When to plant onions in Portland, Oregon
January 28 – February 11
Transplant outdoors · typical Portland yearClimate basis: NOAA station Portland Kgw-tv, OR (USC00356749), 1 mi (1 km) from downtown Portland (ZCTA 97204 centroid), elevation 159 ft, on the 1991–2020 climate normals. Plant onion sets or transplants from approximately the dates above, anchored to the median last spring 32°F freeze (February 25). One year in ten still freezes after March 21.
The Portland year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Mar 21
Every method, with its sources
Start seeds indoors
Nov 19 – Dec 3Sow 8–10 weeks (UNH) to 10–12 weeks (Minnesota) before planting out; derived from the −4-week set-out date using the UNH lead time. Anchored to the median last spring freeze (Feb 25). University of New Hampshire Extension · University of Minnesota Extension
Transplant outdoors
Jan 28 – Feb 11UNH: set out transplants (or sets) 4 weeks before the last frost; Purdue's hardy class allows 4–6 weeks before. The later UNH point is used, with a 14-day span. Anchored to the median last spring freeze (Feb 25). University of New Hampshire Extension · Purdue University Extension
Variety assumption: Assumes storage-type bulb onions (about 100–115 days from sets; Penn State lists 105).
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (3)
- University of New Hampshire Extension: Growing Vegetables: When to Plant Your Vegetable Garden [fact sheet] (accessed 2026-07-24)Per-crop 'time from seed to transplant' and 'safe to set out in garden' relative to last frost.
- University of Minnesota Extension: Growing onions (accessed 2026-07-24)"You can also raise your own transplants by starting seed indoors 10 to 12 weeks before planting outside."
- Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.