Portland, OR Frost Dates: Last Spring and First Fall Frost

Frost leaves Portland on February 25 and comes back on December 1 when the odds are even, a window of 280 days for tender plants.

Because half of all years do worse than the typical date, the dates that matter for tender plants are the late spring date, March 21, and the early fall date, November 10, each of which one year in ten fails to beat. Against a median of 229 days for the 100 cities on these pages, Portland has a season 51 days longer, 26th on the list.

NOAA measured them at Portland Kgw-TV (station USC00356749), about 2.3 miles south-west of the Census Bureau's internal point for Portland and about 160 feet above sea level.

When is the last frost in Portland?

One year in ten has a freeze on or after March 21. In nine years out of ten there is still a freeze on or after January 24, and half of years see one on or after February 25.

A span of 56 days from the 90% date to the 10% date is wide for these pages. Spring in Portland is less predictable than in most of the 100 cities, and the late date is 24 days past the typical one.

First fall frost in Portland

NOAA's early fall date for Portland is November 10, its even-odds date is December 1 and its late date is December 27; the first freeze has come by each of them in one, five and nine years out of ten.

From the 10% date to the 90% date is 47 days, a wide band here, and the early date arrives 21 days before the typical one.

Portland's frost-free season

A little more room than the middle of these pages, then, but not a different kind of garden. Season length swings more here than in most of the 100 cities: 280 days in a typical year, 245 days in a short one, a difference of 35 days.

These figures are NOAA's own counts of freeze-free days across its simulated years, which is why they can differ a little from the days between the two typical dates. Every winter in the record reached freezing at Portland Kgw-TV, so the dates above describe a real yearly event, not a rare one.

Hard freeze dates for Portland

Light frost and hard freeze are well separated in Portland. In fall the typical 28°F night comes on December 20, 19 days after the first 32°F frost on December 1; in spring the last one comes on January 31, 25 days before the last 32°F frost. Crops that tolerate light frost have that stretch to themselves. One spring in ten still has a 28°F night on or after February 26, and one fall in ten sees the first by November 25.

What this means for planting in Portland

In Portland the University of New Hampshire Extension count lands like this, measured from the typical last frost on February 25: lettuce from January 28 to February 4, cabbage on January 28, seed potatoes from February 11 to February 18, then peppers on March 11 and beans from February 25. Peas have no frost-based date in the University of New Hampshire Extension sheet: they go in as soon as the soil thaws.

24 days lie between the typical and late dates in Portland, enough to decide whether you plant tender crops early with a cover ready or wait for a safer spring.

Portland's first frost leaves room for only 32 of the 34 fall crops, counting back NC State Extension's days to harvest and University of Georgia Extension's harvest allowance of 18 days; for the other 2 the last planting day falls before July. The slowest crop that still fits is collard greens, at 118 days, and it has to be planted by July 15 to beat the early date.

Worked example: fall broccoli in Portland

Take fall broccoli in Portland. NC State Extension lists up to 80 days from transplant to harvest, and University of Georgia Extension adds a harvest allowance of 18 days, so the plants need 98 days before the first frost. Counting back from the typical first frost, December 1, the last planting day is August 25. Counting back from the early date, November 10, it is August 4.

21 days separate the two last days, enough that in Portland the earlier one is worth following.

Spring is the other end of the same arithmetic: University of New Hampshire Extension sets cabbage-family transplants out two to four weeks before the last frost, which from February 25 puts cabbage out on January 28.

The weather station behind these dates

2.3 miles south-west of the city's internal point, the station is close but not on top of Portland.

At about 160 feet, it ranks above 22 and below 77 of the 100 stations used for these pages. In NOAA's file the record is marked R, meaning representative.

No elevation is available for Portland in the Census data we saved, so the station's height may or may not match your garden's. Compare nearby stations in the frost dates tool if it does not, and err toward the colder dates.

Portland compared with nearby cities

Here is how Portland, with a last frost on February 25 and a first frost on December 1, compares with the three nearest cities on these pages, the closest being Tacoma, WA at 119 miles.

• Tacoma, WA, 119 miles to the north: last frost March 8, first frost November 14, 250 days frost-free; the last frost is 11 days later than in Portland, and the frost-free season is 30 days shorter than Portland's.
• Seattle, WA (145 miles, north): its last frost comes 11 days after Portland's, and the season runs 21 days shorter. Its typical dates are March 8 and November 23, with 259 days frost-free.
• Spokane, WA lies 288 miles north-east of Portland. Typical last frost April 26, first frost October 15, 170 days between; spring frost lingers 60 days longer than in Portland, and the season runs 110 days shorter.

Next steps for Portland gardeners

The frost dates tool opens on this station and lists every probability date, not just the ones above. From there, the spring planting planner and fall planting planner turn the dates into crop lists for Portland, and the hardiness zone lookup answers what will overwinter.

Looking for another city? The city frost dates index lists every page, grouped by state.

Where these numbers come from

Every frost and freeze date comes from the station's entry in NOAA's U.S. Climate Normals for 1991–2020 (doi:10.25921/4ek7-fk11), with no adjustment, and NOAA's documentation explains what each probability means. The Census Bureau's 2024 Gazetteer places Portland on the map, and its Vintage 2024 estimates, 635,749 people here, decide which cities get a page.

University of New Hampshire Extension, NC State Extension and University of Georgia Extension supply the planting rules; this page only counts them from the station's dates. See how we source every figure for the checks behind them.

NOAA's dates say how often frost has come, not when it will. Check the forecast before planting and keep a cover on hand.