Portland, OR Pollen Levels Today

Portland, Oregon's wet, mild maritime climate and lush Willamette Valley setting create one of the most pollen-heavy environments in the United States, with a long and overlapping allergy season stretching from late winter through autumn.

Tree pollen typically kicks things off in February and peaks from March through May, driven by alder, birch, cedar, juniper, ash, oak, cottonwood, and maple—alder in particular is a major early-season trigger across the region.

As trees taper, grass pollen surges from May through July, with the Willamette Valley's commercial grass-seed farms releasing enormous quantities of timothy, orchard grass, ryegrass, bluegrass, and fescue pollen that frequently drifts into the metro area. The late-spring overlap between trees and grasses often produces the year's most intense symptoms.

Weed pollen follows in late summer and fall, led by plantain, sorrel, lamb's quarters, pigweed, sagebrush, and mugwort; ragweed is less dominant here than in the Midwest but still present.

Beyond pollen, Portland's damp winters and abundant shade fuel year-round mold growth (especially Alternaria and Cladosporium), while wildfire smoke, urban dust, and indoor allergens add further strain.

Overall, Portland's allergy profile is defined by prolific grass pollen, an extended tree season, and persistent mold from consistent moisture.