Hello fellow readers, Each spring, mostly from neat and tidies, the intention to remove moss or lichen from walls and walks comes up. Of course, if they cause a slipping hazard, the desire is justified. But what is it about moss and lichen that folks don’t like? Moss is cute and fuzzy, after all. And lichen is fascinating. And so, I coach to let lichen and moss be.
“Let the lichen and moss be.”
Last week I visited Colleen and Eileen of Lake Mohawk, NJ, who installed a block retaining wall next to their mortared stone wall that’s been there for many, many years. They spoke about sprucing up the stone wall by power washing it and maybe topping it with a cap so it blends better into the new manufactured wall.
I suggested they leave the stone wall be. Let it stand out as the vintage architectural element of the original home, likely built in the early to mid-1930s. Besides, power washing may damage the mortar between the boulders, and the lichen decorating the wall is extraordinary.
Lichens are a fascinating combination of fungus and algae. The algae portion photosynthesizes the sun’s energy into food, supporting the fungus making lichen almost self-sufficient, reliant only on water and air. Think of it as an air plant of sorts (Tillandsia spp.) You know, the trendy alien-looking houseplants that don’t require soil.
Lichen reveals air quality and adds protection.
According to the National Park Service, lichens reveal the air quality in a location. Those sensitive to pollution will discolor or die, and more tolerant species will take over. Colleen and Eileen’s lichen are breathing well and happily thriving.
A while back, I wrote a story about liking lichen (link below) in response to concern over a maple adorned with a tapestry of powdery blue lichen interwoven with moss. Rest assured, the presence of lichen and moss does not indicate a tree’s demise.
Moss and lichen cause no harm; they merely seek a structure to call home. And living hosts, such as trees, benefit from lichen and moss’s added protection barrier.
Unliving hosts may benefit from the added layer too. Although roof cleaners say moss and lichen loosen the granules that provide the color and protect the asphalt and fiberglass in the shingles.
How a mossy roof may be a good thing.
Another client, new in their home, had the moss removed from the roof using a “safe chemical process,” they explain. After which, the roof leaked profusely and resulted in a replacement. While it’s true, it was reaching its life expectancy, but they likely would have had a few more years of the existing roof protected by moss.
Besides, by collecting rainwater from roof runoff into a rain barrel, you gather the benefits of organic material from plant debris, pollen, and bird droppings, offering nutrients to plants every time you water.
Speculation has it moss can damage retaining walls. But the presence of moss is merely evidence of favorable moisture, shade, and acidic pH conditions.
As you expect, those that sell brick, stone, and block wall cleaning services say moss, algae, and lichen can cause damage by discoloring the surface and damaging the wall by loosening mortar. I don’t know; the lake wall has been standing steady for ninety or more years. And the discoloration adds to the charm.
If you insist on a perfect complexion (is there such a thing?), or if algae or moss is causing a fall risk on a walkway, I read using a pressure washer set at 1000 psi or less and a 40-degree fan tip nozzle is relatively safe. Patch holes or cracks before starting and let the patches dry thoroughly to prevent water from seeping into the wall.
But unless there’s a hazard, let lichen and moss be just as Mother Nature beautifully intended.
There’s more to the story you can tune into while on the go:
Link to the National park Service’s story Lichens and Air Quality