Peat Moss

August 1, 2018

By: Ron Kushner

Probably the most prominent and important ingredient of soil less potting mixes, peat moss began in peat bogs 12,000 to 14,000 years ago. After the ice age, glaciers receded and depressions formed that collected precipitation from rain and snow. In Canada, different types of peat formed, depending on the vegetation in the wetland area. Of all the various types, sphagnum moss is the most common.

In Roman times, peat was used as fuel in homes. In countries where timber was scarce, such as Ireland and Scotland, it served as the local source of fuel. In Finland, Russia, Ireland, Sweden and eastern Europe peat is used today on an industrial scale to produce electricity. In North America, peat is used mainly in horticultural applications.

There are more than 335 species of sphagnum around the world with about 16 of those found in Canada. Approximately 5 species are dominant with most bogs limited to only three species. Sphagnum moss is a non-vascular plant (no roots) that grows in acidic water derived from precipitation. As it grows, it leaves behind dead portions, consisting of the cellulose structure of the moss plant to accumulate in the water which we refer to as “peat moss”. The unique structure holds water on the leaves, between the leaves and stems and within the cellular structure. Inversely, air is found where water does not occupy.

The acid pH and low nutrient content of the water combined with the cool northern climate was conducive for the growth of sphagnum moss and the accumulation of peat moss. Over time, the environment of low evaporation, acidic pH and low oxygen limited the decomposition of the vegetation.

Throughout a peat bog, there are different degrees of peat moss decomposition depending upon the depth. If you were to take a cross section of a peat bog from top to bottom, the surface is composed of recently accumulated peat moss that is blond in color and fibrous in texture compared to the lower sections of the bog that contain peat that is further decomposed, dark brown in color and less fibrous.

Raw sphagnum peat moss is graded using the Von Post scale to determine the level of decomposition and humidification. The scale ranges from H1 to H10 with H1 being totally un-decomposed plant material and H10 being completely decomposed. These measurements are based on the color of the peat moss, the fiber content and the color of water squeezed from a sample.

H1 grade raw peat is completely undecomposed peat which when squeezed releases almost clear water. Plant remains are easily identifiable. As we go deeper, H4 sphagnum peat moss is more decomposed and when squeezed releases very muddy dark water. Plant remains are slightly pasty and have lost some of their identifiable features. H10 is completely decomposed peat with no discernible plant structure.

In North America, most peat moss harvested is in the range of H1 to H5. Once the peat moss is harvested, different grades are typically blended to achieve specific physical properties to make them more adequate for the market. H1 peat moss is blond and very fibrous so when used alone as a growing media it shrinks in the container. H5 is dark brown, good as a gardening soil conditioner but it is normally blended since by itself it is too heavy.

Sphagnum peat bogs are found in boreal regions of the northern and southern hemispheres. The combination of an acidic, low-nutrient watery environment and cool temperatures provide ideal conditions for sphagnum moss to grow. The cool temperatures and the absence of oxygen preserve the fibrous, organic layers of peat moss. In Canada, peat bogs cover about 274 million acres, about 13% of the entire country and are present in every province.

Sphagnum peat moss has been used for many years for horticulture purposes for its ability to hold large amounts of air and water, making it an ideal component of propagation media. This is because sphagnum peat moss possesses interconnected cells with thin lignified walls and large cavities that are built-up and prevent the sphagnum cells from collapsing when they dry out. This characteristic provides a capillary system for the peat moss to absorb and transport water easily. As the water evaporates, these cells and cavities fill with air. This situation allows developing plant root systems to easily access oxygen and water.

The bacterial action is reduced in this type of environment which results in a rate of production of plants that exceeds the rate of decomposition. Over time, slowly decomposing vegetation debris accumulates and leads to the development of a peat deposit that could be as deep as 20 feet. In the Canadian peatlands, peat accumulation is about .5 to 1 mm per year or 1/30th of an inch.

When the peat moss is combined with the proper ratio of aggregates, lime, vermiculite, perlite or other ingredients it makes a perfect media for seed starting, rooting of cuttings and seedling development.

Since 1991, the Canadian Sphagnum peat moss industry has funded research with the university of Laval in Quebec to study peat bogs and develop ways to restore peat lands. All producers are in agreement that restoration is essential to maintain the available peat moss for future generations and all practice approved and recommended restoration procedures by law.

For questions or comments: ron@primexgardencenter.com