Using Beneficial Fungi to Improve Garden Health

Powder for mixing beneficial fungus to apply in garden

Applying fungus might seem a little strange to gardeners. We’re used to fighting against fungal disease and other baddies, not inviting it in!  Surprisingly, fungus can also be a friend with garden benefits. Using beneficial fungi in the garden (and other biocontrols) can be a great way to help your garden’s natural defences and boost general health. 

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What are Biocontrols?

Pretty much exactly what you might guess based on that name! Biological control (biocontrol) agents are beneficial organisms that you can apply or introduce to your garden or soil to help control and/or reduce undesirable pests and diseases. Biocontrol agents can include things like:

  • Plants (competitors, bioactivity),
  • Beneficial insects (competitors, predators, and parasites), and
  • Pathogens (bacteria, fungus, and viruses).
Mass companion planting of orange marigolds

Biocontrols for the Home Gardener

Big Ideas in Smaller Spaces

We might think of things like biocontrols as being something that would be used in larger scale growing operations, like the agriculture industry. But they can be used just about anywhere, including in your own home garden. In fact, you might already be using some!

Plants as Biocontrols 

We talk in detail about how different types and combinations of plants can be used to improve the health of your garden in our post on companion planting. In addition to just getting along (or not) with neighbouring plants, they can help condition your soil, crowd out weeds, lure in beneficial bugs, or deter unwanted pests. 

Beneficial Insects

Beneficial insects can act as biocontrols by helping to reduce unwanted pests. Think of the bugs that like to munch on the most common pests, like ladybirds on aphids. This is sometimes used on a large scale as intentional introductions by conservation agencies or farmers.  Most of us home gardeners would probably lean towards letting nature manage those populations, perhaps with the help of some tempting plants. 

Although you’d like to target the enemies, some predators like spiders, mantids, etc. are just as happy snacking on your other more welcome garden guests. And for monarch friendly gardeners, beware that some caterpillar predators and parasites are just as happy to attack your monarchs as unwanted caterpillar nasties.

Inoculants and Biofungicides

Using this form of biocontrol for pests might be a familiar concept for many gardeners. But did you know that you can can also use beneficial pathogens to fight undesirable pathogens? That’s what we’re going to deep dive in this post. 

In my fight against fungal disease in our NZ garden, I’ve started treating soil with beneficial fungi. Yes, fighting fungus with fungus! You might see these products marketed by specific variety or variety grouping, or as mixed content inoculants or biofungicides. I find the latter kind of funny. After all, the content actually includes fungi. 

In addition to helpful varieties of fungi, you can also find biocontrol mixtures with beneficial microbes and bacteria. Healthy soil is filled with organisms, many of which we don’t see or readily appreciate. These types of inoculants are meant to restore or augment natural populations of the garden good guys so they can do their thing. Think of it a bit like a probiotic for your garden. In many cases, the process of things like adding compost naturally boosts the levels. But if you have poor soil or soil that’s recently been treated, perhaps a little boost can help get things back onto a healthier track.

Praying mantis on hydrangea flowers

Prevention is Better than Treatment

Inoculants and biofungicides are most effective as a prevention, not as a cure for dying or diseased plants. They’re best used before any signs of ill-health in your plants, if possible. These biocontrols usually work in a symbiotic manner with the host plants within the garden soil and plant root systems. They colonise the treated soil (and sometimes the plants) and then:

  • Compete with pathogens for nutrients and space;
  • Attack pathogens parasitically;
  • Create compounds that make soil less hospitable to pathogens (antibiosis), and/or
  • Enhance the pathogen resistance, nutrient uptake, and general health of host plants whose roots they colonise.

Sounds good, right? Even better is that many of these products are readily available from garden suppliers and are generally pretty safe and easy to use.

Handful of raised garden bed soil

Selecting and Applying Beneficial Fungi

Product Safety

Good news for gardeners! As noted above, most of the biocontrol products marketed for home use are easy to apply, considered safe, and also comply with organic garden principals. As always, take care and follow product instructions.

Selecting Beneficial Fungi Products

Trichoderma and Mycorrhizae fungi are two of the common beneficial fungi families on the current market for home gardeners. They may be separate or part of a mixed content product. If you’re looking for a product to try, here are a few tips for selection:

  • Shop for your intended use. Are you treating bare soil? Seeds? Seedlings? Established plants?  Trying to recover from or prevent a specific problem?  Some products may be better suited to your specific purposes. 
  • If suitable for your intended use, consider buying a product with a variety grouping (e.g. multiple strains of Trichoderma) or mixed content product to consolidate your treatment cycles.
  • Research reputable local suppliers. 
  • Look for products with listed guaranteed content.
  • Look for stable products with a decent shelf-life.
  • Depending on your personal preferences, look for organically certified products. Many inoculations are made for this target market. Even if your garden isn’t strictly organic, the extra layer of certification is another sign of product assurance.

Our Experiences with Using Beneficial Fungi

Wet Weather Woes

After last year’s unusually wet weather, even some of the very well established plants in our very old heritage home were under serious stress. Fungal disease was taking hold, with blight, dieback, root rot, and general soggy soil. Eek! My usual methods were no match for what nature was dishing out. A new tool was needed in the fight for garden health. Yeah, I know, I said prevention not a cure. But that doesn’t mean you can’t try!

I ruthlessly removed lost causes and cut out the worst affected parts of the plants we hoped to save. I didn’t want to drench or spray with chemical fungicide, if possible, but for the severe case on a sickly mature pseudopanax (pictured below) we cut and then applied a careful localised dose of fungicide. Two of the raised edible garden beds were fully stripped and we solarised the garden soil. The next step was to try fighting to halt any spread and prevent further fungus with fungus.

Experimenting with Friendly Fungus

The biofungicide product came as easy-to-mix powder that can be applied with a watering can. It goes on as an initial inoculation soil drench and periodically thereafter for a refresh. I applied it after the waiting period post-fungicide to my ailing pseudopanax (so far so good). I applied both the biofungicide and a microbe/bacteria inoculant (liquid concentrate) to my solarised garden beds to restore beneficial content to the sterile soil.

The Verdict? 

Since I’m not poking around the roots with a microscope, it’s hard to say with absolute certainty that it is helping. However, since starting use, things have been quite healthy in the root department and growth has flourished. After their emergency dosing, our established plants bounced back better than usual from winter. This was extra exceptional considering we transitioned rapidly from sodden to drought creating a high-stress scenario. It hasn’t helped the arrival of foliage fungus with our recent shift to wet humid weather, but hopefully the plants are a little stronger to fend it off.  I intend to keep using it, and will start our garden at the new house with inoculated soil.

Leaves on a tree with dieback (root rot)

The garden at our new house has heavy clay soil. The use of beneficial fungi has been a key part of arming our plants against the heightened risks that come with soggy winters and baking summers. All major plantings were given an initial inoculation. At-risk varieties have been receiving periodic booster doses. So far so good! We’re one of the few houses not to have lost trees and hedging plants thus far, so I do think it’s helping. Our curious neighbours have also been introduced to my various “witch’s brews”.

Using Beneficial Fungi to Improve Garden Health

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