Summer Time Tricks For Treating Moss

Safe & Easy Ways To Get Moss Gone

I like moss. When I first came to the Seattle area, I was delighted to see plush carpets of emerald mosses spreading under big, shady trees. My early taste in garden design was heavily influenced by reading English children’s books, especially the kind that feature secret and/or magical gardens. To this day, I find the look of mossy, overgrown pathways enticing. Who knows where they might lead? After some forty years in the maritime Northwest, I feel that nothing gives a garden a more natural look than mossy pots, mossy trees, mossy un-lawns. I’ve even developed a simple formula to encourage moss on fallen logs or raw new terra cotta containers. (Hint: it involves diluted buttermilk and crumbled bits of your favorite moss.)

However, as a home owner, I’ve had to reconsider my romantic ideals. I still encourage moss instead of lawn where lawns don’t thrive, and I still love mossy woodland paths, but I am no longer captivated by mossy sidewalks or roofs. I’m also disenchanted with the pollen and mold buildup which tends to accumulate on fences, furniture, and house walls. While you can to some degree disguise this build up by painting outbuildings and outdoor furniture a similar color (a not-unpleasing grey green nicely matched by Benjamin Moore Nantucket Grey and/or Sussex Green), it’s better for the long term well being of your real property to power wash the stuff off every few years.

When Romance Fades

In my own case, my romantic vision caused me to allow moss to accumulate on the north side of my roof and to infiltrate the brick pathway to my front door. Actually, I didn’t realize just how mossy the roof had become until an infestation of roof rats encouraged me to remove all the trees that hung over the house. It cost me a pang (and a chunk of change) to remove the trees, even though most of them were misshapen from years of bad pruning (before my time, I need hardly say, right?).

Only one, a graceful Japanese maple, was actually handsome, but it was rapidly outgrowing its position and those arching limbs nearly hit the ground in places when the leaves were wet. Though I didn’t want to admit it, this tree obscured the main entrance and caused some major awkwardness, as when the EMTs coming to help get my tumbled Mom back in bed couldn’t find the front door and squeezed in past my car through the narrow carport to the back door. That tree also overhung the roof, creating perfect conditions for moss mats to form and spread and suddenly romance gave way to practicality. Roofs are not cheap.

Light And Air Are Moss Enemies

Once the trees were gone, it became clear that a lot of silent damage was being done to my infrastructure. Yikes! No more Ms. Nice Gal. Now, sunlight and good air circulation can help keep moss at bay but they rarely make it go away. We started repairs by power washing the deck and house walls. Power washing does a pretty good job of removing pollen, but it’s not very effective for keeping moss away. For one thing, moss develops tiny tenticular rootlets that penetrate wood and brick and stone. You can blast away the top growth, but unless the rootlets are also zapped, the moss will creep back.

Since the sidewalk needed rebuilding by this time, each brick was blasted before replacing it in the new, wider walkway. Even so, within a few months, the green proto mosses were creeping back. To stop them, we spread baking soda heavily over the entire path. After a few days, the mossy bits turned rust colored and could be swept away. However, wet weather always brought the green guys back. The long term solution that works best is to repeat the baking soda treatment every time any hint of green appears. Luckily, baking soda is cheap, especially when bought in hefty 13 pound bags at a box store.

Don’t Knock Baking Soda On Wood

The baking soda treatment also works on wooden decking and stairs, and is especially effective in the warmer, dryer months of summer. Wet down the wood, sprinkle on baking soda generously and let it sit for a few days. When the moss dries out and turns rusty red, sweep away the gunge and repeat as needed. For wooden furniture and stair risers, power washing can be followed up by brushing on a paste of baking soda and a little water with a little bit of dish soap for a sticking agent.

For the past few years, I’ve kept my north-facing roof moss free by sprinkling it with baking soda each summer. Or rather, more truthfully, I have caused younger people to do the sprinkling, since I no longer climb on ladders. The first time they did this, my intrepid crew scrubbed off the thickest moss with stiff brushes that would not harm the composition shingles (as even low-power power washing can do). The thing is, here in the maritime Northwest, rooftops can accumulate not just moss but a clingy matrix of mosses, algae, fungi and lichens. Each has its own gnarly root system and when meshed together, they can be very difficult to remove.

Keep It Safe & Simple

Chemical ‘fixes’ abound, but few are environmentally friendly and some are seriously unwholesome (including bleach, which can stain the roof). For badly infested roofs, the best treatment is a staged series; first, gently scrub off the accumulated growth. Next, brush over the affected areas with the paste of baking soda, water, and dish soap as described above. Let that stay on until rain washes it away. Next summer, repeat the brush on treatment over any areas that still show signs of moss, and sprinkle baking soda anywhere on the rest of the roof that used to have moss, even if you no longer see any.

Unlike most commercial moss killers, baking soda won’t harm garden plants, soil, or water. True, dumping a whole bagful on a given plant won’t be beneficial, but runoff from a roof or deck cleaning job won’t hurt anything. Several readers have asked whether they could safely collect garden-irrigating rainwater off a roof if a toxic moss killer had been used to keep the roof clean. The answer is NO: Rainwater contaminated with zinc, iron or copper should certainly not be used on edible plants. Moss killers based on zinc or copper create toxic runoff that can harm fish and aquatic life (as well as people, in high enough concentrations). Iron solutions are less toxic (though not entirely harmless) but they can permanently stain roof shingles, decks, siding, and lawn furniture, as well as concrete walkways.

Wise Avoidance Techniques

I am also often asked if it’s possible to prevent moss from invading lawns and garden beds in the first place. Well, here in moss heaven, that’s not an easy proposition, but there are some things that will help. Most important are to improve the amount of light and air circulation in the garden, and to change soil from fungal to bacterial domination. Have a skilled arborist prune trees to allow more light and air to reach shady areas. Reorganize beds so pathways are spacious and hedges are divided from beds by service walkways (this really helps when pruning time rolls around). Changing up soil domination is best accomplished by adding compost annually to beds and lawns. Over time, this will balance out soil Ph and help open up compacted or clay-based soils. Finally, don’t over-plant tall shrubs and trees again!

Almost equally simple is this anti-fungicidal solution, which is effective against powdery mildew and molds on plant foliage. It’s also safe to use on edible plants (just rinse well as usual before eating them), and on lawns with red thread or fairy mushroom rings. in addition, this baking soda solution helps prevent early blight on tomatoes, a common problem in the maritime Northwest.

Baking Soda Blend For Plant Problems

2 tablespoons baking soda
1 tablespoon safflower oil
1 gallon water
1/4 teaspoons mild castile liquid soap
(Dr. Bronner’s or similar)

Thoroughly wet down affected foliage/lawn, then apply this mild treatment, shaking the spray container frequently to keep solution from separating. Spray foliage top and bottom (if applicable) or saturate well (lawns). Repeat weekly or as needed. Rinse sprayer in warm, soapy water after each use.