I must admit that it was not the flowers that drew me to Mount Desert Island eight years ago, when I came to interview for the Garden Manager position at the Abby Aldrich Rockefeller Garden. It was the mosses. The carpets of moss that are here today have been slowly developing over the past 30 years. They are now the dominant understory planting along our roads and paths creating tapestries of green. Although the mosses at the Preserve grow naturally on our landscapes, we enhance their growth through our garden maintenance activities.
If you walk in the forests here on Mount Desert Island you will see moss-covered rocks and stream edges. You will see mosses growing on trees, on tree roots, or growing in masses in a low wet area. It is uncommon to see a carpet because the leaf litter from deciduous trees makes it more of a challenge for mosses to grow up through each year. Trees like maples, birches, and oaks shed their leaves each fall. The leaves decompose over time to become soil. Evergreen trees like red spruce, white pine, and balsam fir will shed some of their needles annually as well. The result is that you will tend to see the mosses up high in the forest away from the leaf debris.
Species of moss grow naturally in landscapes all over the world. Here in Maine, there are at least 500 species. They grow in alkaline or acidic conditions and some like moist or more seasonally wet locations.
They do not spread through root systems or seeds like flowering plants, but instead will send up spore capsules, usually when it is wet, and those spores will be carried to new locations by water droplets. The spores will develop into a fuzzy green algae-looking growth on the ground in its first or second year. After that, you will start to see the mature moss forms appear, so it takes time.
This does not sound much different from planting a young perennial, right? The first year the plant does not change much because it is focused on growing roots and trying to keep its above ground growth alive. The second year, you see a bit of growth, but it is really that third year when the root system has finally caught up to its above ground size that you see (weather permitting) its mature size.
With no typical root system, many mosses instead have rhizoids to anchor them to the growing surface. Their nutrients come from the air and water. The nutrients are moved around through capillary action.
Caring for mosses
To best cultivate or care for mosses, I have found it helpful to understand a few things. One, mosses require different maintenance than other plants in your landscape. Two, they are slow to grow from a spore to a mature form and the only way to speed this up is to transplant mosses. Three, to have success transplanting and for the mosses to have longevity in their new landscape, you should be taking them from an environment similar to the one you are planting them into.
The Land & Garden Preserve cares for mosses in all three of our garden landscapes, but there are often different techniques used. I will touch on some of those techniques, but there are two maintenance strategies that are the same at all three gardens - debris removal and irrigation.
Removing debris
Debris removal is at the core of our maintenance practices. Relocating debris that would otherwise naturally occur removes the competition for species of moss that grow on the forest floor.
I will just add here that the leaf, needle, and stick debris is very healthy and vitally important to the health of a forest ecosystem. Does removing it in a few areas cause serious forest health challenges, I am not sure. I can confidently say that it will change the system in some shape or form and will decrease the natural process of soil building from occurring in that area.
At Asticou Azalea Garden the debris is swept off carefully with a broom or picked off by hand, in areas such as the moss corridor at the main entrance off the parking lot and the sand garden viewing area. These techniques work well if you have a small area that you are maintaining, and you and your neighbors appreciate the quietness of this activity compared to leaf blowing. This can be a daily activity especially in the fall when the maples and birches start to drop their leaves.
In October, the garden staff will lay a plastic netting with small holes over the moss cushions, pinning it down with large nails. This keeps the squirrels from digging into the moss cushions to hide their seeds and nuts.
At Thuya Garden and the Abby Aldrich Rockefeller Garden, handheld and backpack blowers are used to push the leaves, needles, and small sticks off larger areas that are carpeted in mosses. When the enclosed gardens are open the work may be done daily along with cleaning debris off the gravel paths.
Outside the enclosed gardens in the less intensively managed portion of the landscape, blowing may be done weekly or just seasonally in the spring and fall. For mosses, seasonal debris removal is enough to eliminate its competition. We practice daily removal for aesthetic reasons. It is possible that daily removal may take away some of the moisture and nutrients the mosses would otherwise get. So, a balance should be found.
The debris is often left onsite out of view of paths and roads to slowly break down naturally. During larger removals in the spring and fall, some of the material will be picked up and piled to create leaf mold or added to compost piles to later be used as soil amendments in the garden beds.
The biggest concern with using blowers is that the more powerful the blower, the more likely that mosses will be displaced, especially the moss species that grow like sheets draped over the tops of granite boulders.
