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Cannabis,  Compost & Soil Health

The Benefits of Using Mycorrhizae in the Garden

Last Updated on May 15, 2023

When it comes to maintaining a healthy and productive organic garden, there is a lot more happening than meets the eye! In addition to the obvious elements (sun, soil, plants, and water) there is a dynamic network of living things that work synergistically within the soil to help plants thrive. Critters and microscopic organisms decompose organic matter, transform nutrients and minerals, and create various reactions that contribute to overall soil fertility. One of the key players in this essential ‘soil food web’ is mycorrhizae – something we routinely add to our garden soil!  

Read along to learn all about mycorrhizae. This article will cover what it is, how to use it in the garden, and most importantly, the benefits mycorrhizae provides plants. Spoiler alert: it will help your plants grow larger and healthier than ever! We’ve been using mycorrhizae in our garden for many years now, ever since Aaron’s dad turned us on to it. Even if you’re not a hardcore soil nerd, I bet you’ll find this information fascinating!

What is Mycorrhizae?

When you break it down, the word “mycor-rhiza” literally means “fungus-root”. Mycorrhizae is a form of beneficial fungus; one that cannot live without being connected to plant roots. Yet the connection isn’t just about helping the fungi survive! Together, they form a symbiotic relationship that offers outstanding benefits to the host plant as well, such as increased nutrient uptake, added resilience to disease or stress, and higher yields. We’ll talk about the benefits of mycorrhizae in more detail below. 

Over 95% of the world’s plants form beneficial associations with mycorrhizal fungi. Some types colonize on the surface of plant roots only, known as ecto-mycorrhizae. These fungi bond with select woody trees like conifers, hazelnuts, and pecans. In contrast, endo-mycorrhizae penetrate the root cells to become a part of the root system itself. They’re also far more prevalent. 80 to 85% of edible garden crops, fruit trees, flowers, herbaceous plants, and ornamentals make associations with endo-mycorrhizae, so that’s the type you’ll find in mycorrhizal products made for home gardens.

A pine seedling rootball is shown from the soil below. Its rootball is large and expansive, more than 3 or 4 times the height of the seedling itself.
A pine seedling roots flush with mycorrhizal fungi, allowing the plant to obtain nutrients from a bigger volume of soil. Image from David Read, author of Mycorrhizal Symbiosis.

What does mycorrhizae do?

After colonizing plant roots, mycorrhizae acts like an extension of the plant’s root system and can increase the absorptive surface area of roots by up to 700 times! Imagine millions of little straws and fingers now available to more deeply and efficiently access valuable resources within the soil – including water, nutrients, and even air.

Furthermore, mycorrhizal fungi release enzymes that help to ‘unlock’ and dissolve essential nutrients within the soil. That reaction makes those nutrients more bioavailable for plants to easily utilize, including phosphorus, iron, and other minerals. Keep in mind that mycorrhizae isn’t a fertilizer however, so it will only help the plant use nutrients that are present in the soil (albeit better) – so you still need to routinely amend soil with compost and organic fertilizers. Last but not least, mycorrhizal fungi form intricate webs that capture and store excess nutrients in the soil for later use. This enhances soil fertility long-term.

So, what do the fungi get out of all this good samaritan work? The answer is food. As mycorrhizae helps plants to better utilize nutrients for growth and photosynthesis above-ground, the plants send sugars back down to their roots to nourish the fungi. Everyone wins! 

A diagram illustration showing a mushroom growing in the soil next to a tree and its roots. Below the soil line shows the roots from the fungus exchanging water and mineral nutrients to the tree for photosynthesis products in the form of carbohydrates for the fungus.

Benefits of Using Mycorrhizae

Due to the mutually beneficial exchanges that occur between mycorrhizal fungi and plant roots (e.g. increased nutrient uptake), studies show that mycorrhizae offers plants the following benefits:

  • Promotes larger plant growth and healthier, deeper dark green foliage.
  • Leads to greater flower and fruit production (more and/or larger). For farmers, higher yields also means higher income. 
  • Enhanced resilience to stress, heat, and other environmental changes.
  • Improved water uptake, leading to increased drought-resistance and less water demand for the plant. 
  • Lessens the risk of transplant shock, such as when planting new trees or moving indoor-raised seedlings outside.
  • Increases plant disease resistance by promoting overall improved plant health. Also, when plant roots are colonized or coated with mycorrhizal fungi, it limits access to the roots by other harmful pests, fungi, or diseases. For instance, studies show that plant roots colonized by mycorrhizae have added protection against parasitic root-knot nematodes and root-chewing insects!
  • Reduces the need for fertilizer inputs (and associated costs).
  • Decreases the accumulation and residual levels of toxic contaminants in crops, such as persistent organic pollutants (POPs), which plants typically readily absorb in their roots and tissues.
  • Naturally improves soil structure, fertility, and promotes a healthy living soil food web.

