In real life tree trunks and foilage produce patterns of shade and light on the ground. As a result you’ll usually see some spots of dirt alternating with grass rather than a uniform carpet of green. We can reproduce this appearance on bonsai using moss separated by a bit of soil.
To better mimic the mix of grasses growing underneath a tree it helps to use a multiple varieties of moss to give a variety of colors, textures and heights.
Collecting and Cultivating Moss
There are 12,000 species of moss – each with slightly difference appearance. Moss doesn’t have flowers or seeds but instead propagates via an airborne spore – like mushrooms do. The spore germinates and goes through several stages before forming something similar to stems and leaf-like structures, although they aren’t true leaves. Moss absorbs nutrients it needs from the air or the ground.
When moss is dry it can look brown and shriveled – not very interesting. But after a spring shower moss will be wet, green and ready to be collected. You’ll find a lot of varieties growing in cracks of the sidewalk or street. Just scoop it up, along with some of the dirt backing the moss, and put it into a plastic bag. Once home you can grow more or apply directly to your bonsai soil.
There a several ways to cultivate moss using tray or bricks. Collected moss has to be slightly dry out enough to be easy to crumble and cut. Take a shallow container with small drainage holes and put a layer of sand into the bottom and mist until it is damp. Sprinkle crumbled or fine minced moss evenly on the surface of the sand. Mist it until it is damp and place in a dappled shade area and ensure that the top never dries out. It will usually require misting once a day. In a couple weeks you will have a sheet of moss. The other method is using a blender and bricks to start growing moss. Making the “moss-shake” by adding beer, buttermilk, or water with slightly dry moss clump in the blender and blend it to the consistency of thick milkshake. Place the bricks into a tray without drainage holes and fill the container with water; the bricks will act a wick constantly draw water up. Spread the paste on top of the brick and mist daily, in few weeks the moss will grow and eventually will create a solid carpet of moss.
Applying Moss to Bonsai
If you’ve collected moss from a sidewalk or rock there may be a lot of dirt on the bottom side of the moss. While it was helpful to keep the moss damp during transportation, you don’t want to add that to your bonsai because it will cause the moss to be too lumpy. Cut thicker slabs of dirt away with a knife and then gently rub the remaining dirt under water to reduce to 1-2mm thick. Some people also pound the moss clump with a meat tenderizer to break up the dirt. (Using the pointed side seems to work better than the flat side.) The moss will hold together while the dirt will break up. Wash gently to remove.
Now cut the moss into rounded clumps and place on top of your bonsai soil. It will look better if you first apply a thin layer of small (2-4mm akadama particles) on top of the bonsai soil. Leave space between the clumps to allow for growth. Also leave space around the rim of the pot.
Keep in shade for a couple of weeks and mist the moss daily until it is established.
Downsides of Moss
Moss on bonsai soil looks great, but keep it away from the trunk. As you can see in this photo the moss has gotten out of control and is climbing the trunk of this maple. The moss will keep the trunk and (hidden) roots too wet and they can rot.
Removing this type of moss is easy. Use tweezers to grasp the moss and pull it away.
Moss on Pine Trees
In this photo you can see moss starting to grow on the exposed roots of this pine tree. In addition to keeping the roots too wet, the moss can grow underneath the plates of the pine bark and actually cause them to flake off. Because bark plates are a key way of showing age on a pine tree losing them is bad.
To remove moss from roots use a chopstick and gently dig it out. Moss that has gotten underneath bark should be removed by pulling it down using tweezers.
You can also kill off moss with rubbing alcohol. Dip a cotton swab in alcohol and paint the bits you want to die.
Check back every week or so because moss can spread rapidly.
Other Uses of Moss
Although moss is usually used to represent grass around the base of a tree it can also be used in accent plants – such as this moss garden.