How Mycorrhizae Provide Value at Your Greenhouse or Nursery

Plant roots can only absorb a small volume of nutrients before they hit their depletion zone. One of the benefits of mycorrhizae is it can extend the depletion zone out into the growing media.

Plants have evolved over the years to develop several mechanisms that help them interact with microorganisms to acquire nutrients from the soil. One of the most widespread symbiotic relationships occurs between arbuscular mycorrhizal fungi (AMF) and most major agricultural crops and herbaceous and shrub species in natural ecosystems. This mutually beneficial relationship, known as arbuscular mycorrhizal symbiosis, facilitates nutrient uptake and exchange between the plant and the fungi. The plant sends carbon (e.g., sugar, lipids) to the fungus, and in return, the fungus provides the plant with inorganic nutrients and water.

Mycorrhizae Extend the Depletion Zone

After establishing itself in the root tissues of the plant, the AMF develops an external mass of branched, tubular filaments (hyphae) that act as a bridge that connects the root with the surrounding soil microhabitats. Mycorrhizae serve as extended arms to the plant root system by boosting its capacity to uptake nutrients and absorb water. On their own, plant roots can only absorb a small volume of nutrients before they hit their depletion zone, which in simplest terms is the zone around roots (or fungal hyphae) where the concentration of nutrients is lower than in the surrounding bulk soil. The depletion zone is particularly important for immobile nutrients such as phosphorus.

To obtain more phosphorus, plants must overcome the limitations of this depletion zone. Mycorrhizal hyphae serve this very purpose by reaching out of the depletion zone, and improving the ability of the plant to access additional soil resources.

It is well documented that mycorrhizal symbiosis increases the absorption area of the plant roots by up to 50 times. The mechanisms by which mycorrhizae increase absorption include some that are physical and some that are chemical. Physically, most mycorrhizal mycelia (hyphae) are much smaller in diameter than the tiniest root or root hair, and thus can explore areas of the soil that roots and root hairs cannot reach, and provide a larger surface area for absorption. Chemically, the cell membrane chemistry of fungi differs from that of plants. For example, they can secrete organic acid that dissolves or chelates many ions, or releases them from minerals by ion exchange, converting these nutrients into bioavailable forms. This becomes important in root-bound situations (e.g., in containerized plants), where roots are limited to a small volume of soil and there is no possibility for the mycorrhizal hyphae to explore larger soil volumes.

Cost-Effective Uses for Mycorrhizae

Mycorrhizae are relatively easy to use in various horticultural applications. The key is that the mycorrhizal propagules (reproductive structures) need to be in close proximity to actively growing root tips, as root exudates (discharges of fluid) trigger the germination of the dormant propagules, and kick off the symbiotic colonization of the root system. These mycorrhizal inoculant products can be used as a seed treatment, applied to unrooted cuttings, incorporated into growing media, or even used as a drench or plug-tray dip.

Early colonization by the mycorrhizae is the most cost-effective, as young plants require less inoculum, and provides a faster response, especially for short-term crops grown in greenhouses. However, it is never too late to top-dress or incorporate the mycorrhizae into a container substrate or the landscape soil. The key is to mix the mycorrhizae thoroughly into the soil or to apply enough water to move them into the future root zone of the plant. For the landscape, spring and fall applications are preferable because the roots are more active than during the winter or summer.

Influence on Phosphorus Uptake

One of mycorrhizae’s benefits is its ability to provide significant amounts of nitrogen and phosphorus to the plant in exchange for carbohydrates. If the plant receives extensive amounts of fertilizer, it will not signal the mycorrhizae to germinate and form the symbiotic colonization of the root system. High nitrogen levels increase vegetative growth at the expense of root growth, so reducing nitrogen levels in your fertility program benefits both the mycorrhizae and the plant. High levels of soluble phosphorus can inhibit colonization and mycelial growth, so it is recommended to use fertilizers with a low phosphorus concentration. For example, a fertilization program of 200 ppm nitrogen (N) using a 20-20-20 fertilizer could be reduced to 100 ppm N using a 20-2-20 fertilizer, which would reduce nitrogen by 50% and phosphorus by nearly 95%. Growers should consider these potential savings and plant enhancements based on their growing conditions. The use of controlled-release fertilizers is also a consideration for a lower fertility regime.

Rethink Common Production Practices to Preserve Soil Health

Mycorrhizae can be harmed by some horticultural practices. Steaming the soil after application of mycorrhizae is detrimental. A few fungicides can also harm germinating mycorrhizae propagules. An updated listing of the effects of fungicides on mycorrhizae is available at If there are doubts, it is best to treat with fungicides two to four weeks after application of the mycorrhizae.

Although some benefits of mycorrhizae on a crop may occur after inoculation, it often requires four to eight weeks before there are visibly noticeable plant responses. When applied early in the crop cycle or at transplanting, benefits continue to develop as more roots develop, whether in a container or in the landscape. Mycorrhizae have an important role in horticulture, especially under stressful conditions, and they are not harmful to plants, people, or the environment.