Sound too good to be true? Check out the photos of side-by-side grow trials below. The plants were treated exactly the same, with the exception of one being inoculated with Plant Success mycorrhizae – the larger plant in every photo!

A person on each side of the image is holding a small fabric pot with a basil plant in each pot. The plant on the left is almost twice the height and width of the plant on the right.
Basil inoculated with mycorrhizae (left) versus not
Two marigold plants are shown, each in its own fabric grow bag. The plant on the left is much larger, almost twice the size in height and width and more flowers than the one on the right.
Marigolds inoculated with mycorrhizae (left) versus not
A two image collage, the first image shows two eggplant plants, both in its own fabric grow bag and the plant on the right is twice the other plants height and width with more flowers. The second image shows two bean plants, each in its own grow bag. The plant on the right is more than twice the size and width of the other plant with many more flowers as well.
Eggplant and beans inoculated with mycorrhizae (right) versus not. Side-by-side grow trial images courtesy of Plant Success Organics

Plants that Benefit from Mycorrhizae

Nearly all plant species benefit from mycorrhizal associations! Mycorrhizae’s ability to make phosphorus more bioavailable is especially valuable for flowering and fruiting horticultural crops like tomatoes, peppers, squash, cucumbers, eggplant, beans, cannabis, berries, fruit trees, and more. It will also help your ornamental flowers and shrubs thrive, including both annuals and perennials. Beyond flowers and fruit, mycorrhizae promotes more vigorous growth in herbs, lettuce, potatoes, carrots, asparagus, garlic, and onions as well. 

The brassica plant family is among the small number of plants that do not form mycorrhizal associations. Meaning, your broccoli, cabbage, turnips or radishes will not benefit from mycorrhizae – but it also will not harm them!

An early summer harvest displayed in an artistic manner. Green and yellow summer squash, yellow and red tomatoes, apples, rosemary sprigs, garlic bulbs, various varieties of green beans, kale leaves, chard leaves, calendula flowers, avocados, and chiles make up the assortment that is compiled on a large, flat wooden board.
A late spring harvest from our garden. Nearly every one of these plants forms beneficial mycorrhizal associations to boost growth – including apples, tomatoes, squash, peppers, beans, avocados, berries, garlic, flowers, herbs, and more (with the exception of the kale, a member of the brassica family)

How to Use Mycorrhizae in the Garden

Mycorrhizae should naturally be present in healthy, organic soil to some degree. Using organic gardening techniques such as compost, compost teas, cover crops, mulch, or no-till methods all foster a rich and diverse living soil food web! Harsh chemical fertilizers, pesticides and herbicides make soil sterile and inhospitable to all living things – including the good guys. 

However, it can take a long time to develop a robust population of mycorrhizal fungi in the average home garden, especially in newly-established gardens. Also, the native populations of fungi can vary drastically from season to season or bed to bed. Therefore, the best way to guarantee your plants reap the rewards of beneficial fungi is to inoculate your garden with mycorrhizae

  • One option is to sprinkle granular mycorrhizae directly on the root ball or in the planting hole when transplanting new plants into the garden or into a larger container. See the photos below. Water the soil well after application and planting!
  • Another awesome way to add mycorrhizae to soil is to mix up a water-soluble mycorrhizae product and water it in. You can do this any time – be it right after transplanting, or to boost established plants later (e.g. fruit trees or shrubs). If you direct-sow seeds right in your garden (such as beans, peas, or garlic), wait to water them with mycorrhizae until they’re at least several weeks old and have developed a couple sets of ‘true leaves’ – which means they’ll have some roots developed by then too!
  • No matter which method you choose, keep in mind the fungi need to come in direct contact with living roots as soon as possible in order to survive. For this reason, always apply mycorrhizae immediately around the plant’s root system. They can’t travel in search of roots. 
  • Again, remember that mycorrhizae isn’t a fertilizer – it simply helps plants make better use of nutrients in the soil. So, be sure to routinely amend your garden with compost and mild, organic fertilizer too!

