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Graphic of a network of fungi that connect the roots of different plants

How To Help Beneficial Fungi In Your Garden

Without sufficient beneficial microbes on (and in) our bodies, we get sick very fast. It’s the same for plants.

Perhaps the most beneficial fungi for plant health is a group of fungi is called mycorrhizal fungi. This article is about how to maintain your garden to encourage the beneficial fungi in the soil to be as healthy as they can, because they do a lot of work for us in the garden.

Mycorrhizal fungi live in the soil in partnership with plants. The beneficial effects of these fungi are that they:

  Seek out phosphate and other nutrients and then bring them to plants
  Connect many plants together, allowing for nutrient exchange between plants
  Supply water to plants
  Protect plants from fungal diseases and other root-feeding microorganisms
  Improve soil structure, so it’s less compacted, with more spaces for air and water

Here are 10 tips for keeping your soil's beneficial fungi happy!

1. Phosphorus Fertilizer

When plants have ample access to soluble phosphorus (soluble means it dissolves in water, so is easier to take up by plants), they aren’t as reliant on mycorrhizal fungi, so they don’t allow the fungal infection to occur with their roots as much.

That means by using soluble phosphorus fertilizer, we’re interfering with how nature provides plants with phosphorus, so we’ll need to take over the job of the fungi and continue to fertilize our plants every year. Even fresh manure can oversupply phosphorus.

Rock phosphate is okay because it’s insoluble — it actually needs to be worked on by microbes such as these beneficial fungi in order for plants to most effectively use it.

  Don’t use too much, especially chemical phosphorus.

2. Other Fertilizer

Other than phosphorus, over-fertilizing in general can inhibit mycorrhizal fungi, so it’s good to fertilize just a little at a time. Take the fertilizer recommendations from you soil test results and split it up into 2 to 4 applications during the year instead of all at once.

Graphic of hand applying fertilizer to plant

Too much nitrogen seems to be the next big issue after phosphorus, and sulfur is another big one too because it’s anti-microbial. Many soils are deficient in sulfur, but if we use gypsum or potassium sulfate (both contain about 18% sulfur), that’s going to be less damaging to fungi than elemental sulfur (90% sulfur), which is much more soluble.

3. Organic Fertilizer

One reason organic fertilizers are nice is because they tend to either be rock fertilizers (such as rock dust) that are slow-releasing and therefore won’t cause as many problems, or are broad-spectrum biological fertilizers (such as ocean water) that supply just small amounts of many different nutrients and therefore won’t oversupply any one nutrient.

It’s still possible to over-apply organic fertilizers, but they’re more forgiving.

4. Pesticides

The suffix ‘cide’ means to kill. Fungicides kill fungi, so using them can harm mycorrhizal fungi. But so can herbicides, insecticides and other pesticides.

Just spraying a pesticide once isn’t going to knock out your whole fungal network, but repeated applications, especially of certain pesticides such as methyl bromide, will kill most of your microbial soil life. Most countries stopped allowing methyl bromide use years ago, but the U.S. still allows it.

5. Mulch

Graphic of wheelbarrow of mulch in garden

Maintaining a consistent mulch of leaves, straw and perhaps some wood chips will provide protection and habitat for the fungi.

A living mulch (a groundcover or cover crop) is also useful to give beneficial fungi more plants to partner with.

6. Diversity

Mycorrhizal fungi benefit from having other microbes around, including beneficial bacteria, so while compost doesn’t provide the fungi itself, it does support them, as does using compost tea and effective microorganisms.

Plant diversity is also beneficial, which is one reason why crop rotation can be helpful, and why leaving some weeds and wild areas is also helpful.

7. Water

Graphic of man of watering garden

Like us, fungi need water, but they also need air, so if your soil is so wet that there’s not enough air, the fungi will suffer.

But even if your soil is just consistently moist, that’s also an issue because the fungi won’t have any reason to go searching deeper in the soil for moisture. You also face the same issue with plant roots. We want roots and fungi to spread out and go down, so you need to let the soil dry out a little between waterings.

8. Tilling

Tilling, plowing and double digging will slice your fungi up into pieces. It can sometimes be useful to do one of these when you’re first establishing a garden, but in the long run, it’s better to limit them to only when the benefits outweigh the downsides, which may be occasionally, or may be never. Sometimes they’re useful to lightly incorporate a cover crop or control weeds, but otherwise, less soil disturbance is usually better.

9. Other Soil Disturbance

Topsoil removal during construction is devastating to fungi. Compaction is detrimental as well, as is erosion. On a farm, there’s usually more bacteria than fungi in terms of biomass (weight). In a forest, there’s 5, 10, 100, even 1000 times more fungal biomass than bacteria!

The main reasons for this big difference are the lack of tilling/plowing, compaction and erosion in a forest, plus the lack of pesticides being sprayed, and the plant species growing there.

10. Apply Garden Soil Inoculant

There are many types of inoculants. A garden inoculant is anything that adds beneficial microbes to the soil.

Some inoculants are made of Lactobacillus bacteria. You’ve probably heard of these beneficial bacteria in yogurt. In this article, we’ll focus on inoculating legume plants with Rhizobium leguminosarum, a bacteria which fixes nitrogen into the soil.

Rhizobium bacteria are microscopic beneficial organisms that live in the ground. They attach themselves to the roots of bean and pea plants. The plants then develop nodules which house the bacteria. These nodules help feed the plant and other surrounding plants.

Basically, these bacteria form a symbiotic relationship with legume plants that helps the beans and peas get additional nutrients. The bacteria don’t only benefit legumes, because anything you plant near or after your inoculated plants will benefit, too.

Purchasing Inoculant

You can purchase soil inoculates from garden centers or your favorite online store. Johnny’s Seeds offers several varieties. Commercial inoculants are made of bacteria, which multiplies once it is added to the soil.

A little inoculate goes a long way. Five ounces will cover one hundred pounds of seed. Watch the expiration date on the package. Old bacteria will not grow well. Store extra inoculant in a cool, dry location.

Making Your Own Inoculant

You don’t have to buy inoculant. Your garden or nearby wilderness area has many types of bacteria that you can utilize. Growing rhizobium bacteria is a bit more difficult and takes some laboratory equipment. However, you can always make your own starter with different bacteria using things you can find in your area.

Go out into a livestock field or meadow and pull up a legume plant such as clover. If the clover has nodes on the roots you can transport that to your garden to add beneficial bacteria. Make sure you are pulling from a sustainable field that hasn’t been treated with pesticides.

Further Information on Garden Pests:

 Groundhog Facts and Control
 Japanese Beetle, Facts and Control
 How To Get Rid Of Ants
 All About Aphids and Their Control
 Voles — Both the Good and the Bad

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