What is the best time of year to remove moss from a roof?

The best time of year to remove moss from a roof is during late spring to early fall when conditions are mild, but more specifically during dry, overcast weather when moss is actively growing yet the roof is not too hot or slippery. For most climates, late spring, around May, or early fall, around September to October, is ideal. In late spring, moss has had winter moisture to grow and is actively growing, making it more susceptible to moss killers containing potassium salts or zinc sulfate, and you can kill it before summer heat dries it out. Early fall is also excellent because moss regrows during summer shade and moisture, and removing it before winter prevents it from holding moisture against shingles during freeze-thaw cycles, which causes lifting and damage. Avoid removing moss in winter when roofs are slippery and shingles are brittle, and avoid hot summer midday when shingles are soft and easily damaged by foot traffic and chemicals evaporate too quickly. The best conditions are a cool, overcast day with no rain forecast for 24 to 48 hours after application, allowing moss killer to dwell. Never pressure wash moss, as it strips granules. Instead, apply a shingle-safe moss killer, allow it to die over weeks, and then gently sweep dead moss off with a soft broom from ridge downward. After cleaning, consider installing zinc strips for prevention.