Six Considerations for Choosing the Right Mycorrhizae Product

There are several mycorrhizal products on the market for professional growers. It is very important to make the right decision for product choice for best efficacy. When evaluating the available options, here are some important points to consider:

  • Know your need. Mycorrhizal fungi can be used to increase water and nutrient uptake by enhancing root growth, maintaining optimal plant growth under stressful conditions, increasing general plant health, and reducing transplant shock.
  • Established product performance. Make sure the product has been on the market for some time and its performance has been published in technical magazines/journals (i.e., tested by growers and independent researchers).
  • Product quality. The product must contain viable and infective mycorrhizal inoculum at a rate that is listed on the label.
  • Producer credibility. The producers/manufacturers have delivered what they promise on their label.
  • Technical service. The technical staff of the producer/manufacturer can be reached with various technical questions and regarding product use. Larger, more reputable companies offer services such as testing the mycorrhizal colonization of roots after application to check product efficacy.
  • Diversity of mycorrhizal fungal species. This is critical to achieve maximum efficacy. There are several species of mycorrhizal fungi in the soil. The mycorrhizal fungal community changes over time with plant phenology, season, microclimate, and soil conditions. Furthermore, different species are responsible for different functional benefits to the plant. Therefore, products containing multiple mycorrhizal species appear to provide more consistent benefits to the plant and ultimately to the grower.
Topics: , ,

Leave a Reply

More From Media...
Dallas Johnson Greenhouses

April 14, 2018

Kemin Forms Distribution Partnership With Plant Products

Under the agreement, Plant Products will be a Kemin Crop Technologies’ distributor in the northeastern U.S.

Read More

April 13, 2018

Dümmen Orange Debuts New Rooting Technology

Basewell bare-root cuttings feature advanced root development and no growing media, which allows products to ship to growers from off-shore production locations, ready to transplant directly into the finish container.

Read More

April 10, 2018

New Tool Helps Greenhouse Growers Analyze Irrigation Water Quality

The University of Connecticut and University of Florida have partnered to launch the WaterQual tool as part of the CleanWateR3 research program.

Read More
Latest Stories

February 18, 2018

Why Biochar Might Eventually Replace Peat Moss

In a recent study, researchers from the University of California, Davis investigated biochar as an alternative to peat moss.

Read More
Soil-pH feature

January 7, 2018

How Direct-Stick Meters Can Help Take the Guesswork Out…

Monitoring your soil pH is critical to maintaining the health of your greenhouse crops. Try these tips for managing pH, as well as accurately testing your soil with direct-stick soil pH meters.

Read More
Peat vacuum harvester

December 8, 2017

The Sustainability of the Peat Industry Looks Better T…

Despite talk about alternative products and differences of opinion over its sustainability as a resource, peat is here to stay.

Read More

December 6, 2017

How Mycorrhizae Provide Value at Your Greenhouse or Nur…

Mycorrhizae create a connection between the roots of a plant and the surrounding growing media. This ultimately leads to better crop health through enhanced nutrient and water uptake.

Read More

November 13, 2017

Michigan State Offering Online Root Zone Management Cou…

Participants in the three-month, self-paced online course can learn about water quality, plant nutrition, and irrigation management.

Read More

November 13, 2017

International Growing Media Symposium Comes to the U.S.

This International Symposium, with representatives from 21 countries, covered new market opportunities, generated innovative ideas, and offered first-hand information to more than 150 attendees.

Read More
Oasis PlantPaper

September 25, 2017

Oasis Introduces New Biodegradable Paper Wrap for Plant…

PlantPaper is an all-natural, bio-based, wrap media that contains no glue and provides more effective rooting.

Read More
LM-Bark 1 (Lambert Peat Moss)

September 25, 2017

European Growing Media Manufacturers Face Challenging M…

Rising costs and a poor harvest have created challenging conditions for the growing media industry in 2017, according to the UK-based Growing Media Association.

Read More
Growing Media Mixing Model

August 28, 2017

New Mixing Model Predicts Rooting Media Properties

Researchers at Wageningen University & Research have developed a mixing model that predicts the properties of a mix of constituents in any growing media ratio.

Read More
Vijay Rapaka

July 30, 2017

Oasis Grower Solutions Hosting Plant Production Webinar

The webinar, which takes place on Aug. 10, will provide information on growing media for cutting propagation and seed germination.

Read More
New Growing Media Blends

July 26, 2017

British Researchers Evaluating New Media Blends to Redu…

Research in the United Kingdom has shown that coir-free growing media has the potential to work as well as coir for strawberry crops, and these research results likely apply to greenhouse production, as well.

Read More
Iron and Manganese toxicity in geranium

June 13, 2017

Are Your Geraniums Showing Signs of Iron or Manganese T…

Zonal geraniums with low pH can exhibit iron and manganese toxicity symptoms, including marginal chlorosis, leaf speckling, and upward-cupping of the leaves, according to Michigan State University experts.

Read More
GrowTech CatEyePlug Feature

June 6, 2017

Grow-Tech Introduces New Media Plug, Joins Dümmen Orang…

Grow-Tech LLC, a designer and manufacturer of stabilized growing media products, is making waves this week with the launch of a new plug and an announcement that it is joining forces with Dümmen Orange.

Read More

May 9, 2017

How to Test and Correct for Low Substrate pH in Your Gr…

If you mix your own or purchase a pre-mixed substrate, it is recommended you determine the initial pH. In too many cases, growers end up discovering low substrate pH.

Read More

January 2, 2017

Why You Need To Know What’s In Your Growing Media…

Before you buy growing media mixes or raw materials to mix your own custom blends, here are some important factors to consider.

Read More

December 25, 2016

Grow-Tech Patents Plug Designed for Tissue Culture

The ZenPlug from Grow-Tech is used for tissue culture in orchids and difficult-to-root cuttings, and is one of several products recently developed by Grow-Tech.

Read More
Various Wood Substrates

December 18, 2016

The Evolution And Revolution Of Wood Substrates

Growing media formulations are evolving as researchers fine tune blending techniques for wood component substrate alternatives to achieve reliable, consistent results.

Read More

December 17, 2016

New Growing Media Technology Designed To Promote Health…

Oasis Grower Solutions recently launched several new innovations that support plant growth and health all the way to maturity.

Read More