Mold is usually created by the growth of filamentous fungi. If the water content is high, these organisms will grow on almost any type of organic matter. While the sight of mold growing on a freshly opened substrate bale may seem worrisome, they are not pathogenic to plants. There are numerous species of fungi, and those found in peat moss are mostly saprophytes, meaning that they only feed on decomposing organic matter. Some of these microorganisms can even have beneficial effects on plant growth.

In unused peat-based growing media that have been stored for a prolonged period, some mold may be seen on the external layer of the mix, just beneath the plastic bag or wrapping. Water can build up in this area of the bale, which generates optimal conditions for fungus development. Mixes with high fertilizer charges or those that are exposed to high temperatures during storage are more at risk to develop mold, but it can occur on almost any peat-based product.

The white mould is Trichoderma. It is a naturally occurring beneficial micro-organism that lives in most soils. Usually you cannot see its presence, but sometimes it appears as white mould on the surface of peat.

Trichoderma is a group of saprophytic fungi, which inhibits the growth of plant pathogenic fungi. It is also used as a commercial biofungicide as it prevents the attacks from plant pathogenic micro-organisms during cultivation. Trichoderma is, therefore, extremely beneficial fungi which naturally protects the substrate from plant pathogens and causes no negative effect to plants.

Yellow or orange powdery like growth on the surface of peat is due toPeziza ostracoderma, commonly called as cinnamon or peat mould. It is another non-harmful but common saprophytic fungi found on peat. Saprophytic fungi live on other fungi in decaying organic material such as peat. They do not live on living plants.

Due to low pH and low oxygen levels that are natural to bogs, plant pathogenic micro-organisms are not present in quality raw material. They have never occurred in analyses. There is no need to sterilise the peat. Heating would kill the beneficial Trichoderma, and on the other hand, sterile growing media would attract harmful fungi and enhance their growth as there would be no micro-organisms, such as Trichoderma, fighting them off.

Sphagnum peat moss contains numerous microorganisms that occur naturally in peat bogs, including the bacteria Bacillus, the actinobacteria Streptomyces, the fungi Penicillium, Trichoderma and Mucor, to name a few. The presence of a healthy community of microorganisms in sphagnum peat moss makes it more difficult for root rot organisms like Fusarium to establish, because the inoffensive saprophytes compete with the pathogens for available resources. Moreover, some species such as Trichoderma and Streptomyces are known to synthetize molecules that are quite effective at suppressing some root rot pathogens though various modes of action.
The microorganism population in peat varies depending on several factors, including the harvesting site. Blond, high quality and less decomposed peat typically has a more diverse and healthy population. It is therefore more susceptible to provide disease suppression.

The mold that can be seen on received  picture is caused by saprophyte fungi, microscopic organisms found in peat bogs that are not pathogenic to plants. They mainly develop on the external layer of peat or growing media, underneath the plastic bag or wrapping, where water tends to accumulate during prolonged storage periods, like it was in container for 2 months.

If you receive a product that has visible mold growing on its surface when you remove the plastic bag or wrapping, do not be alarmed. The product is perfectly safe to use and plant growth will not be affected by these microorganisms. The material can be managed like any other peat moss product you have received:

  • loosen the substrate and mix thoroughly, this will cause the fungus to collapse.
  • add the recommended water to optimize the characteristics of the mix before potting.
  • because fungal growth requires nutrients, the occurrence of saprophytic fungi may result in deficiency of plant available nutrients, nitrogen (N) in particular. Use fertiliser from the very beginning of growing to prevent any deficiencies.

Note that the peat is safe to use – the fungi is not harmful to plants. The adverse effect of saprophytic fungi is purely visual. Moreover, there is no effective fungicide available against them. In dryer conditions the fungus will not become visible, so it shouldn’t reappear during cultivation. To avoid all types of fungi during cultivation, allow the surface of the substrate to dry regularly and reduce relative humidity when possible.