Not many gardeners have a neutral opinion when it comes to moss.
Either we love the impossibly green fairyland it evokes on our forest walks and aged garden. Or we hate the layer of slippery moisture it lays over our roof or patio, and the way it crowds out our showpiece lawn. Both camps recount legends of the virtues or evils of moss.
This sets up two typical approaches to gardening with moss — or rather, mosses, as there are many species in any one garden:
1) Totally eradicate them from our property (or make a sport out of trying).
2) Totally embrace them, aspiring to a primeval Northwest rain forest, Japanese-style garden or replica of Tolkien's Middle Earth.
Perhaps there is a more moderate (and easier) option:
3) Discourage mosses where we need to and nurture them where they grow best. Maybe even accept their essential role in a healthy ecosystem.
We live in the Land of Moss. Can we live with it?
Whether we see mosses as friends or foes, it helps to understand them better — how they grow, what they want. True mosses (as opposed to lichens and look-alikes such as Spanish moss or club moss) are bryophytes — among the most primitive land-based plants we can observe. Fossil records show mosses, along with ferns, as some of the earliest plants to colonize land masses. They reproduce by spores, having no flowers, fruits, seeds nor roots. Their simplicity makes them adaptable and has helped them survive for millions of years.
Their growing requirements are different from many of the plants we favor (especially turf grass). So attacking them like a common competing weed may not get us very far for very long.
Contrary to their reputation, mosses are not aggressive — they're opportunistic, as are a host of other garden “pests” that we tend to demonize. These organisms flourish because the growing conditions are better for them than whatever exotic plant we are trying to grow. We might temporarily eliminate them, but if the conditions are the same, they’ll be back.
There are many methods and products to kill mosses in lawns, on roofs, or on paving. One can spend copious amounts of time and money to maintain that spotless roof or perfect moss-free lawn and garden that fits perfectly into a Kentucky or Minnesota landscape, or anyplace except our moist, acidic-soiled, coastal Pacific Northwest.
NO to Mosses?
Where and when do we want to remove or discourage mosses? If we have a garden space with high foot traffic from people or animals (but too shady or moist for turf grass), rootless mosses might be easily scuffed and kicked up, and although they can easily be replanted, it's hard to keep the carpet looking good. We might look into redesigning our site, moving the high traffic zone to a sunnier spot (if we have it) where the grass might do better. Or we might consider substituting other shade-loving groundcover plants, many of which tolerate at least moderate foot traffic.
On any paved surface where people walk, including wood decks and steps, mosses and their associates (namely algae and molds which thrive in moist settings) can cause serious slipping hazards. Build-up of mosses on sloped roofs can be a concern for anyone needing to walk them for maintenance.
Note: there is much debate over whether mosses actually damage roof surfaces (especially wood shakes), or whether power washing and other removal processes, or prolonged exposure to sunlight, do most of the damage. Mosses are inaccurately blamed for forcing gaps and cavities in shingles (moss tissue lacks the structure to do so). But they can colonize those gaps and hold moisture, which can speed the decay of certain roof materials.
How to discourage them
So if you want to eliminate or discourage mosses, the long-term goals are to reduce the shade, moisture and acidity.
For the lawn, ferrous (iron) sulfate as a fertilizer supplement will kill what mosses are there now. Dolomite lime applied twice a year will help reduce the acidity and thus discourage future moss growth. Although, if shade and drainage are still factors, it might not totally prevent them.
If you have chronically wet soil, gradually adding compost and/or sand, regrading to divert runoff, or installing subsurface drain lines can help. If your lawn is shaded by trees, thinning overhead tree branches (if feasible) can make quite a difference.
March is a prime month to put down anti-moss treatments on lawns. Swansons' care sheet on controlling moss in lawns can tell you more.
For built surfaces, physical removal followed by an application of bleach with some dishwashing liquid, is a common remedy. Others include copper or zinc sulfate or potassium salts, such as Lilly Miller Moss Out! and Safer Brand Moss & Algae Killer & Surface Cleaner. These surface treatments can be toxic to nearby plants or groundwater, so take preventative care and follow label directions.
Northwest garden writer Ann Lovejoy is an advocate of using baking soda (which lowers acidity), alone or in other combinations, for a plant-friendly treatment for mosses or algae on both hard surfaces and plants.
YES to Mosses?
Face it: when it's winter and you need a healthy dose of the color green, few plants match the mosses for their glowing renditions. The rainy season is their time to shine. The best way to appreciate them is a walk or hike outdoors, particularly in a park or natural area. The ultimate experience would be a pilgrimage to the Hoh Rain Forest in Olympic National Park. But there are likely magnificent examples of mossy forest right in your neighborhood.
They serve many ecological and practical functions, such as slowing water runoff with their sponge-like nature, and serving as natural insulation. The current green roof trend incorporates these functions. Although most green roof systems are designed for full sun and drought-tolerant plant schemes, there are systems which specifically incorporate mosses.
How to encourage them
If you wish to foster and encourage mosses in your own garden, provide the right conditions — shade, moisture and a substrate they like to grow on — then be patient. They do best on mineral surfaces such as rocks, concrete, compact soils, even clay. Overly mulchy soil is not so friendly. Again, try to avoid areas with a lot of foot traffic. Different species will colonize different substrates.
Transplanting moss plugs from elsewhere might work if the conditions are very similar to their original site, but the best long-term method is to provide the setting, keep competing plants away, and wait. It may take a season, a year or two, or more, but if moss likes the space, it will come.
There is anecdotal evidence that a mix of moss mixed in a blender with buttermilk or egg whites (primarily to help bond the mixture to a surface) can give you a head start in growing moss. But most experts suggest simply providing the conditions for the mosses to colonize naturally.
And remember, stationary surfaces only: "A Rolling Stone Gathers No Moss." Go figure.
If reading this article has suddenly made you a serious mossophile and you would to like to know a whole lot more, here are two comprehensive and entertaining books:
Moss Gardening - George Schenk
Gathering Moss - Robin Wall Kimmerer
We at Swansons are always here to help you find information and advice for dealing with garden mysteries such as moss. Search this website for past blog posts and care sheets, or post your questions on Facebook, Twitter or Instagram and include the hashtag #heyswansons. We're listening!