Mold will grow on almost any organic source, if the humidity is sufficiently high. Molds are generally created by filamentous fungi that are omnipresent in the environment. Each species can have different preferences for certain types of organic food sources, ranging from wood to plant debris. Many of these organisms are used in the food industry to produce wine and cheeses and in the pharmaceutical industry for antibiotic production.
Sphagnum peat moss is no different from any other organic matter, such as bark, compost, coir, mulch, etc. The molds which grow on peat moss and growing media are saprophytic, meaning that they feed on dead plant material and are not pathogenic or harmful to plants or people. These saprophytic molds are found naturally in peat bogs at very low populations, but due to the acidic nature of peat bogs, conditions are not favorable for their development and it results in slow decomposition of the peat moss. However, when peat moss is amended with lime and nutrients, especially nitrogen, this changes the chemistry.
Triggers for Mold Growth: During the crop cycle, if excessive moisture is present and temperature is warm, these favorable conditions allow micro-organisms to propagate in the growing medium. For example, if a crop is kept too wet, certain molds can grow on the surface of the growing medium. Although they are saprophytic, in really severe cases, molds can form a layer on the surface of a growing medium that limits water penetration. To control these molds, reduce irrigations, increase air flow and apply fungicide, if necessary.