Related: Transplanting Seedlings Outside: Tips for Success and How to Amend & Fertilize Garden Beds Between Seasons

A 1/2 teaspoon measurement is full of granular mycorrhizae, below lies a tomato seedling rootball, a trowel, and a garden glove atop a bed of garden soil.
Option 1: Add granular mycorrhizae around the inside walls or bottom of a planting hole, such as when transplanting new seedlings into a garden bed, or planting fruit trees and shrubs.
A tomato seedlings rootball is shown that has been sprinkled with granular mycorrhizae that resembles crushed eggshells. The roots are white and fibrous.
Option 2: Sprinkle granular mycorrhizae directly on to the root ball.
A watering can is being used to water a tomato seedling transplant in a raised garden bed with water soluble mycorrhizae. The background is the border of the yard which contains nasturtium, salvia, fig tree, and the lower limbs and leafs from an avocado tree.
And option 3: Use a water-soluble mycorrhizal inoculant to water freshly transplanted plants (or established plants).

Our Favorite Mycorrhizal Inoculants

There are a number of mycorrhizal products available on the market. We personally love and use the granular and water-soluble mycorrhizae inoculants from Plant Success Organics. They’re one of the most established and reputable brands, and offer high-quality, effective products that are OMRI-certified for organic gardening. I also love that they add beneficial bacteria to their products to further support the soil food web. Bacteria play a similarly significant role in plant health. In a nutshell, think of them as pre- and probiotics for roots, and roots as the gastrointestinal system of plants. There is a direct link between the human gut, probiotics, and overall improved health outcomes – and plants are no different! (Use code “DEANNACAT” to save 15% on the Plant Success website)

DeannaCat is holding a package of water soluble mycorrhizae from Plant Success Organics. Beyond lies a wheel barrow with an uprooted small kumquat tree inside as well as an arch beyond that with dense green passion fruit vines covering it. This leads to an area that is lush with lavender, vines, and rosemary bushes.
A two part image collage, the first image shows a recently uprooted small kumquat tree that is laying in a wheel barrow with soil below it. It fibrous roots are exposed with little to no dirt making up the root ball. The second image shows the kumquat after it has been transplanted into a 10 gallon plastic terra cotta color pot. A watering can is sticking into the frame from the edges of the image, watering the transplanted tree with water soluble mycorrhizae.
We recently dug up a kumquat tree that was not thriving in its current location in the garden. Unsure of where we want to plant it yet, we opted to re-home it into a large pot for now. To minimize the transplant shock and give the tree a boost, we thoroughly watered it with Plant Success water-soluble mycorrhizae after the move. Several weeks later, it looks great and hasn’t dropped a single leaf!

Can mycorrhizae be harmful to plants?  

There is virtually zero risk of harming plants by using mycorrhizal fungi products in your garden, especially if you follow the application directions provided. Even then, it is difficult to ‘overdo it’. Mycorrhizae is not a fertilizer and therefore cannot “burn” your plants like a high-nitrogen product might. If excess beneficial fungi are added to the soil beyond what can form associations with plant roots, they will simply die. 

Where does mycorrhizal fungi come from? 

The relationship with mycorrhizae and plants can be traced back millions of years. According to genetic studies, prehistoric ocean-dwelling plants began to slowly migrate onto land approximately 700 million years ago. They had very minimal root systems, and the soil was tough and unforgiving. Over time, plants partnered up with the fungi that already ruled the land. They evolved together to improve soil: plants developed more complex root systems, nutrient cycles became established, organic matter grew (and decomposed), and terrestrial life as we know it flourished. 

Modern mycorrhizal products are created at facilities that ‘farm’ or breed select strains of naturally-occurring beneficial mycorrhizal fungi. Mushrooms and fungi reproduce by releasing spores. Those spores are then collected, turned into mycorrhizal inoculant products, and sold with the spores in a dormant state. Later, once they’re added to your soil and come in contact with living plant roots and moisture, the spores will germinate and become one with the roots!

