When moss takes up residence on roofs or structures, curb appeal isn't all that suffers. Left unchecked, moss can lead to structural damage, and that means extensive home repairs. Heavy moss growth weighs down roofs, displaces shingles and retains moisture that leads to rot and water damage. Patios and walkways become unsightly and unsafe. But eliminating structural moss doesn't have to be difficult.
With the proper approach and effective moss controls, you can overcome destructive moss and take back your structures:
Mosses aren't like other plant pests, so they don't respond to traditional treatments used for common weeds and unwelcome plant growth. Other unwanted plants in your lawn or garden transport nutrients and water – and pesticide treatments – through roots and vascular systems, but mosses are primitive plants that don't have either one. Instead, mosses keep their tissues hydrated by wicking up water from below and soaking it in from above. Retaining moisture is critical to moss survival; without water, mosses can't live. While ordinary weed killers don't get past moss defenses, successful moss treatments target their weakness.
You can't control rain, fog and humidity that keep structural mosses happy and hydrated, but you can interfere with moss's ability to stay moist. Effective structural moss controls, such as those in the Lilly Miller Moss Out! line of moss control products for roofs, walks and structures, breach the protection that helps moss cells retain moisture and cause moss cells to dry out thoroughly and die. With moss dried and dead, you can remove what remains and prevent recurrences.
Moss-fighting products such as economical Lilly Miller Moss Out! Roofs & Walks concentrate work through the power of an active ingredient known as ammoniated soap of fatty acids. These fast-acting, pesticidal soap products coat moss and disrupt its protective layer,1 similar to the way household dishwashing liquids cut through grease. As the fatty acids break through, cells lose moisture quickly, and mosses dry out and die. With results in just a few hours, these pesticidal soaps kill structural moss on roofs, walkways and other surfaces. Reapply annually or whenever new moss growth appears. Unlike many moss killers used on lawns, these products won't stain concrete, pavement, wood or stucco.
Moss controls based on the active ingredient zinc sulfate monohydrate are particularly tough on structural mosses that thrive on roofs and buildings. Non-staining zinc sulfate products, such as the micro-granule Lilly Miller Moss Out! for Roofs and Structures Dry Formula and CORRY'S Moss B Ware products, can be used wet or dry on roofs, patios, sidewalks, bricks and unpainted cement, and won't corrode galvanized gutters. These highly effective controls attach to proteins and organic acids in moss to disrupt growth, injure cell walls and cause moss to dry and die.2 Moss is killed over a three- to five-week period, depending on moss thickness and conditions, but these products also help prevent future moss growth. Oregon State University reports that zinc sulfate moss killers, applied in powder form, have been known to provide effective moss control for up to two years under some circumstances.3
Treating existing moss and taking preventive measures incorporate easily into normal fall or spring cleaning regimens. Effective products have the greatest impact when moss is actively growing during the cool, wet, rainy seasons of spring and fall — and winter, in some moderate climates. Mosses are largely dormant during warm, summer weather.
Achieve maximum results by treating during moss's active season, but when no rainfall is expected for several days. This hits moss at its most vulnerable, without rain to rehydrate its tissues or wash treatments away. For heavy, thick moss, remove as much as possible prior to treatment or the thick layer acts as an umbrella and protects the moss beneath. Always check your product's label for the surface you're treating, before applying the product.
Once dead, light to average moss growth washes away with rains where pitched roofs allow. For heavier growth, non-pitched roofs or flat surfaces, cleaning after treatment is still simple. When practical, remove as much dead moss as possible by hand, broom or rake, and then clean the surface with a cleaner, such as Lilly Miller Moss Out! Heavy Duty Cleaner, which is ideal for use with pressure washers. Always follow product instructions for the intensity of cleaning needed and the type of surface being cleaned.
Prevent moss from returning by treating your roofs and surfaces annually, right before rainy seasons, at the reduced rates for preventive care on your moss control product's label. Take extra steps to lessen the chance of new moss growth. Mosses tend to gather wherever moisture, shade and poor air circulation combine. North-facing surfaces, structures shaded by tree limbs and areas covered with leaf debris may be hardest hit. Prune back overhanging limbs to let more light into problem areas, and keep roofs and surfaces clean of leaf debris to make them less inviting to moss.
If structural moss makes a move on your home, timely, effective controls put an end to unsightly growth and potential damage. With the help of Lilly Miller Moss Out! and CORRY'S Moss B Ware formulations, you can kill structural moss and help your roofs, structures and other surfaces stay safe and moss-free.
Lilly Miller, Moss Out!, and Hose 'N Go are registered trademarks of Central Garden & Pet Company. Corry's and Moss B Ware are registered trademarks of Matson, LLC.
1. North Carolina State University, "Material Fact Sheet Pesticidal Soap"
2. C. Boone, C. Bond, K. Buhl and D. Stone, "Zinc Sulfate General Fact Sheet," National Pesticide Information Center, Oregon State University Extension Services, 2012
3. Oregon State University, "Chemical Moss Control for Roofs, Decks, and Sidewalks"