There is no questioning the importance a healthy root system plays in creating vibrant plants. After all, the root mass is the main channel for nutrient absorption, the foundation for structural integrity and the area where the largest population of beneficial microorganisms can be found.
The more we learn about the physiology of the plant’s roots, the more we realize how vital these beneficial microorganisms are—there would be virtually no plant life on the planet without their valuable symbiotic relationship with our plants.
Throughout the years, indoor horticulturalists have developed many products and techniques to promote and enhance the root growth in their gardens. Every one of these products or techniques is based on the same philosophy: attempting to mimic, enhance or supplement microorganisms found in the rhizosphere (the narrow region of soil affected by root secretions).
By using certain additives, a grower can maximize the size of their plant’s root mass and provide a larger surface area for moisture and nutrient absorption.
Additives that mimic
One of the many things plants gain from their symbiotic partnership with microorganisms is accelerated nutrient uptake. This is a result of by-product enzymes produced by the microorganisms.
Enzymes are catalysts that accelerate the rate at which chemical reactions occur. In this case, the chemical reaction is the uptake of nutrients by the plants roots. Your favorite enzyme formula designed for root enhancement is most likely a concentration of specific enzymes secreted by beneficial microorganisms.
Hydroponic horticulturalists gain the largest benefit from these enzyme formulations, especially if they use hydroponic systems that have no medium that would naturally harbor beneficial microbes. Growers who supplement enzyme formulas are essentially bypassing the microbes themselves and directly placing specific enzymes in the root zone.
Additives that enhance
Both parties must benefit for a relationship to be symbiotic. We know that beneficial microbes colonize on the root zone, thus preventing infections from pathogenic fungus, and produce enzymes that speed nutrient absorption. But how do the microorganisms benefit from the relationship?
The answer is sugars—more specifically, carbohydrates that are translocated from the plant (usually from the leaves) to the roots for the microbes to feed on. The microorganisms use the carbohydrates for energy, which allows them to function and reproduce. This is why carbohydrate supplements are so popular in the indoor gardening industry.
By directly supplementing carbohydrates to the root zone, a grower can accelerate the reproductive rate of beneficial microorganisms while allowing the plant to retain a good portion of the carbohydrates normally secreted through its roots. The carbohydrates that remain in the plant can be used for other purposes like creating terpenes and terpenoids, which are imperative for promoting flavor, smell and essential oils.
However, growers that supplement carbohydrates should always be on the look out for any sign of a pathogenic microorganism infection, as these microorganisms feed on carbohydrates as well. Supplementing carbohydrates to pathogens will accelerate their reproduction and can be devastating, so growers should immediately stop supplementing carbohydrates at the first sign of a potential pathogenic infection.
Supplying additional microorganisms
The most logical way to promote additional microorganisms into the growing medium is to directly supplement them. Almost every nutrient manufacturer has designed some sort of beneficial microorganism supplement, and the most common strains of beneficial microorganisms used can be broken down into three categories: trichoderma, mycorrhiza and beneficial bacteria.
All three types of supplements come as a liquid, a powder or in enclosed packets that resemble tea bags. Liquid microorganism supplements are usually designed, in both their composition and pH value, specifically for hydroponic systems. The powder form microorganism supplements have a longer shelf life than their liquid counterparts, and they are more compatible with soil or coco coir.
The packets are suitable for both hydroponic and soil applications, and have about the same shelf life as the powder formulas. No matter which form you decide to use, always make sure to check the expiration date. As with food expiration dates, this date is not an absolute (not every one of the strains of beneficial microorganisms will die on that date); however, the formula will be less effective if it is way past its prime.
Trichoderma is a genus of fungi found in all soils. Members feed on other fungi and cellulose by releasing chitinase enzymes, which break down chitin (the main component of fungal cell walls), and cellulase enzymes, which break down cellulose. Trichoderma’s symbiotic relationship with plants is directly related to those two enzymes.
In environments where there is an abundance of pathogenic microbes, which could cause disease in plants, trichoderma will produce more chitinase enzymes and rely on the pathogens as their main food source. This is why many growers add trichoderma to their medium as a precautionary measure against any pathogens in or around the plants’ roots.
The other enzyme, cellulase, can be beneficial in two ways. First, it makes certain nutrients available to the plant for uptake as it breaks down organic material in the soil. Secondly, trichoderma’s production of cellulase allows the fungus to penetrate the cells in a plant’s roots.
When the plant senses this, it turns on its natural defenses, which help boost the plant’s immune system. Since trichoderma cause the plant no real harm, both parties benefit—trichoderma gets sugars from the roots and the plant gets a heightened resistance to unwanted pests.
Mycorrhiza literally means fungus-root, and it is this fungus strain that is the true definition of a symbiotic relationship (over 90% of plant species in nature form a symbiotic relationship with these amazing creatures). These specialized fungi are essentially extensions of the root system, stretching far into the depths of the soil. In fact, mycorrhizal fungi can increase the absorbing surface area of a plant’s roots by 100 to 1000 times, which greatly improves access to soil resources.
As with trichoderma, it is the enzymes mycorrhizae produce that make them so invaluable to their plant partners. Mycorrhizae release enzymes that dissolve otherwise hard to capture nutrients, such as organic nitrogen, phosphorus and iron. The intricate web of mycorrhizal fungus captures and assimilates nutrients for the plant, and in return, the plants’ roots secrete sugars or carbon for the fungi to feed on. Mycorrhizae can be broken down further into subcategories; of these, two are commonly used in indoor horticulture: endomycorrhiza and ectomycorrhiza.
Endomycorrhizae are mycorrhizae whose hyphae (the branching filamentous structures of a fungus) penetrate the plant cells. The hyphae do not penetrate the interior of the cell, but essentially turn the cell membrane inside out. This increases the contact surface area between the hyphae and the cytoplasm, helping facilitate the transfer of nutrients between them.
Ectomycorrhizae are fungi that bear a hyphal sheath that surrounds the root tip. Ectomycorrhiza also have a Hartig net, which is basically an extended hypha that surrounds the outer layer of the root mass. It is the Hartig net that allows the transfer of nutrients, carbon and sugars, and completes the symbiotic relationship. An interesting fact about ectomycorrhiza is that plants sharing the same soil can actually transfer nutrients to one another through the ectomycorrhizal mycelium network.
Beneficial bacteria have made a strong impression in the indoor horticultural industry because they can be used as a foliar treatment, as well as a soil or medium additive. When added to the soil or medium, beneficial bacteria quickly colonize and feed off organic matter or pathogenic microorganisms. As they break down organic matter, they turn it into soluble compounds that are more easily absorbed by plants.
The consumption of the pathogenic microorganisms is beneficial because pathogens that are eaten can’t adversely affect the plant. Organic fungicide and pesticide manufacturers have jumped on the beneficial bacteria bandwagon as well, since certain bacteria (bacillus subtilis, for example) will consume pathogenic fungus on the surface of a plant’s leaves as well as in the soil. Many insects also refuse to feed or lay their eggs on plants that have been sprayed with beneficial bacteria formulas.
Just as every garden is different, every gardener’s methods and techniques will differ greatly. However, regardless of the technique or method used, it is crucial for every indoor horticulturist to stimulate the growth going on below the surface.
Current innovative horticultural products allow growers to mimic, enhance or supplement microorganisms, or—better yet—combine all three approaches to supercharge the complex microscopic ecosystem that is the foundation for plant health and vitality.