What to do if Mould are Present?

Sometimes, at certain temperatures, water condensates between the peat bale and the plastic wrap, creating conditions conducive to fungal growth. If you notice white or yellow mould when you open the package of peat substrate, there is no reason to worry, it is Trichoderma or Peziza ostracoderma. It is a fungus of saprophytic origin (this means they only feed on decomposing organic matter), that is harmless to humans and plants. These are natural microorganisms that are found in almost all soils. Some of these microorganisms may even have beneficial effects on plant growth.

Sphagnum peat moss contains many microorganisms that occur naturally in peat bogs, such as the bacteria Bacillus, the actinobacteria Streptomyces, the fungi Trichoderma, Penicillium and Mucor. The presence of a healthy community of microorganisms in sphagnum peat moss makes it difficult for root rot organisms such as Fusarium to develop, because the inoffensive saprophytes compete with the pathogens for available resources. In addition, some species such as Trichoderma and Streptomyces synthesize molecules that are quite effective in suppressing some root rot pathogens.

White spots of Trichoderma mould on growing media

Although there is no need to worry about plant safety, we can imagine that you want to limit the growth of fungi. Mould growth is only a visual problem. On top of the growing media fungi do not look nice and sometimes has a bad odor. The fungi usually have a white, yellow, beige, grey or brown colour. This colour is caused by the weft of the fungi that grows at the surface. The colour of the fungi may change during the life cycle.

White mould is Trichoderma – it is a naturally occurring beneficial microorganism that lives in most soils. Usually it’s presence cannot be seen, but sometimes it appears as white mould on the surface of the peat. Trichoderma is a group of saprophytic fungi that inhibit the growth of plant pathogenic fungi. Incidentally, it is also used as a commercial biofungicide because it prevents attacks by plant pathogenic microorganisms during cultivation. Thus, Trichoderma are particularly beneficial fungi that naturally protect the substrate from plant pathogens and do not have a negative effect on plants.

Yellow mould is Peziza Ostracoderma – commonly called cinnamon or peat mould. It is also a harmless 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.

The mould shown in the pictures mainly forms on the outer layer of the growing media, under the plastic bag or wrapping, where water tends to accumulate during long-term storage, which creates optimal conditions for the development of fungi. Mixtures with high amounts of fertilizers or those exposed to high temperatures during storage are more at risk of developing mold, but it can form on almost any peat-based products.

Yellow mould Peziza Ostracoderma on peat based substrate


  • Note that the peat is safe to use – plant growth will not be affected by these microorganisms.
  • If you see fungi in the growing media, we recommend to loosen the compressed material and mix it thoroughly. This will disrupt the growth of fungi.
  • It is not necessary to sterilize or use fungicides, because the mold itself is harmless and there is no fungicide specifically designed to destroy it. In addition, heating would kill the beneficial Trichoderma, and on the other hand, a sterile growing media would attract harmful fungi and promote their growth, as there would be no microorganisms such as Trichoderma to fight them.
  • Once the growing media are taken into use for cultivation, the fungal growth will disappear and should not reappear in subsequent growth stages. However, it is important to note that if the growing media is kept too wet during the crop cycle, the populations of these microorganisms can increase significantly on the surface of the substrate in the pots. This can interfere with the distribution of water and penetration into the mixture. We recommend good irrigation practices, avoid overwatering the growing media and allow it to dry out to a certain extent before applying more water.
  • Ventilate the greenhouse well.


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