Oregon · zones 6a–9a
When to plant onions in Oregon.
Sow or transplant between Feb 5 to Mar 21 in a typical year, keyed to Oregon's median last frost around Apr 15. A second, fall sowing fits Aug 30 to Oct 11. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Oregon season.
1 · Start indoors
Dec 25 to Feb 7
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 5 to Mar 21
Keyed to the ~Apr 15 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 30 to Oct 11
Counted back from the ~Oct 25 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Oregon spans more than one climate: Zone 8 is the most common zone, but the state runs 6a to 9a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Oregon growing notes
Bulb onions decide when to stop growing leaves and start a bulb by counting hours of daylight, not by feeling for warmth, and this state's northern latitude only pays off with a variety built to read that count correctly.
Why the variety matters here before the spacing does
A half inch of soil covers onion seed here when started indoors, though many gardeners instead set out bare-root transplant bundles, and either way plants land 4 inches apart in the row. For the first stretch of its 95 days, the plant does nothing but build leaves, only shifting to building a bulb once day length crosses a point specific to its type.
Onions come in three day-length categories, short, intermediate, and long, and the category decides the outcome: the difference between a bulb the size of a fist and one that barely forms. This state sits far enough north to fall solidly in long-day country, so a short-day type suited to the Gulf Coast, or an intermediate type from the middle of the country, quits making leaves too early here and stalls with a small, unfinished bulb. A long-day variety waits for the length of day this far north provides, and it is the right choice no matter which window it goes in.
Spring is the default, but a fall-set bulb runs on its own clock
Spring carries most of the bulb onion crop here, a transplant set out once the ground has warmed enough to work, growing on through 95 days to a bulb ready for pulling and curing by late summer. This state also opens a fall window, unlike a second spring planting squeezed into a shorter run. A fall-set transplant spends the cold months as a small, rooted plant that barely grows, and only starts building its bulb the following year once day length climbs back past that same long-day mark.
Carrying a small onion plant through winter leans on the mild half of the state, the marine valleys and coast, where cold rarely bites hard enough to kill a young plant; east of the mountains, a harder freeze makes that same bet worse. Which variety to plant also depends on the bulb's purpose: Walla Walla Sweet, a Pacific Northwest standard, gives a mild, thin-skinned bulb best eaten fresh but keeps poorly, going soft within weeks of curing, while a storage type such as Copra holds in a cool, dry spot for months longer at some cost to that sweetness.
Two pests on the leaves, two diseases underground, and 15 pounds from a 10-foot row
Onion thrips matter most during any hot, dry stretch, rasping the leaf surface and leaving a silvery streaking that thickens into a dull, papery look if the population builds. A plant fighting heavy thrips bulbs smaller, since damaged leaves feed less into the bulb. Onion maggot works underground, a soil-dwelling larva tunneling into the base of a young transplant; the giveaway is a seedling that yellows from the base up and topples over, with a chewed, stubby root system where a healthy transplant would show firm white roots. A floating cover pinned over the row from planting day keeps the adult fly off the plants before it ever lays an egg, cheaper than treating a larva already inside.
Downy mildew shows on the leaves as pale, oval patches carrying a grayish-purple fuzz, most likely after cool, damp spring weather rather than later in summer. White rot is the one worth taking seriously the moment it turns up: a fluffy white growth low on the bulb, studded with what look like small black seeds. Nothing applied that season clears a confirmed case, and the fungus can sit in soil for years, so the real response is to stop planting alliums there rather than treat around it. At 4 inches between plants, a 10-foot row holds around 30 onions, and at half a pound each, that is roughly 15 pounds of cured bulbs from one row, before counting anything a fall-set planting adds the next summer.
In Oregon: watch for
The pests that find onions here.
A middle-length season, about 193 frost-free days, means onion, bulb overlaps onion thrips for a stretch each summer. Check plants every week or two and treat early.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: Oregon gives onions about 193 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in Oregon: questions
When should I plant onions in Oregon?+
In a typical Oregon year, sow onions or set out transplants between Feb 5 to Mar 21, keyed to the state's median last frost around Apr 15. There's also a fall window: Aug 30 to Oct 11. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Oregon?+
Start seeds inside about 6 weeks before set-out: roughly Dec 25 to Feb 7 for a typical Oregon season.
What USDA zone is Oregon?+
Oregon spans zones 6a–9a, mostly zone 8. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.