The Value of Ground Mosses with Seedling Culture
Mark C. Konrad, M.D.
Under natural conditions, ground mosses and rhododendrons are found thriving together. Mosses play a key role in the formation of soil and the ongoing management of erosion control. Rhododendrons and other seeds find mosses create an ideal site for germination and growth.
Rhododendron seeds falling in the crevices of the moss find the perfect ground cover and natural mulch. The moisture is ideally controlled both above and below the seedlings. The moss also has an important influence in keeping the soil temperature cool, which is very desirable during summer heat. The evaporation of moisture from the moss above ground is likewise helpful in keeping the seedlings cool during hot, dry spells. During the winter, the moss helps moderate the depth of freezing.
Both the ground mosses and rhododendrons are found flourishing in a pH range between 4.5 to 5.5. Where the soil is naturally acid, the pH has been lowered by rainfall, leaching minerals and elements from the mountain slopes and foothills. This process occurs over hundreds of years during soil development.
In an acidic soil, hydrogen ions replace other positively charged ions clinging to negatively charged clay particles, and nutrient ions easily leach out of the soil. Soil pH also affects the solubility of certain nutrient elements. Calcium, for example, increases in solubility (and therefore in its availability to plant roots) as pH increases, whereas iron decreases in availability as pH increases ( Biology , Fourth Edition, Helena Curtis).
It is also interesting to note that phosphate availability in many soils is highest when the soil is neutral or slightly acid, and it declines as the soil becomes either strongly acid or alkaline ( Soil, 1957 Yearbook of Agriculture , U.S. Department of Agriculture, Chapter "pH, Soil Acidity and Plant Growth").
Disk container with rhododendron seedlings growing in haircap moss.
Photo by Mark C. Konrad
Observant specialists in past years noted the connection between ground mosses and rhododendrons and joined the two for improved seedling culture. In 1966, Henry Yates reported great success in using a coating of ground-up moss over his medium filled flats ( Quarterly Bulletin of the American Rhododendron Society , July 1966). The seeds were sewn directly on the surface. His approach was inspired by an earlier article by Guy Nearing entitled "Nature Can Protect Small Seedlings" ( Quarterly Bulletin of the American Rhododendron Society , October 1957). It was stated that the mosses contain an antibiotic substance that protects the small seedlings against most fungi. It might be questioned that the effect is antiseptic rather than antibiotic.
Haircap moss (
Photo by Mark C. Konrad
Mosses do not have water gathering roots but rather hair-like projections called rhizoids which serve as an anchoring mechanism. Moisture is absorbed through above ground structures. Individual cells can absorb water and nutrients directly from the air or by diffusion from nearby cells. The mosses have small leaf-like structures in which photosynthesis takes place.
There are hundreds of different mosses, many of which are difficult to identify. The one I would like to refer to for seedling culture is the haircap moss ( Polytrichum ). The beds are low growing and found extensively in damp, wooded areas.
I have enjoyed the most success with outdoor culture when using flats of wire mesh placed directly on the ground. Burlap is used for shading and small amounts of powdered sulfur is used with watering for insect control. The rhododendrons grow luxuriantly when the medium surface is moss covered.
The easiest way to use the method is to scatter shredded or screened ground moss over the surface of the medium, either before or after transplanting. The shredding can also be done with a pair of scissors. The moss can be used with either indoor or outdoor culture. When used outdoors, the seedlings should be kept at ground level for the moisture and the natural cooling effect.
The advantages of ground moss with rhododendron seedlings have been reviewed. They provide for a living ground cover without roots (and a natural mulch). How much better can it get?
Dr. Konrad, a member of the Great Lakes Chapter, is a frequent contributor to the Journal. His last article, "Modified Nearing Frame Respects Need for Dormancy,' appeared in the spring 1999 issue.