When to plant in Lake Oswego, OR
USDA Zone 9aHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Lake Oswego, Oregon — all computed from Lake Oswego's nearest NOAA weather station.
Lake Oswego enjoys a long ~245-day frost-free season — you can succession-sow, fit in a second crop, and grow long-season heat-lovers with room to spare. Zone 9a is warm enough that Lake Oswego can grow subtropical perennials, and the short (or absent) frost period barely limits the annual calendar.
Frost probability
OREGON CITY · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Lake Oswego’s own odds, recorded at OREGON CITY.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 4 | Apr 15 | Mar 26 | Oct 16 | Oct 31 | Nov 20 |
| 32°F | Apr 11 | Mar 18 | Feb 19 | Oct 30 | Nov 18 | Dec 12 |
| 28°F | Mar 7 | Feb 12 | Jan 1 | Nov 16 | Dec 8 | Jan 5 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Lake Oswego, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 12 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Lake Oswego planting FAQ
When is the last spring frost in Lake Oswego, OR?
Plan for the last spring frost in Lake Oswego around March 18 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Lake Oswego, OR?
Expect Lake Oswego's first fall frost near November 18 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Lake Oswego in?
Lake Oswego is in USDA hardiness zone 9a. In zone 9a, winters are mild — many tender perennials overwinter here.
How long is the growing season in Lake Oswego?
There are roughly 245 frost-free days in Lake Oswego (a long growing season), running from the average last frost around March 18 to the first fall frost near November 18.
When should I plant tomatoes in Lake Oswego?
In Lake Oswego, start tomato seeds indoors around January 21–February 4, then transplant seedlings outdoors around March 25 once the danger of frost has passed.
Never miss a window in Lake Oswego
An email when it’s time to start seeds, transplant, and sow — timed to Lake Oswego’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reachFrost dates recorded at OREGON CITY, 10 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Lake Oswego, OR — Frost Dates & Zone 9a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00356334. Retrieved from https://blissgarden.com/oregon/lake-oswego.