How Often ToPressure Wash.

If you moved here from a drier climate, the surprise usually hits around year two: a driveway or stretch of siding that would’ve stayed clean for years somewhere else is already showing green and black buildup. That’s not a fluke — it’s just what happens in a climate this wet, and it changes how often pressure washing actually needs to happen.

Moss and algae need moisture and shade to establish, and the Portland area supplies both for a good chunk of the year. Concrete and siding that stay damp under tree cover or on a north-facing wall are the first places it shows up, often well before it’s visible anywhere else on the property.

These are starting points, not fixed rules — a shaded, tree-covered lot will need more frequent attention than one that gets full sun most of the day.

Green or black streaking, a slick or slippery feel underfoot on concrete, and visible growth in grout lines or seams are all signs buildup has gone past the cosmetic stage. Waiting too long doesn’t just look worse — established growth is harder and slower to remove than routine buildup, which is part of what drives pricing higher on neglected surfaces compared to ones cleaned on a regular schedule.