Oregon planting calendar

When to plant onions in Oregon — sow, transplant & harvest dates

Oregon is mostly USDA zone 8b (range 4b-9b). Dates below are derived from onions's frost tolerance and Oregon's frost window — not generic national averages.

Onions planting timetable for Oregon

Stage	When in Oregon	Anchor
Start seeds indoors	early February (February 4)	10 weeks before the last frost (mid-April (Willamette Valley))
Transplant outside	mid-March (March 18)	28 days before the last frost (mid-April (Willamette Valley))
First harvest (estimate)	early July (July 6)	~110 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Oregon's climate shifts the onions dates

Oregon's last spring frost averages mid-April (Willamette Valley) and first fall frost early November (Willamette Valley), which sets the whole planting clock. Oregon is split by the Cascades: a mild, wet, long-season west and a cold, dry, short-season high desert east. Sow early — onions bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Don't plant before mid-April (Willamette Valley) — a hard freeze can still set young plants back. In the high desert and Cascades east of the mountains (zone 4b) the safe date runs a week or two later.

Regional variation within Oregon

the high desert and Cascades east of the mountains (zone 4b) runs roughly 1-2 weeks behind the state average; the Willamette Valley and southwest interior (zone 9b) can plant 1-2 weeks earlier.

Portland — USDA zone 9a
Eugene — USDA zone 8b
Salem — USDA zone 8b
Bend — USDA zone 6b
Medford — USDA zone 8a

What else to plant in Oregon around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in Oregon?

In Oregon (mostly USDA zone 8b), sow onions indoors around early February, transplant outdoors mid-March (before the last frost, mid-April), and harvest from early July. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Oregon?

Most of Oregon sits in USDA hardiness zone 8b, with the state spanning roughly 4b-9b from the high desert and Cascades east of the mountains (zone 4b) to the Willamette Valley and southwest interior (zone 9b). The last spring frost averages mid-April (Willamette Valley) and the first fall frost early November (Willamette Valley).

Can you grow onions in Oregon?

Yes. Oregon's dominant zone 8b supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Oregon?

the high desert and Cascades east of the mountains (zone 4b) runs roughly 1-2 weeks behind the state average; the Willamette Valley and southwest interior (zone 9b) can plant 1-2 weeks earlier.

What else can I plant in Oregon around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.