What the Fuzz?

Unearthing the Hidden World of ‘Soil Fuzz’: Your Guide to Beneficial Actinomycetes

Organic growers and living soil enthusiasts understand that healthy, fertile soil is alive, teeming with billions of microscopic workers that silently toil to cycle nutrients and sustain plants. The vast majority of this activity occurs beneath the soil surface but, every so often, some of these invisible organisms reveal themselves…

Picture the scene. You’ve transplanted your precious young plants into their final stage Grassroots fabric pots, filled with the best, nutrient-rich, living soil potting mix. Everything is going well until, a week or so later, you notice a peculiar fuzzy growth blanketing the soil surface. Is it a malevolent “mould” straight out of “Stranger Things” or more benign and beneficial mycorrhizae? Searching online does little to quell your concerns and just adds to your confusion. Put simply: is this ‘soil fuzz’ good or bad? Well, worry not fellow organic gardeners. We’re here to help with some savvy soil health tips! Let’s unravel the mysteries of ‘soil fuzz’ and the soil microbiome together!

Okay, So What Exactly is this ‘White Soil Fuzz’?

Many gardeners, especially indoor organic growers, are unnerved by the speed at which this white webbing can sometimes appear, apparently cloaking the soil surface in a fuzzy patchwork. It’s natural to wonder, “Why is this white mould growing on my soil?” Should you panic and start scraping it off or embrace it as a friend? Well, the good news is, this fuzz is most likely not a fungal foe, but more probably a beneficial bacterial friend! Fellow soil lovers, allow us to introduce you to Actinomycetes!

Actinomycetes – Beneficial Soil Bacteria

First things first: Actinomycetes are not fungi; they are threadlike soil bacteria that form fuzzy colonies that are often misleadingly termed ‘mycorrhiza’. The common genus Streptomyces churns through organic matter like tiny wood chippers, releasing earthy aromas. Their hair-like bodies interlace through soil pores, decomposing mulch, leaves, even wood. Like miniature composters, actinomycetes unlock nutrients to feed plants.

Why Does Soil Fuzz Appear?

Actinomycetes thrive on organic inputs such as compost, leaf mulch, wood chips, straw, manure, peat moss, bone meal, blood meal, and feather meal. Amending soil with any of these organic soil amendments helps to feed these hidden helpers.

If you’re looking to rejuvenate your soil, check out our premium organic soil amendment, Life-Cycle, that’s packed full of the highest quality organic nutrition including highly beneficial humic acid and fulvic acid. Life-Cycle’s legendary soil-restoring capabilities are further enhanced by our new liquid seaweed extract, flourish, that provides a range of trace minerals and organic compounds for your actinomycetes to feast upon.

As actinomycetes digest this biological banquet, their filaments emerge, blanketing soil in a living lacework quilt. The fuzz thickens as the bacteria networks expand, but don’t be alarmed. This signals a balanced soil food web at work. It’s perfectly normal to observe an increase in fuzzy actinomycetes growth after top-dressing with an organic amendment or as a result of the breakdown of organic matter from stems and leaves. Other factors like using mulch, such as straw or hay, will contribute to the growth of actinomycetes. It’s all good—it’s just nature’s ingenious way of recycling organic matter into nutrients for the soil.

Check Out The Surprising Benefits of Actinomycetes

Okay, let’s dive into the soil actinomycetes benefits. Beyond recycling nutrients, some other actinomycetes’ talents are just coming to light. They evolved to live in symbiosis with plants, fungi and soil life. Some even produce antibiotics, like the mould that led to penicillin. Over half of human antibiotics originate from these humble soil bacteria!

Is it Healthy Soil Fuzz or Mould?

