Do not disturb
Doing less really is more when encouraging beneficial fungi activity in your garden, writes
To encourage soil fungi, less is more
Fungi in the garden has long been associated with negative connotations. It’s not without reason: honey fungus, black spot and powdery mildew are all pathogens that attack the living cells of plants – and that’s not good. But to focus on these is disproportionate to the amount of beneficial action fungi undertake. They are fundamental to the garden ecosystem, and although it can seem counterintuitive to say that we need more fungi in our gardens, not less, that is exactly the approach to take.
We’re pretty adept now at understanding the need for enriching and protecting our soils with composts and mulches, but less so on the ability of our plants to access these abundant nutrients. This is where fungi come in. They develop a relationship with roots, called mycorrhiza, which allows plants to take available nutrients in return for sugars. They evolve together in unison, as entwined as bricks and mortar. In nature, this is the bedrock of all growth – and all life.
So, what can we do as gardeners to support and encourage this? Above all, we can take a no-dig approach. When soil is left undisturbed, fungi develop networks of hyphae (their bodies) that take many years to form, connecting plants to one another in complex webs, and aiding each other’s health and survival. The no-dig approach is most important when growing annual crops of fruit and vegies, but it’s also worth avoiding unnecessary digging around, or transplanting of, ornamental plants. Apply loose layers of mulch, and rather than creating mounds of earth around potato plants, use straw or compost. Instead of multiplying perennials through division, try collecting seed or cuttings.
These little changes in our gardening habits will allow fungal hyphae to flourish and reach more nutrients in the soil.
With this approach comes the obvious need for composts and mulches – but with a difference. Traditionally, we make our composts nutrient-rich with lots of nitrogen in the mix and encourage bacteria into action by aerating and subsequently heating the pile. This isn’t a problem, but making fungi-dominant compost needs a different approach. Fungi won’t develop in
high temperatures. They also accumulate in mixes that are more carbon-rich than nitrogen-rich. Fungi prefer damp to dry conditions, but this leads us into trouble: a wet pile that is not aerated is going to be anaerobic (lacking oxygen), which can lead to a foul-smelling mess.
Dr David Johnson and Hui-Chun Su Johnson at California’s Chico State University have devised a solution. Their system, called the Johnson-Su Bioreactor (below right), uses a high ratio of carbon materials – straw, leaves, woodchips and woody stems – as well as manure, grass or food scraps for nitrogen content, and air holes (100mm perforated PVC pipe from the top to the bottom of the pile) to create aerobic, fungi-dominant conditions. Left alone for at least a year, the pile matures at low temperatures, while maintaining relatively high levels of moisture – perfect conditions for fungi to thrive.
There are, of course, simpler but less effective ways of introducing fungi compost and mulches to the garden. I’ve used leaf mould for many years. Although it’s low in nutrient content compared with the Johnson-Su method, left unturned it will create good populations of mycorrhizal fungi. Woodchips will encourage fungi, too, but they take a long time to break down, and possibly only if they are kept damp – hence why they are good for paths or permanent mulch cover.
If we’re to start on a journey to cultivate wild fungi in our gardens, we’ll want to see the fruits of our labour. However, fungi are a mostly subterranean entity, holding their secrets deep within the soil. But if you scratch just below the surface in an area where you’ve introduced fungi-dominant compost or mulches, then you should be able to see the hyphae. They look like fine, marble-white hairs or filaments that spread throughout the soil. If you happen to dig up a plant, look closely at its roots and you should see these stringy, hair-like threads attached. And we know to look out for fungi’s most identifiable feature: mushrooms. Their fruiting bodies release spores to help the fungi multiply and you’ll most likely see them in autumn and after rain.
In the end, this approach is all about protecting and cultivating a wild soil. The more we, as gardeners of a green and natural space, look after and regenerate our soils, the more health and prosperity in the garden we leave behind for future generations. The natural world is suffering and soils are degrading at an alarming rate, but we have the enviable ability to make a tangible difference to this by our action and our methods in our gardening craft.
Matt Rees-Warren is a garden writer and designer, who specialises in ecological gardening methods and practices.