Moss

General
Moss is a fascinating non-vascular plant. In the context of bonsai, the main use for moss is a very attractive top dressing for bonsai. For many species it is considered requisite to have a moss top dressing for a bonsai display. If you are able to get moss to grow permanently on your bonsai, it does benefit the tree as moss can store excess water up to 20x its weight which buffers the soil from water loss. Another benefit of moss to bonsai is that it keeps the initial top layer of soil from desiccating, thereby allowing surface growth. Depending on the species of moss and growing conditions, it may not be possible to cultivate moss in a bonsai pot all year, so you may need to cultivate the moss separately and dress your tree with it for a show. In our experience in Colorado, Bryum mosses are the best for long term growth on bonsai.

Light
Mosses generally like bright shade, but it is very dependent on the species. Some types like Bryum spp. can withstand some hours of direct sun, but this much light is not necessary. If your moss is to be exposed to direct sunlight, eastern exposure is best and limiting the hours is best. If your moss is to be cultivated under artificial lighting, photoperiod is not important and you would want to follow the same bright shade recommendation. The light requirements of mosses make under benches, trees, and amongst taller plants ideal locations for cultivating moss.

Temperature
Moss varieties offered by Hardy Bonsai are native to Colorado and so are fully cold hardy to zone 5, and can withstand high temperatures of over 100F . During high temperatures, it is very important to shield moss from any direct sunlight.  During winter, it will be beneficial to protect your moss from wind exposure and block the direct line of sight of the moss to the sky. This will limit convection and radiation heat transfer and mimic mosses natural winter habit on the forest floor.  

Humidity/Air Flow
Moss does enjoy high humidity, but it is not necessary for the varieties Hardy Bonsai offers. We grow our mosses outside in southern Colorado where the humidity regularly drops below 10%. Proper airflow is critical for moss. Because of the constant dampness and lower light levels moss enjoys, mold and fungus can take over a moss pot if there is not some air flow present.

Water
Moss performs best when constantly moist, but not waterlogged. Varieties that Hardy Bonsai sells are able to dry out some, but it will set them back. For growing your colony, you should strive to maintain a moist condition. Moss sensitivity to dissolved solids, chlorine, etc. in water is dependent on the species. Bryum is particularly hardy to non-ideal water sources. At Hardy Bonsai, we water our mosses with tap water that comes out at 45 PPM total dissolved solids.

Soil/Pots/Fertilizer
Sterile soil that is moisture retentive is best. Coco-peat and perlite are naturally sterile and this our preferred growing media for moss. We use mostly coco peat with just a touch of perlite to allow for water percolation in our propagation trays (10:1 coco perlite or so). The perlite is not necessary, but helps avoid pot flooding. For growing a colony, large area pots where the moss can be planted somewhat deep are ideal (we typically use 6” pots where the moss is planted with two inches of rim above it). The sides will help protect the moss from high winds, and the large surface area helps increase the humidity a bit. Use a light touch when fertilizing your moss. Mist your moss with a urea-free fertilizer at ¼ the manufactures strength monthly.

Dormancy/Propagation/Troubleshooting

The moss varieties Hardy Bonsai sells do need a winter dormancy, which will happen naturally if left outside. Moss also will go dormant if water stressed, but this water related dormancy is not required and is a survival mechanism. The best way to propagate moss is to divide larger pieces into nickel-sized portions (small clumps will spread faster than large clumps) distributed throughout the pot and let it propagate both through self division and spore production. Ensure that you firmly press your moss into the growing media when propagating it. Moss will turn brown in cultivation primarily in response to too much light, too much fertilizer, inadequate water quality, or drying out. If your moss turns brown, study your growing conditions and focus which of these is most likely happening first.