Treat when it is growing, and dry for a while after
OSU Extension guidance is that moss-control products work best when the moss is actively growing, and that most are short-acting and wash off in the next rain. So you want growing moss and a stretch of dry weather. In the Willamette Valley that points to early spring and early fall dry spells.
A simple calendar
| Time | Good for |
|---|---|
| Late winter to spring | Dealing with the winter's growth. This is the busy season, so book early. |
| Summer | The driest conditions for roof work. Moss is dormant and may look brown. |
| Early fall | Treatment and gutter cleaning before the heavy rain returns. |
| Deep winter | Possible between dry spells, but crews depend on weather. |
Book before you need it
Spring is when most Salem homeowners notice the moss, so crews fill up. Asking early gives you a better choice of dates.
Do not wait for leaks. Moss that has lifted shingles is harder and costlier to fix than moss that is just growing.