What Is Mycorrhizal Fungi and Why Is It Important?

Mycorrhizal fungi are a fascinating type of fungi that form symbiotic relationships with 80-90% of plants on earth. But how does that work, exactly?

What is mycorrhizal fungi? Mycorrhizal fungi live in a mutually beneficial relationship with plants. In exchange for sugars that the plant makes during photosynthesis, the mycorrhizae send out long strands called hyphae into the surrounding soil. Hyphae bring moisture and nutrients to the plant in exchange for more sugars. 

You can buy mycorrhizal fungi spores for your vegetable beds or orchard. However, if you’re not careful, you’re going to kill the fungi before they get a chance to help your plants.

This article is going to give you some simple pointers to use and directions on looking after your mycorrhizal fungi. You may be surprised at the difference you see in your yard!

Mycorrhizal Fungi: Definition & Function 

Mycorrhizal fungi may at first sound like a complicated topic only for serious or professional gardeners.

You’ll be happy to know that in reality, the basics really aren’t too hard to understand at all, and applying these beneficial fungi to even a small backyard garden or a few houseplants is surprisingly easy to do and well worth the effort.

What Are Mycorrhizae? 

The terms mycorrhizae and mycorrhizal get mixed up a lot, so let me clarify the definitions for you. 

Mycorrhiza The symbiotic relationship between plants and mycorrhizal fungi 
Mycorrhizae The plural of Mycorrhiza. Multiple relationships between plants and mycorrhizal fungi
Mycorrhizal fungi  A type of fungi that forms symbiotic relationships with plants

Mycorrhizae (symbiotic relationships) are formed when the plant starts pumping exudates into the ground.

Exudates are just sugars that the plant makes during photosynthesis. Eventually, those sugars will reach a fungal spore, which was lying dormant until conditions were right for it to wake up. 

This spore will become a long strand (hyphae) as it eats the sugars, adding more cells to its thin, tube-like body as it makes its way to the source of the food. 

Once the fungal hypha arrives at the plant root, the plant allows it to penetrate its cells, forming arbuscules.

Arbuscules are the site where plants and fungi will exchange nutrients and moisture. (There are also a minority of ecto-mycorrhizal fungi that live outside the root). 

Roles of Mycorrhizae 

This mutually beneficial relationship is vital for plants to thrive.

It is technically possible for plants to grow without mycorrhizal fungi, but they will have to spread their roots far further in search of water and nutrients. 

All that wasted energy takes a toll on the plant, which will be less resilient to disease.

It’s like if you had to walk 10 kilometers (more than 6 miles) to collect water every day.

It’s doable, but all that time and energy would take its toll on your body and prevent you from doing other essential survival tasks. 

Plants that are colonized with mycorrhizal fungi have an overall root network that covers 700 times more soil!

This is because the hyphae grow outwards like a second root system, allowing the plant to access nutrients and water that would usually be way out of range. 

Types of Mycorrhizae 

There are two main types of mycorrhizal relationships, which come from different kinds of fungi. 

  1. Endo-mycorrhizal fungi penetrate the root cells and set up an exchange site called an arbuscule. This is the most common kind and probably the one you would buy from your garden center to add to your yard. 
  2. Ecto-mycorrhizal fungi live near but not inside the plant. This is a minority type of mycorrhizal fungi but can be essential for the healthy growth of trees. 

Benefits of Mycorrhizal Fungi 

Here are some of the main benefits of mycorrhizal fungi:

  1. Provide plants with trace minerals that are otherwise very difficult to get. This makes the food more nutritious for us humans because we will also benefit from those minerals. 
  2. Provide water to plant from a wider soil area. That means you can water your yard less, and it protects your plants from drought. 
  3. Create more structure in the soil, which allows air and water to pass deep into the earth. This also puts carbon dioxide safely back in the ground, helps reduce flood risk, and holds more water during drought. 
  4. Allow plants (particularly trees) to send signals to each other through the fungal network. They warn each other when pests or diseases are present. Trees even send photosynthate (sugars from sunlight) along the networks to younger trees that need a helping hand!

