The Benefits of Using Mycorrhizae in the Garden

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.

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! 

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!

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!

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

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)

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!

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!

Don’t miss these related articles:

• What is No-Till Gardening or Farming (aka No-Dig): Benefits Explained
• Composting 101: What, Why and How to Compost at Home
• How to Make Actively Aerated Compost Tea to Feed Your Garden
• Transplanting Seedlings Outside: Tips for Success
• How to Fertilize and Amend Soil Between Seasons