Mold. Even the word sounds unpleasant. But don’t let mold’s negative connotation fool you. When it comes to gardening, it’s a sign of life.

A Note on the Mission of PittMoss

At PittMoss our mission is to make the best soil amendments and blends on the market. For us, superior results and organic, sustainable approaches to higher yields go together like water and seeds. However, when consumers discover mold in PittMoss products, they often wonder whether this will jeopardize their crops.

To start dispelling the antiquated myths on mold, we’re going to dig into some of the incredible biological benefits of having a healthy dose of it in your soil. Furthermore, we’ll discuss what consumers might find in PittMoss products and alleviate any concerns as to the presence of mold or fungi.

Explaining the Wonderful World of Fungi

The spores that produce mold, or fungi, are underappreciated partners in the garden. In fact, to some degree, they’re present in every common organic gardening mix, from peat moss to bark. When certain conditions are met, spores produce fruiting bodies, like mold.

Many traditional gardening products are treated to stop this growth and improve the aesthetics of their yield. But like many things in life, it’s not just about looks.

For instance, PittMoss is purposefully produced to encourage natural, sustainable, organic growth. Because of our desire to keep the purity of our potting mix as high as possible, we do not add chemicals to our products. In fact, if left in a warm, humid environment, PittMoss will activate biological activity. This activity is perfectly normal and natural.

The Origin of Mold

Mold comes from an ancient group of simple plants called "hyphomycetes" (say that five times fast). It is these fungi that scientists consider foundational to our natural world. Don't believe us? Check out this TED Talk.

Organic gardeners can attest to the fact that gardening with "living soil" is the ideal environment for plants. In the book Soil Microbiology and Biochemistry, researchers E.A. Paul and F.E. Clack wrote, “Soil organisms show their greatest diversity of species and usually their largest populations in productive soils. The size of the microbial biomass usually shows direct correlation with the amount of plant growth.”

If healthy plants aren’t enough, know that the chemicals used to eliminate microbes leach into our water system. This is hugely problematic, as it is widely accepted that pesticide exposure is linked to a litany of health problems, such as birth defects and reproductive dysfunction, autism and learning disabilities, and a multitude of diseases such as cancer and Parkinsons. This is why landscaping companies recommend keeping children and pets off of lawns after they've applied fertilizer.

A Breakdown of Microbes

A quality growing mix should support a full array of beneficial soil microbes. These “friends in the soil” provide for the availability and absorption of essential plant nutrients. They also help to fight root diseases and break down toxins.

In general terms, these microbial workers are classified as:

  • Bacteria
  • Fungi
  • Actinomycetes
  • Algae


Bacteria are microscopic single-celled microorganisms found in growing media, native soil, and compost. They are the most prolific microbial. Bacteria produce enzymes that dissolve and transform minerals and through this process makes nutrients more available to plants. The nitrogen converting bacteria nitrosomonas and nitrobacter are the most noteworthy.


Fungi are primitive plants that typically form multi-celled filaments in growing mix. These filaments form a network called mycelium that grows in the media.

Many fungi grow in association with plant roots and are called mycorrhizae fungi. Like most fungi they serve to decompose organic material and make nutrients available to plants, but the mycorrhizae also help plants absorb nutrients.

Some common families of fungi include ascomycetes, basidiomycetes, trichodermas, and zygomycetes. When conditions are optimal, they develop fruiting bodies which produce white or tan growth on the surface of a potting/planting mix. The spores and surface mycelium are commonly referred to as mold.


With regard to size and complexity, Actinomycetes are in between bacteria and fungi. They form long chains of cells within the growing media. They typically give soil that familiar earthy or musty smell. Actinomycetes often have anti-bacterial and disease-fighting properties. Some common families of actinomycetes include micromonospora, thermo actinomycetes, and streptomycetes which are sources of the familiar antibiotic streptomycin. The fruiting bodies are like tiny mushrooms or puffballs.


Algae are simple plants that grow within and on the surface of nutrient-rich soil and growing media. They are the most widely distributed of all green plants. Sometimes called cyanobacteria, they are primarily water plants and develop where high levels of water or very high humidity are present.

Blue-green algae are the type that commonly grows on the surface of a moist growing mix. Algae cause no harm to plants but is an indicator of conditions that are often excessively humid and wet. These conditions can foster other undesirable infestations of insects and pests.

Biological Activity Seen in PittMoss

The Fungal Mat (mycelium) of zygomycete is a blend of 60% PittMoss Prime Soil Amendment, 30% sphagnum, and 10% perlite. This fungus works to make components in the growing mix more soluble, which allows for easier plant absorption.

fungal matt- microbial development seen in PittMoss

Basidiomycete species (spp.) fruiting (sporulating) bodies on the surface of a blend containing 50% PittMoss Prime Soil Amendment. They are also often considered “Higher Fungi.” They are often associated with root systems and act as an ectomycorrhiza. They are known to enhance the availability of nutrients and nutrient absorption.

Composting is enhanced by the exceptional microbiological activity of PittMoss. This activity is demonstrated in the photo of a pile as seen below. At a depth of about 12” or deeper, the composting fungi can be seen (bottom half of photo) as a white fungal mycelial growth. It was clearly present after about 14 days in a composting pile.

Microorganisms such as trichoderma spp., ascomycete spp., basidiomycete spp., and zygomycetes spp. release enzymes that help to breakdown the substrate materials, making them much more available to plants.

composting improves with PittMoss

Ascomycetes spp. These fruiting (sporulating) bodies are growing on PittMoss—they are often considered “Higher Fungi” and grow within soil and on or near root surfaces producing mycorrhizal associations that increase nutrient solubility and absorption.

A Conversation About PittMoss

So if all of this biological activity is good, is it bad if I do not see any mold?

Whether you can see the activity or not depends on a variety of environmental conditions. Nonetheless, these microorganisms will always be found in gardening blends even if they do not become visible.

This all sounds good, but I really want to avoid seeing any microbial growth.

Managing the environment will greatly reduce the occurrence of fruiting bodies. If PittMoss is stored in a cool, dry space with available air circulation (for example, leaving the bag slightly open), mold is unlikely to occur.

Should I Expect Mold in my Product?

More often than not, you will not see any visible growth. The microbes produce fruiting bodies when they are not properly stored (see the previous question). Also, mold will not remain. In fact, after the first bloom any subsequent growth will be minimal.

If I see mold in my mix, what do I do?

At PittMoss, we recommend simply mixing it up with the rest of the product. It should integrate nicely back into the soil.

Is this the same thing as a "living soil"?

Yes! The idea behind a living soil is that the nutrients plants need to grow are provided through naturally occurring soil microbiology. Just think: plants grow naturally without the need for any additional fertilizer! That is because these soils are teeming with beneficial microbes that provide the plants with all the nutrients they need.