

Choose Your Onion Type: Select long-day varieties like ‘Walla Walla Sweet’, ‘Yellow Sweet Spanish’, or ‘Copra’ for most of Oregon. Day-neutral types like ‘Candy’ or ‘Superstar’ are also excellent choices statewide.
Prepare the Soil: Onions need loose, well-draining soil with lots of organic matter. Work in compost a few weeks before planting. They prefer a soil pH between 6.0 and 7.0. A raised bed is ideal for improving drainage, especially in clay soils.
Plant Correctly: For sets or transplants, plant them about 1 inch deep and 4-6 inches apart. Rows should be 12-18 inches apart. If you started seeds indoors, harden off the seedlings for a week before transplanting them outside.
Water and Feed: Water consistently, about 1 inch per week. Use a nitrogen-rich fertilizer early in the season to support green growth, but stop feeding once the bulbs begin to form.
Weed Carefully: Onions have shallow roots. Hand-pull weeds regularly so they don’t compete for nutrients.

Common Mistakes to Avoid

Even experienced gardeners can make a few errors with onions. Here’s what to watch out for.

Planting at the Wrong Depth: Don’t bury sets or transplants too deep. The neck (where the leaves meet the bulb) should be just at the soil surface.
Using the Wrong Day-Length Type: Planting a short-day onion in Oregon will cause it to bulb too early, resulting in very small onions.
Inconsistent Watering: Letting the soil dry out completely then flooding it can cause bulbs to split or become bitter.
Not Thinning: If you direct seed, you must thin the seedlings to the proper spacing. Crowded onions won’t develop properly.

Seasonal Care and Harvest Tips

Your work after planting ensures a good yield.

Spring and Early Summer Care

Keep the area weed-free and maintain even moisture. A layer of straw mulch can help with both weeds and water retention. Side-dress with a light fertilizer if growth seems slow.

Knowing When to Harvest

In late summer, you’ll see the tops start to yellow and fall over. This is the signal. Gently loosen the soil and lift the bulbs. Let them cure (dry) in a warm, airy, shaded place for about two weeks until the necks are tight and the outer skins are papery.

Storing Your Oregon Onions

After curing, trim the roots and cut the tops down to about an inch. Store them in a cool, dry, dark place with good air circulation, like a mesh bag or a single layer in a crate. Properly cured long-day onions can last for many months.

FAQ: Planting Onions in Oregon

Can I plant onions in the fall in Oregon?
In mild parts of Western and Southern Oregon, you can plant overwintering varieties (like ‘Egyptian Walking’ or specific multiplier onions) in the fall for a very early summer harvest. Standard bulb onions are typically a spring crop here.

What is the best onion for Oregon gardens?
‘Walla Walla Sweet’ is a famous and reliable choice for much of the state, especially western regions. For storage, ‘Copra’ and ‘Red Wing’ are excellent. Always check the day-length classification before buying.

Why are my onions so small?
Small bulbs are often caused by planting the wrong day-length type, planting too late, overcrowding, or insufficient nitrogen early in the growth cycle. Make sure your getting the timing and spacing right.

Can I grow onions in containers in Oregon?
Absolutely. Choose a deep container (at least 10-12 inches) and a well-draining potting mix. Plant sets or transplants at the same spacing, and be vigilant about watering, as pots dry out faster.

How do I deal with Oregon’s spring rains?
Good drainage is key. Raised beds are your best defense against soggy soil, which can rot onion bulbs. If you have heavy clay, amend it generously with compost to improve texture.

By matching your planting schedule to Oregon’s unique regional climates and following these simple steps, you’ll be well on your way to a bountiful onion harvest. The sweet taste of a homegrown onion is worth the wait.