The allure of moss begins with an expansive parade of verdant shades — touching our spirits with a sense of serenity. But the benefits are more than sensory. Bryophytes (mosses, liverworts and hornworts) can reduce groundwater contamination, counteract erosion, curtail stormwater runoff and even reduce air pollution. Mosses may be small in size but they offer big options for greening our landscapes.
And mosses can offer year-round green beauty in your garden. As different moss species go through seasonal or reproductive transitions, the nuances of green in the landscape can range from dark, deep green to emerald tones, to neon-chartreuse and olive greens with golden overtones. To add even more delight, their sporophytes (spore prodicers) display intense hues of reds, golds and bronzes.
While many people appreciate mosses in our forests, the historical use of mosses as a horticultural choice in landscaping has been relegated to the grand temple gardens in Kyoto, Japan, tea gardens or the occasional introduction as groundcovers by native-plant enthusiasts. In contrast with moss lovers who encourage natural growth, most landscapers and homeowners go to extremes to eliminate these beneficial plants, considering them weeds. Misunderstandings based upon myths, coupled with a lack of knowledge of bryophytes and their growth habits, permeate the landscape industry, schools of horticulture and public perception.
When speaking of moss, it’s more appropriate to use the plural form, mosses. Mosses are composed of thousands of individual moss plants that grow together in colonies, offering myriad textures and a variety of shapes. In the mountains of Western North Carolina, we have more than 450 types of bryophytes; there are more than 20,000 worldwide. Dating back 450 million years, these hardy plants are not only beautiful, but they provide options for stabilizing steep hillsides and minimizing the effects of rushing stormwater.
What makes bryophytes so special in the plant kingdom? Their unique botanical characteristics reveal implications for diverse landscape applications. Unlike other plants, mosses have no vascular tissues (xylem and phloem, which transport water and nutrients).
Mosses are different in other ways, too:
- They have no roots — only fibrous rhizoids that help them attach to surfaces. These rhizoids don’t feed the plants. While most mosses can be dislodged by hand, rhizoids hold tight to substrates in high winds and don’t blow away.
- Mosses have no flowers or seeds for plant reproduction. Instead, they reproduce through a two-stage cycle that includes spore dispersal via wind and water. In addition, bryophytes can grow asexually from plant fragments.
- Mosses feed through leaves instead of roots. They also have no cuticle, which is the waxy substance that covers leaves of vascular plants.
- They have internal compounds that enable them to be resistant to pests and diseases and to tolerate subfreezing temperatures. No fertilizers, pesticides or herbicides are required for successful growth — a major environmental benefit of earth-friendly mosses.
While advantages of mosses extend beyond beauty, it is their subtlety that captures our hearts and soothes the human spirit. The fact that the growing season continues throughout the entire year is yet another green bonus. Creative moss-features can add interest and dimension to all types of gardens.
Of course, mosses seem to be a natural choice when creating water features (rain gardens, bogs or waterfalls) but they are often overlooked in conceptual designs or haphazardly introduced without following “right moss, right place” guidelines. While a site assessment is beneficial to determine exact mosses, recommendations include: Thuidium, Hypnum, Plagiomnium, Atrichum and Sphagnum.
Mosses add an air of antiquity and permanence even to new construction of hardscapes. Placing mosses between pavers or stones used for patios, paths or permeable driveways is both functional and attractive. Bryophyte types that thrive in either sun or shade include: Ceratodon, Ditrichum, Atrichum, Bryum and Entodon.
Moss lawns provide an option to the American obsession with grass lawns and provide huge benefits to our environment. As mentioned, no chemicals are needed that contaminate our groundwater. Since mosses don’t need to be cut, air pollution from mowers and string trimmers is eliminated. Successful moss lawns often include: Thuidium, Hypnum, Climacium, Mnium, Dicranum and Entodon. When irrigation systems are incorporated or supplemental watering is provided for brief sessions (one to four minutes), mosses will spread faster.
Steep hillsides of clay, gravel or nutrient-poor soil can present challenges in terms of erosion control from the effects of periodic heavy rains. Mulch washes away, and it can be laborious to maintain control of vascular plants. Mosses thrive in fens — a kind of wetland. The botanical ability of moss leaves to absorb and filter water offers a solution. Polytrichum has rhizoids that grow downward that can hold soil in place with surprising strength. Also, Climacium and Thuidium are suggested choices.
As green roofs gain acceptance as a way of greening urban spaces, reducing stormwater runoff and lowering the heat index of buildings, mosses make desirable plant choices. Think about it. Mosses already grow on roofs in our mountain region. It makes sense that they could be intentionally featured on green roofs, particularly if rainwater harvesting is incorporated into the design. The moss green roof at the North Carolina Arboretum in Asheville exemplifies this concept. Installed in 98-degree temperatures in June 2012, this roof has already endured major thunderstorms, winds gusts of more than 60 mph, snow and hail. Featured mosses that live in the direct sun on this innovative green roof include: Hedwigia, Entodon, Polytrichum, Climacium, Leucobryum and Ceratodon, among others. The Arboretum’s moss green roof has the distinction as the first sun-moss green roof in this country!