When is the last frost in Lake Oswego, OR?

The average last spring frost (50% probability of 32°F) in Lake Oswego is around April 1, based on NOAA/NCEI 1991–2020 normals at the Beaverton 2 Ssw, OR station (5.4 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in Lake Oswego?

The average first fall frost in Lake Oswego, OR is around November 6, giving roughly a 222-day frost-free growing season.

What planting zone is Lake Oswego, OR?

Lake Oswego is in USDA plant hardiness zone 9a (average annual extreme minimum temperature 20 to 25°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Lake Oswego?

In Lake Oswego, OR the warmest month is August (avg high 80.6°F) and the coldest is January (avg low 37.3°F). It averages about 44.1″ of precipitation a year and 3.6″ of snow.

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Lake Oswego, OR Planting Calendar & Frost Dates

USDA hardiness zone 9a · ZIP 97035 · elevation 49′ · NOAA & USDA data

Lake Oswego is in USDA hardiness zone 9a (winters can dip to 20 to 25°F), with a growing season of about 222 days between the average last spring frost (April 1) and first fall frost (November 6). The warmest month is August (avg high 80.6°F); the coldest is January (avg low 37.3°F). It averages 44.1″ of precipitation a year and 3.6″ of snow, mostly mid-winter. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp 20 to 25°F

Last spring frost

April 1

avg (50% prob, 32°F)

First fall frost

November 6

avg (50% prob, 32°F)

Growing season

222 days

frost-free window

Warmest month

August

avg high 80.6°F

Month-by-month typical weather in Lake Oswego

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Portland Kgw-tv, OR (7.4 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	46.9	37.3	42.1	6.4	1.3
February	50.5	38.8	44.7	4.7	1.4
March	55.8	40.9	48.3	4.8	0
April	60.7	44.2	52.5	3.6	0
May	68	49.4	58.7	2.6	0
June	72.9	53.3	63.1	1.5	0
July	80.3	57.9	69.1	0.4	0
August	80.6	58.6	69.6	0.5	0
September	74.9	55.1	65	1.6	0
October	62.9	47.9	55.4	4	0
November	52.3	41.6	46.9	6.6	0
December	45.9	37.3	41.6	7.4	0.9

What to plant when in Lake Oswego

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: February 18 · Transplant out: April 8
Peppers	warm	Start seeds indoors: February 4 · Transplant out: April 15
Cucumbers	warm	Direct sow: April 8
Zucchini / squash	warm	Direct sow: April 8
Bush beans	warm	Direct sow: April 8
Sweet corn	warm	Direct sow: April 8
Basil	warm	Transplant out: April 8
Peas	cool	Sow (spring): February 25 · Sow (fall): September 11
Spinach	cool	Sow (spring): February 18 · Sow (fall): September 11
Lettuce	cool	Sow (spring): March 4 · Sow (fall): September 11
Kale	cool	Transplant (spring): March 11 · Sow (fall): August 28
Broccoli	cool	Transplant (spring): March 18
Carrots	cool	Sow (spring): March 11 · Sow (fall): August 28
Onions	cool	Transplant (spring): March 4
Potatoes	cool	Plant seed potatoes: March 18
Radishes	cool	Sow (spring): March 4 · Sow (fall): September 25

Dates are computed from Lake Oswego's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

Nearby cities in Oregon

Beaverton, OR Portland, OR Hillsboro, OR Gresham, OR Salem, OR Albany, OR Corvallis, OR Eugene, OR

Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — Beaverton 2 Ssw, OR, 5.4 mi (confidence: high). Monthly weather normals: Portland Kgw-tv, OR, 7.4 mi (confidence: high). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.