The more powerful blowers move the debris faster allowing you to cover more ground quickly. When we use these tools, we focus on blowing out, not down and we use a sweeping motion from right to left, left to right slowly walking forward, slowly moving the debris. This helps air to skim the top of the mosses, targeting the debris versus the mosses. By displacing some moss plant material, you are helping to spread mosses too, so there is a positive. Some moss species will grow new plants, clones, from broken off leaves. The leaves can grow new anchors or rhizoids and start a whole new plant.
Watering
Irrigation is a way to keep your mosses from dehydrating during drier months of the season. Many of the areas where there are carpets of moss in our gardens have irrigation. At the Preserve, we use an automated pop-up irrigation system with either stationary irrigation heads or rotating irrigation heads. In my opinion, the stationary irrigation heads are more effective for watering mosses because you can run them for a shorter period. In places where we do not have automatic irrigation, we use stand sprinklers and hoses. Remember that mosses growing on the forest floor or rocks do not have roots, so you will make the tree roots very happy by saturating the forest floor with water when irrigating the mosses. For the moss species growing there, they will just need short 8- to 10-minute spurts of water during the driest part of the day, so mid-day ideally.
I like to remind myself that these same moss species grow naturally in our woods without irrigation. They may dehydrate and shrink up a bit without consistent rain or fog, but they will rehydrate when the moisture returns. So, this type of watering is done for aesthetic reasons or for helping an area grow more mosses, not because the mosses will die without it.
Growing mosses
There are a variety of ways to add mosses to your landscape if you are starting from scratch. The slowest way is to let the natural processes do their thing, either by spores in water droplets or bits of moss parts blowing in the wind. At the Preserve, in our dark evergreen woods with little to no soil, this can be done fairly easily. The area is kept free of debris seasonally so that mosses in that area can naturally spread and not be suffocated. For areas where you have more soil and sun, where plants want to grow, you may have to actively remove the debris to keep the space open for mosses to establish.
Growing mosses will take a few years depending on the weather and moss species, especially depending on the weather. It is true that watering does accelerate moss germination, so if you are looking to get moss species to spread into a carpet-like effect, providing some additional water during this time can be helpful (remember this will still take a few years).
There is also the possibility that a species of moss that needs consistent moisture will take hold. This has happened in areas of the Abby Aldrich Rockefeller Garden that are irrigated. The dominant mosses in those areas would typically grow along a streambank and they probably chose to grow there because of the consistent daily irrigation. To reduce the chances of this happening in your landscape you could provide water once or twice a week, to mimic a rain event, but provide a constant daily source of water that a streambank moss would take hold.
Transplanting mosses
Transplanting mosses is a quicker way to achieve a carpet of moss effect in the landscape. This a fairly common practice here on Mount Desert Island where haircap moss species are sold as sod (just like turf grass) and laid in the landscape as a groundcover creating beautiful sweeps of bronzy-green.
You can also look for mosses that are growing in a spot similar to where you want transplant it, with comparable light conditions, moisture, and substrate. Those same conditions should also help you understand how to care for the moss once you have moved it. If it gets slightly more sun in its new spot, for example, you may need to give it some extra water for its first year or two until it is well established but watering it every day may cause it to rot.
Cushion mosses are some of my favorites, such as Leucobryum glaucum. They are commonly seen in in the woods along trails here at the Preserve. The interior of the cushion are the branches. This is a long-lived moss and each year the tips grow a bit more. The trick with moving mosses is removing the entire portion of the cushion or mat all the way down to the substrate that it is growing on.
Once you have it in the new location you should not bury it any more than it was when you found it. For a mat growing moss this may mean that you need to temporarily secure it in place until it grows new rhizoids.
As with any transplanting efforts you should have permission if you are not on your own property or ask your supplier if they have procured the plant material from an appropriate source. Denuding one habitat to create another in my mind defeats the purposes of why we create and maintain beautiful spaces.
As of the writing of this article, much to my disappointment, I have yet to become an expert in moss species identification. I can say that one can make these observations about growing conditions and care without being an expert in moss identification. Much of the work to identify moss to the genus and species level requires microscopes, plant keys, and lots of practice. The good news is that even non-experts can observe and appreciate the differences in growth habits, growing conditions, and the beauty that they bring to any landscape, especially here at the Preserve.
Cassie Banning, Director of Farm & Gardens