The fruiting bodies of ruby bonnets (above left) and coprinellus - species of saprotrophic fungi that grow locally on rotting wood. PHOTOS: MAUREEN HOWARD
You don’t need to use a garden fork or fork out money to benefit the mycorrhizal fungi in your garden, writes Maureen Howard.
With autumn over and mushrooms on the wane, it’s easy to forget the fungal network under our feet in the garden.
Mushrooms are the above-ground fruiting bodies of fungi that comprise a network (called the mycelium) of fine threads (the hyphae) in soil.
Most of the mushrooms we spot in the garden belong to the group of saprotrophic fungi that play a crucial role in breaking down rotting wood.
But many mycorrhizal fungi don’t form mushrooms at all. Instead, they possess an underground “wood wide web” of hyphae that form mutually beneficial relationships with 80% to 90% of all plant species.
In exchange for simple sugars from the plants, these mycorrhizal fungi provide the plants’ roots with water and nutrients such as phosphorus.
Of the few plant families in the world that don’t form mycorrhizal relationships, brassicas and sedges are the ones you’ll most likely find in the garden.
“A good healthy soil will have a whole lot of different fungi” says botanist Prof David Orlovich, who specialises in mycorrhizal fungi associated with native beech from the Nothofagus family.
In addition to benefiting plants, mycorrhizal fungi may benefit the climate too, says Orlovich.
About 75% of terrestrial carbon is stored below ground and the tiny hyphae of mycorrhizal fungi play an essential role according to research published by Heidi-Jane Hawkins and colleagues in 2023.
The cell walls of hyphae are made of chitin - a much tougher form of carbon than plant cellulose. By adding to the structural stability to the soil, the hyphae also break down more slowly in ways that contribute to carbon sequestration.
This is especially the case in native beech forests, says Orlovich.
“You can just push the leaf litter away and you can just see the mycelium growing there.”
The good news is that doing less work in the garden will also benefit fungi. For example: In the lawn, let the weeds grow; in the vegetable patch, interplant instead of monocrop.
“There’s definitely research showing that the more [different] plant species you have in a community the more mycorrhizal fungi you have in a community,” says Orlovich.
Generally, avoid artificial chemicals. Orlovich grows his vegetables without chemicals except for a little lime he uses to prepare the soil for growing zucchini. He also uses animal manures rather than relying on the nutrients the plants receive from mycorrhizae because most vegetables have been selected to grow with manures or chemical fertilisers.
In particular, there’s no need to purchase commercially produced mycorrhizae fungi for the garden - if the soil is healthy and diverse with species “there’s no benefit of [adding] mycorrhizae to good soil”, he says.
Lately, Orlovich has been too busy to get into his garden.
“It is waist-high in nettles, seriously!” he says.
“It has so many weeds I put them on iNaturalist every now and then.”
He plans to get back into the garden again, but in the meantime “it will have lots of arbuscular mycorrhizal fungi’’, if he can “ever get in there and take advantage of them.”
Fungi in the garden
In general, there are four types of fungi found in a typical garden: two mycorrhizae groups (ectomycorrhizal fungi and arbuscular mycorrhizal fungi) and two non-mycorrhizae groups (saprotrophic fungi and parasitic fungi).
Ectomycorrhizal fungi associate with native beech species (Nothofagus), exotic pines and other woody exotic perennials such as European oak and silver birch.
Arbuscular mycorrhizal fungi associate with most of our other native trees, ferns and grasses, as well as most of the plants we grow in our gardens.
Saproptrophic fungi break down the carbon found in twigs and rotting wood.
Parasitic fungi invade their host (e.g., a tree) to obtain nutrients, sometimes even killing it.
- Dr Maureen Howard is the senior education co-ordinator with Town Belt Kaitiaki, and the creator and host of the podcast series Rewilding in Action, with Otago Access Radio.
