Mycorrhizae use in nursery and greenhouse production can enhance nutrient absorption and plant growth

Mycorrhizal fungi are beneficial microscopic soil organisms that have evolved in a symbiotic relationship with approximately 95% of the world’s plant species over the past several hundred million years. These fungi predate the evolution of terrestrial plants, and it was the partnership with mycorrhizal fungi that allowed plants to begin to survive on dry land and ultimately lead to life on Earth as we know it.

Although these beneficial soil organisms have been a bit of a buzzword in the horticulture world over the past few years, mycorrhizae are not new; in fact, they have been around for hundreds of millions of years, quietly doing their important work beneath our feet.

The relationship between plants and mycorrhizal fungi is a two-way relationship of sharing resources between species, thus a classic symbiotic mutualism. The endomycorrhizal fungi rely on the plant to survive, and the plant’s performance and survival are enhanced by these beneficial fungi.

Mycorrhizae act as a living extension of the plant’s roots and benefit a plant’s root system development, nutrient and water uptake and efficiency, stress tolerance, and transplant success. For a professional grower, mycorrhizal fungi can shorten crop times, improve plant uniformity, reduce nutrient runoff, allow for longer watering intervals, add to transport and retail resiliency, and improve soil quality and health.

The per-plant investment can be as little as $0.0002 – $0.0008 when treated early in the plant’s life cycle. Inoculating horticulture crops with mycorrhizal products provides an inexpensive insurance policy. Once the plant root system is colonized by the mycorrhizal fungi, this symbiotic relationship lasts the lifetime of the plant as the mycorrhizal hyphae continue to grow along with the roots.

With recent advancements in formulations and carrier technologies, professional horticulturists can easily incorporate mycorrhizae into their growing protocols.

Selecting the right type of mycorrhizal product

With all of the mycorrhizal inoculum options currently on the market, selecting the best mycorrhizal product for growing operations is very important, as not all products will work for all plants and crop types, and not all products are created equal.

First, there are two different major types of mycorrhizal fungi that are commercially available: endomycorrhizae and ectomycorrhizae. A brief overview of the mycorrhizal fungi types are in chart 1 (below).

In general, most greenhouse ornamental crops (and vegetable crops) will require endomycorrhizae only, however, some nursery growers can benefit from both endomycorrhizae and ectomycorrhizae, if they are growing a combination of flowering ornamental plants as well as woody shrubs, nut trees, or conifers. Christmas tree producers or forestry nurseries will require only ectomycorrhiae for their crops.

Some products on the market contain endomycorrhizae only, some contain both endo and ecto, and some contain ectomycorrhizae only. Selecting a product that contains only the mycorrhizal type(s) that an operation need will help ensure the success of the inoculant and help to ensure a return on investment.

Another major consideration when selecting the optimal mycorrhizal product is the diversity of mycorrhizal species that are included. The growing media or soil within the root zone is an ecosystem, and just as it is with any ecosystem, species diversity is important. Some products on the market include only one mycorrhizal species, while others contain as many as nineteen mycorrhizal species.

These different mycorrhizal species provide distinct benefits to the plants under varying circumstances, different forms of plant stress, and through different stages in the growing season and plant life cycle. As a general rule, greater species diversity will provide a wider and more complete range of benefits from the mycorrhizal symbiosis.

Horticulture application options

With the various mycorrhizal inoculant formulations now available in the horticulture market, there are a large variety of options for professional growers to effectively inoculate ornamental crops with these beneficial symbiotic soil organisms. In the past, mycorrhizal inoculation often required an additional step in the production protocol, which could be time consuming and labor intensive. These days, many products on the market are designed to eliminate extra steps and make the process as smooth and efficient as possible, at any stage in the production process.

The key to applying mycorrhizal products is to make physical contact between the product and the growing or emerging roots. The closer the active ingredient is placed to the roots or seed, the faster and more effectively the symbiosis will be established. In order to accomplish this, growers have several options: soil/media incorporation, tray dip, bare root spray or dip, or soil/media drench (via spray, sprinkler irrigation, drip irrigation, watering can, or any way to get a thorough drench of the root system and move the active ingredients in to the root zone).

The most cost-effective and efficient stage in the plant production process to apply a mycorrhizal inoculant is during propagation, or as early as possible in the production process. This way, growers are treating the minimum soil volume, which will require less inoculant product per plant. And as the plant grows and is transplanted for finishing and then ultimately outplanted in a landscape, installation, basket, etc., the mycorrhizae will continue to grow in the larger soil volume along with the plant’s roots, and ultimately out into the nutrient depletion zone that roots alone cannot access.

For medium or large-scale growers, the most efficient application method is generally to drench plugs or propagation trays using a highly concentrated suspendable product that is suitable for application through a horticulture injector system. This way, the product can be applied via irrigation, boom spray, drip, etc., and can often be included along with the application of another input such as liquid fertilizer, which completely avoids the need for any additional steps or input applications in the production protocol.

Alternatively, for growers who mix their own propagation media, there are granular products on the market that are ideal for mixing with soil or media, which can also be a very cost-effective and efficient way to give plants a boost.

Contact a distributor

Mycorrhizal fungi are the most well-researched soil organisms on the planet, and the benefits that they provide to plant vigor, growth, and productivity are extremely well documented.

Professional mycorrhizal inoculant products are available from most major greenhouse and nursery distributors throughout Oregon and the rest of the U.S. For more information, and most horticulture distributor sales representatives and websites will be able to point you towards the options that they offer.

Graham Hetland is the product and communications manager at Mycorrhizal Applications, based in Grants Pass, Oregon. He holds a bachelor’s degree in environmental studies as well as an MBA from Southern Oregon University.  He can be reached at [email protected] or 541-476-3985.