Seasonal Window Cleaning Calendar for Portland, OR

Portland’s window-grime cycle isn’t random — it follows the seasons closely enough to plan around. This is a month-by-month reference for what’s actually affecting your windows and when, built on the seven-layer climate cycle covered in our full climate guide.

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The Portland Window-Care Calendar

Months	What’s Happening	Recommended Action
October–November	Rainy season begins; light, repeated rain starts the redeposit cycle; early algae establishes on shaded glass and frames	Good window for a fall cleaning before winter condensation season sets in
December–February	Peak wet season; moss takes hold in tracks and sills where moisture doesn’t dry between rains; interior condensation risk rises on older windows	Homes with heavy tree cover may need a check for track-level moss; watch for condensation-driven mold at sills
March–April	Moss growth accelerates fastest as temperatures rise while moisture stays high; spring pollen begins	Ideal window for moss/algae treatment before growth peaks
May	Pollen season peak; waxy film builds on glass, worse on tree-lined streets	Strong candidate for a spring deep clean — the classic “after rainy season” cleaning window
June–August	Dry season; lowest biological growth activity; wildfire smoke/ash risk begins in late summer depending on the year	Best window for preventive moss/algae treatment and any mineral-etching treatment, since conditions are driest
September	Wildfire ash risk continues into early fall in many years; first fall rains can begin redepositing grime	Clean before ash sits on glass too long if wildfire activity is active in the region that year

Recommended Cleaning Frequency by Home Type

Standard home, moderate tree cover

twice a year — spring (after pollen) and early fall (before wildfire-ash/condensation season)

Heavy tree cover, shaded/north-facing exposure (Sellwood, Alameda, Laurelhurst, Southwest Hills)

quarterly, given faster moss and algae regrowth

Sunny, low-tree-cover lots

can sometimes stretch to once a year without much visible difference

Storefronts and high-traffic commercial glass

weekly to monthly, independent of season, due to constant foot and vehicle traffic film

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Late spring (May, after peak pollen but still within the drier stretch approaching summer) is a strong default for most homes, since it clears the accumulated fall-through-spring grime before the dry season’s preventive-treatment window opens.

Both matter for different reasons — cleaning before wildfire season removes accumulated pollen and rain film so ash doesn’t settle onto an already-dirty surface, and cleaning after (if ash exposure occurred) prevents the alkaline ash from sitting on the glass longer than necessary.

For homes with heavy shade and tree cover specifically, it reflects a real difference in regrowth speed — those conditions regenerate moss and algae faster than a sunnier, more open lot. For lower-tree-cover homes, twice a year is usually sufficient.

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Why Portland Windows Get Dirty Fast · Moss & Algae Removal · Residential Window Cleaning