There is a vast, complex system of microbial life in and around a plant’s root zone at all times. This congregation of beneficial microorganisms works synergistically with plants. In most cases, the microorganism receives nutrition and, in return, aids in the breakdown of organic matter. Many microorganisms create enzymes as byproducts which act as catalysts for the multiple chemical reactions happening in and around a plant’s rhizosphere. Even though many of these microorganisms exist naturally in healthy soils, commercial horticulturists have been enhancing growth and increasing yields by supplementing additional microorganisms to their crops. In more recent years, hobby growers have started to gain the benefits of supplementing beneficial microorganisms. The types of beneficial microorganisms most commonly used in microorganism supplements can be broken down into three categories: mycorrhizae, trichoderma, and beneficial bacteria.
Mycorrhizae are naturally occurring fungi that form symbiotic relationships with over 90 percent of the world’s plant species. These microorganisms are becoming more readily available to the hobbyist grower. Mycorrhizae have become a common additive in gardening products such as potting soils and organic lawn fertilizers. Many garden retailers will carry mycorrhizae in a powder form which can be added as desired by the gardener. Mycorrhizae formulas are also available in liquid form although the powdered form is more stable which makes it easier to store. The reason mycorrhizae supplementation has become so popular is because it is an extremely effective, yet affordable, organic growth enhancer. Mycorrhizae fungi become an extension of the root system which stretches far into the depths of the soil. This immediately broadens the plant’s access to vital nutrients. Mycorrhizae have synergistic relationships with the plant’s roots. The extending web of mycorrhizal fungi assimilates nutrients for the plant and, in return, the plant’s roots secrete sugars or carbon for the fungi to feed on. It is actually the enzymes produced by mycorrhizae fungi that make them such assets to their plant partner. The enzymes released by mycorrhizae dissolve otherwise hard to capture nutrients such as organic nitrogen, phosphorus and iron. Although many mycorrhizae formulations contain both types of mycorrhizae and are sold as a general mycorrhizae supplement, there are actually two types of mycorrhizae fungi used by horticulturists for their beneficial properties: endomycorrhiza and ecomycorrhiza.
Endomycorrhizas are the type of mycorrhizae whose hyphae (the equivalent of vegetative growth of a fungus) penetrate the plant cells. Instead of penetrating the interior of the cell, the hyphae manipulates the cell membrane (turning it inside out) which increases the contact surface area between the hyphae and the cytoplasm. This helps to facilitate the transfer of nutrients between them; requiring less energy than would otherwise be needed by the plant to do so.
Ecomycorrhizas are a group of fungi that have a structure which surrounds the root tip. Ecomycorrhizas basically surround the outer layer of the root mass. In nature, vast networks of ecomycorrhizas extend between plants (even plants of different varieties) and allow plants to actually transfer nutrients to one another.
Although most formulations contain both types of mycorrhizae, endomycorrhizas and ecomycorrhizas can be sold individually. The product’s label will always disclose the percentage of each type of mycorrhizae it contains. The label should also have an expiration date. Close attention should be paid to the expiration date of any microorganism supplement. Although powdered form supplements generally have a long shelf life, microorganisms are living creatures and their effectiveness dwindles as they age and die out.
Trichoderma are a group of fungi that are usually implemented by horticulturists as a defense against pathogenic fungi. This is because trichoderma are specialized fungi that feed on other fungi. As with mycorrhizae, the benefits derived from trichoderma are directly linked to the specific enzymes they release. Chitinase enzymes released by trichoderma break down chitin. Chitin is the main component of fungal cell walls. The other important enzymes produced by trichoderma are cellulase enzymes, which break down cellulose.
It is the chitinase enzymes produced by trichoderma that are responsible for trichoderma’s reputation of warding off pathogens. When many pathogenic fungi exist in the soil, trichoderma will increase its chitinase production and feed almost exclusively on the pathogen. This eliminates pathogens that could seriously hinder or damage the plants. In fact, many hobbyist gardeners are starting to add trichoderma to the soil as a precautionary measure.
Cellulases, which are also enzymes produced by trichoderma, are beneficial in two ways. First, cellulases break down organic material in the soil which makes particular nutrients more readily available for plant absorption. Second, the cellulases produced by trichoderma penetrate the cells in the plant’s roots. This instantly triggers a plant’s natural defense, much like a human’s immune system. The plant’s metabolism is stimulated and no real harm is caused to the plant. Trichoderma are another example of synergy between plants and microorganisms. The trichoderma feed on sugars secreted by the plant’s roots and the plant gets a heightened resistance to pests and pathogens.
Beneficial bacteria have made great strides in the horticultural community. As with beneficial fungi, bacteria can be added to the soil or medium to break down organic matter, facilitate nutrient uptake and add protection against pathogens. One huge advantage of using beneficial bacteria in horticulture is that, under the right conditions, bacteria have the ability to quickly colonize and explode in population. This means they are able to quickly feed on or destroy pathogenic microorganisms and break down organic matter. As bacteria colonize and break down organic matter, they convert it into soluble compounds that are more readily available to plants.
Aside from adding beneficial bacteria to the plant’s root zone, there are many other applications for beneficial bacteria in horticulture. Many of the key ingredients in today’s organic pesticides and fungicides are beneficial bacteria. It has been discovered that certain bacteria, bacillus subtilis for example, will consume pathogenic fungi on the surface of a plant’s leaves as well as in the soil. This means beneficial bacteria are not only beneficial as a root drench but also as a foliar treatment. This is especially true for specific fungicidal and insecticidal applications. Particular strains of beneficial bacteria are being used as insecticides for a wide variety of insects. Some of these bacteria affect the way insects digest food and molt; while others inhibit the insect’s ability or desire to lay eggs. Generally speaking, insecticides derived from beneficial bacteria are safer to use than many of the chemical insecticides. Many leave no residuals and can be safely used to treat plants closer to harvest time. The uses of beneficial bacteria in horticulture will continue to expand as our knowledge about the various strains of bacteria continues to progress.
As gardeners, small growers and greenhouse hobbyists, we are continuously seeking new methods to improve the vitality of our plants. In more recent years, horticulturists, in general, have become more aware of the benefits that natural and organic solutions provide in both plant nutrition and also the defense against pests and pathogens. Beneficial microorganisms are literally the link between the plants we grow and the soil or medium they are grown in. Commercial growers have been reaping the rewards of increased microorganism supplementation for years. Hobbyist greenhouse growers can now find affordable beneficial microorganisms to experiment with in their greenhouses. From stimulating growth to increasing a plant’s natural defenses for battling pests and pathogens, microorganisms provide multiple benefits to all types of gardeners. They also offer a safer solution to many problems that would otherwise require toxic treatment programs to eradicate. There is no doubt that beneficial microorganisms will continue to shape the future of horticulture. Enhancing the connection between plants and beneficial microorganisms can only benefit the horticulturist. With the increasing availability of these beneficial microorganisms, there is no reason why greenhouse hobbyists shouldn’t benefit from one of nature’s most powerful synergistic relationships.
Eric Hopper is the MyGardenAndGreenhouse.com editor.