Sphagnum peat moss

Periodically we receive questions from customers who ask the following about Sphagnum peat moss: Does it contain weed seed?  Could there be plant pathogens in it?  Is peat moss sterilized?  To address these questions, let’s first describe the natural environment where Sphagnum peat moss is found. 

Sphagnum peat moss is a plant that grows in an aquatic, bog environment.  The water and plant debris within a peat bog is unique because it is very acidic (pH of 3.5-4.0), has little oxygen and few mineral nutrients.  Most peat bogs are in southern Canada where the winter temperatures could go down as low as -30°F or lower, depending on the location.  Few greenhouse crops or weeds typically found in greenhouses could tolerate these growing conditions.

Does peat moss contain weed seed that cause problems in crops? 
The short answer is that it is highly doubtful.  Most greenhouse weeds are not indigenous to areas in and around peat bogs, so their seed would not be found in the peat.  Even if a weed is indigenous to the areas near the peat bogs, most will not tolerate the acidic, low nutrient, aquatic bog environment.   Although a peat field that is under harvest is devoid of weeds, it is possible that some weed seed could come from native bog plants around the perimeter of the bog.  However they rarely show up in a greenhouse crop because they will not perform well in non-bog environments.

Are plant pathogen present in peat moss? 
It is rare to find plant pathogens in peat moss that harm greenhouse crops.  Simply put, the crops grown in the greenhouse do not grow in the bog environments, so the pathogen associated with these crops would not be present.  Previous studies have found low populations of pythium spores in peat bogs.   Many of these pythium species are not plant pathogens, but for the few species that are, they are present in such low quantities that they do not pose a problem.  There are also many other native microorganisms found in peat and some, including Trichoderma and certain bacteria, help combat plant pathogens.

Is peat moss sterilized? 
No.  Sphagnum peat moss has many beneficial organisms with almost no plant pathogens or weed seed.  The added cost of sterilizing peat would not be justified.  In fact, more harm can occur if peat moss is sterilized because the natural, beneficial microorganism population would be destroyed.  If these natural organisms are gone, there would be no competition for plant pathogens that would find their way into the growing medium, so plant pathogens can quickly get established and devastate crops.