Prevention matters on an Edmonds roof more than on most, because the marine moisture that drives moss and algae here is relentless through the cooler months. Once a soft wash has cleared the existing growth, we apply a protective treatment that leaves the shingle surface resistant to new moss, timing it before the wet season when coastal regrowth pressure peaks. For roofs that stay shaded and damp, ridge mounted zinc strips add a passive defense, releasing trace metal ions with each rainfall to slow growth across the slopes below. Together these measures extend the time between full cleanings well beyond what a single treatment would manage, which is meaningful in a microclimate this consistently wet. The approach is shaped by how growth actually behaves near the water rather than by a fixed schedule, addressing the moisture and debris that invite it instead of only the visible result. For Edmonds homeowners, that means a roof that stays clear through the marine season, shingles that retain their protective granules, and a maintenance rhythm suited to the coastal conditions that would otherwise keep moss and algae coming back. We point out the slopes most exposed to fog and shade so each owner knows where regrowth is likeliest and can plan the next visit with confidence rather than waiting for the green to reappear.