How can you know that your fuzz is friendly without reaching for a microscope? Colour and density provide your first visual clues. Bright white, sparse fluff signals a stabilizing system. But thick, grey matted fuzz could mean trouble. Don’t worry—the majority of the visible fuzz on healthy soil tends to be the beneficial variety! Different organic inputs can attract different bacteria and fungi with a range of coloured aerial hyphae. Various colours of growth may indicate a different species; Rhizopus, for example, can appear pale-brown to brown, and some green-coloured growth can indicate it’s a species such as Cladosporium, Aspergillus, and Penicillium.

Still unsure? Labs can perform rRNA gene sequencing to test for actinomycetes, but these services come at a significant cost and may be out of reach for hobbyist organic growers.

In the case of actinomycetes, the visible fuzz on the soil surface is a collection of hyphal strands and spores. Streptomyces bacteria are complex actino-bacteria, growing as a network of filaments from which emerge aerial branches bearing chains of spores. They are mostly aerobic, but some can grow anaerobically in low-oxygen environments.

Out of all rhizosphere microbes, actinomycetes (aka actino-bacteria) are considered rather special because of their highly useful traits and apparent affinity for plants. Their filaments and ability to sporulate help them cling strongly to the rhizospheric soil particles (the soil that immediately surrounds the roots) forming a strong bond with the plants. The spore-producing bacteria, which also produce hormones, enzymes and metabolites act directly and indirectly on plants, affording growers a wide range of benefits including the breakdown of organic matter and phosphorus solubilisation, nutrient cycling and the production of siderophores (iron-chelating molecules). Pretty cool stuff!

Remember, beneficial actinomycetes are saprotrophic (decomposers); this extracellular digestion breaks down decaying organic matter. Think of those defoliated leaves you placed under the mulch layer; these will be broken down by saprotrophic microbes into composites such as amino acids, fatty acids and carbohydrates like glucose; all these substances form a great food source for other soil organisms and plants.

Rhizopus is commonly observed under mulch layers and on decaying leaf material, working as a decomposer in the carbon cycle and is a valuable part of breaking down organic material and amendments.
Cladosporium growth can appear to be more of an olive green colour and similar to actinomycetes it is saprophytic, decomposing organic matter and assisting in nutrient cycling
Aspergillus fungi growth can occur as a green mould, another saprophyte, that plays an essential ecological role in recycling environmental carbon and nitrogen.
Penicillium is typically more of a bluish-green colour and some species provide a range of benefits like solubilising phosphorus, producing phytohormones like gibberellic acid and iron chelating agents like siderophores.

This being said, bear in mind there is no sure way to visually identify the exact species and therefore there is no certain way to confirm these bacterial or fungal growths are beneficial. Having this basic understanding of what it could be can help us manage our ecosystems and provide us with a better understanding of why they suddenly appear.

Keeping the Balance in Your Organic Potting Soil

The easiest way to keep your soil ecosystem healthy is to maintain a balance. Observing fuzz come and go is nothing to worry about. If it persists on the soil surface for long periods this may indicate that your soil mix is too rich. Try to avoid top-dressing too many amendments at once as this often can cause a sudden large bloom of fuzz.

If you add fresh plant material onto or under your dry mulch layer, it is less problematic when it decomposes quickly. If you add too much fresh plant material that is slow for the soil organisms to consume, add less. If it hangs around on the soil for over a week you have added too much.

If you have a lot of plant material that you’d like to mulch back into your soil, dry it first so you can store it, then add the dry material as required. Alternatively set up a separate worm bin to consume your plant waste, then use the worm castings.

Ultimately as growers, understanding why things happen can help manage potential issues. We can’t and don’t want to stop the growth of these fuzzy bacteria and fungi. Some are endophytes which means they exist inside the plants growing between the cells! More than just being present, they provide an integral part of the growth stimulation and defence response in plants. Their ability to ‘communicate’ and work as a team through quorum sensing in biofilms is remarkable and indicates how much we still have to learn about how soil microbiology really works.

“It’s incorrect to think of bacteria as these asocial, single cells. They are individual cells, but they act in communities, exactly the way people do.” – Bonnie Bassler, molecular biologist

Further reading

Books on Soil Health