At Moss And Stone Gardens, we are often asked about the type of containers best used for growing moss. As you consider the container or substrate selection for your moss dish, please keep the following in mind.
In – plastics, ceramics, seasoned concrete, stone, wood, soil, fabric or glass.
Out – galvanized or zinc plated metals, copper, pressure treated lumber, chemically unstable materials.
Even though mosses don’t have a root system to draw nutrients or liquids from substrates they are growing on, they are still capable of conduction. This means that direct contact with moisture, which is also in contact with a substrate or material, can transmit dissolved particles to the moss. One of the things mosses are sensitive to is heavy metals and some chemicals.
I have observed a healthy and spreading carpet of moss, stop in its tracks, as it approaches the drip line of a deck constructed with pressure treated wood. When water comes into contact with the pressure treated wood, some of the chromated copper arsenic will leach into the water and be dispersed. This will have negative effects on any moss that is in contact with this contaminated water.
The same effect can be observed with other materials like zinc, which is attached in strips on roofs to retard moss growth. Having said that, I have also observed moss grow on top of, or over pressure treated wood. Admittedly it was always decades old pressure treated wood and not new. However, there is a difference, in terms of the moss being “upstream” from the contamination source, growing on top of pressure treated wood, is a little different than growing beneath it.
To investigate further, mosses living on top of soil that is in a pressure treated planter will fair better than ones planted at the foot of the same container. They are buffered by the soil and basically, upstream from the water that contacts the pressure treated wood.
It is also possible to have soil in a zinc coated container with mosses growing on the soil, but there will certainly be a zone of peril where soil stops and zinc begins.
In a container using an inappropriate material for mosses, good draining soil and drainage holes would be essential to keep the mosses downstream of contaminants.
Damage to mosses from zinc or pressure treated wood may not be visible for weeks or more depending on the species, water volume and contamination levels, the metabolism rates of mosses are very slow and so visual evidence of damage takes time.
In summary, it’s best to stay on the save side and use what’s in for moss — plastics, ceramics, seasoned concrete, stone, wood, soil, fabric, or glass.