If you find this as fascinating as I do, I highly recommend the book called Mycelium Running. 

Which Plants Benefit From Mycorrhizal Fungi 

Around 80-90% of plants benefit from mycorrhizal fungi. However, the following plants don’t benefit from mycorrhizal fungi:

  • Kale 
  • Broccoli 
  • Cauliflower 
  • Beets
  • Chard
  • Blueberries
  • Radish

The fungi won’t harm them; they just won’t form a relationship with these plants. 

How To Encourage Mycorrhizal Fungi 

Mycorrhizal fungi can lay dormant for many years in the soil. Here are a couple of ways you can nurture them:

Avoid Fungicides and Pesticides 

Whether chemical or organic, fungicides and pesticides are likely to kill your fungal spores. If you have to use a pesticide, try to choose organic options and keep it minimal. 

Keep Conditions Aerobic 

Beneficial fungi do well in aerobic conditions, but the “bad guy” fungi do better without oxygen.

You can keep your yard aerobic by covering any bare soil with mulch or plants; you don’t want any bare ground!

You can also avoid using heavy machinery or driving on your grass and prevent compaction in your beds by never walking in them. 

Avoid Digging or Tilling 

Breaking up the earth also breaks up the fungal hyphae. You can have a thriving veggie garden without digging at all.

It’s a lot less backbreaking, and you’ll find you have fewer weeds every year. (Read this book for more info!)

Don’t Over-Fertilize 

If you fertilize a lot, your plants won’t bother sending out exudates (liquid sugars) for fungi. This means your spores will never wake up.

The problem is, there are 16 essential nutrients for plants. So unless you are providing all 16, you can make the plant less healthy in the long run.

Instead of having a wholesome relationship with fungi, your plant just gets fat on a couple of nutrients.

It’s like feeding your kids candy for every meal. Sure, they will grow, but not in the way you want them to. 

You do want to provide plenty of good compost (learn how here), from which fungi and bacteria will get nutrients for your plants. 

What you shouldn’t do is to just dump nitrogen or phosphorus fertilizers on your veggies. 

How To Use Mycorrhizal Fungi 

There are several ways of using mycorrhizal fungi. If you get the granular kind, it can be sprinkled around the roots of seedlings as you plant them out.

You can also get a soluble type that you use as a soil drench, injection, or foliar spray. Some people even soak their seeds in a mycorrhizal solution. 

Make sure you follow the instructions on the specific type you buy because it will vary from product to product. 

How To Add Mycorrhizal Fungi to Soil

With the packets that I have used, the mycorrhizal spores were mixed with clay to make them easier to use.

I just sprinkled it around the base of plants as they went into the soil, as I found this the easiest and most cost-effective way to go.

It’ll take a good four weeks for these fungi to wake up and form a net around your plant roots, so you’ll have to be patient to see results. 

You can also mix the spores into your potting soil, but it’s best to follow specific instructions with the fungi you buy, as they may have different densities.

Don’t forget you want endo-mycorrhizal fungi for most veggies in your yard, but trees are better with ecto-mycorrhizal fungi. 

You can buy the spores online or increasingly in garden stores. I would personally go for this brand if I were buying online, as it has an excellent reputation. 

Final Thoughts 

Many gardeners take great care to spread phosphorus and nitrogen on their yards, but what about the other 14 essential nutrients that plants need to thrive?

If you want your plants to be healthy, you need to prioritize biology over fertilizer because fungi and bacteria can get nutrients out of any soil, but no plant will thrive on just nitrogen. 

It might feel strange to stop being nutrient focused and start thinking about the microorganisms in your soil, but the proof will be in the eating. 

If someone shouts, “This is the best tomato I’ve ever eaten!” at your next dinner party, mycorrhizal fungi were almost definitely the reason.