A cylindrical container of Plant Success Organics granular mycorrhizae sit in the foreground on the edge of a garden bed. Beyond lies two 6 cell packs of basil seedlings with two large tomato seedlings towering over them from behind. The backdrop is dense green with salvia, nasturtium, as well as a magnolia tree, a fig tree, and avocado tree.
Transplanting day for tomatoes, basil, flowers and more – with a side of mycorrhizal fungi.

Remember: feed the soil, not the plant!

Organic gardening is all about building and maintaining rich healthy soil as opposed to simply fertilizing plants, and it’s safe to say that mycorrhizae are an essential part of a complete soil ecosystem! I hope you enjoyed this mycorrhizae 101 lesson and learned something new. Are you excited to inoculate your garden with mycorrhizae too? Please feel free to ask questions in the comments below, and share this article if you found it valuable. Last but not least, we want to thank Plant Success Organics for sponsoring this post. And thanks to you all for tuning in!

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DeannaCat signature, keep on growing


    • Tajudeen Kazeem

      I live in Houston Texas where all we have is chlorinated water supply. I leant this is not good for mycorrhizal. How can I go around this

      • Aaron (Mr. DeannaCat)

        Hi Tajudeen, most city water has chlorine and while it isn’t optimal, there isn’t a lot you can do about it when it comes to watering your garden. There are filters you can attach to faucets or garden hoses that may filter some of the chorine. If you strive to have soil that is teaming with microbial life and quality compost, it will usually be enough to counteract the properties of chlorine, leaving you with quality soil and healthy plants. Hope that helps and good luck!

  • Paul Ritchie

    How effective is water soluble mycorrhizae at penetrating the soil and getting to the roots of already established plants/trees?

    • Aaron (Mr. DeannaCat)

      Hi Paul, as long as the soil around your plants or trees will readily absorb water, the mycorrhizae should have no problem penetrating the soil and coming into contact with the plant/tree roots. Hope that helps and have fun growing!

  • Alexandria

    This was such a fantastic read! Thank you so much for sharing. I’m growing a huge garden this year to replace having to go to a conventional grocery store to shop. I was wondering how much you used/recommend buying of the granular & water soluble products?

    • Aaron (Mr. DeannaCat)

      Hi Alexandria, it’s great to hear you are going to be expanding your garden this year, it will definitely help offset your grocery bill. We mostly use the granular mycorrhizae and I think the 16 oz. can should be more than enough for you. You only need to apply 1/4 teaspoon to seedlings that are in a 4 inch pot or less to even smaller ones. Hope that helps and have fun in your garden!

  • Dana

    This is the second article of yours that popped up in my searches this week. It was very helpful and I am headed out now to water my new transplants with mychorizzae with confidence! Thanks!

  • Beth

    Hi! This was our first season using mycorrhiza in our beds and today we pulled our tomato plant root out to see how the mycorrhiza worked on it. The roots alarming look quite a bit like they could have been affected by root knot nematodes, but some mycorrhiza pictures show similar nodes structures on the roots. Are you familiar if they look similar or should we worry we could have root knot nematode issues. The tomatoes produced great all year so it would be surprising but we aren’t sure. Thanks in advance!

    • Aaron (Mr. DeannaCat)

      Hi Beth, the use of mycorrhizae is said to reduce the damage done by root knot nematodes although it is still possible. You can treat your soil with beneficial nematodes, we have used this particular one and it works for a wide range of soil dwelling pests. Planting french marigolds along with your tomatoes is also said to reduce root knot nematode damage although it is best to leave their roots in the soil, just cut the plant out at the soil line once it has reached its end of life. Hope that helps and good luck, it’s great to hear you had a very productive season growing tomatoes as it was!

      • Sarah

        Just bought 5 pounds of the granular straight from the plant success organics website! Using your discount code and their extremely reasonable shipping rate, I’m very very pleased with my purchase price! Way way way cheaper compared to Amazon pricing!!! I’m super duper excited to try this for the first time this year on all my transplants. It’s going to be the best gardening year yet! Thank you so much!!!

        • Aaron (Mr. DeannaCat)

          That’s amazing to hear Sarah! Thank you for using our link and supporting Plant Success Organics directly, we have really enjoyed working with them and they are great people! We think you will love the mycorrhizae and it should last you many seasons of growing. Hope you have an awesome year in the garden and have fun growing!

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