We had the awesome opportunity to sit down with Scotty Real of Real Growers and The Dude Grows Show. Scotty brought his 25 years of expertise to the table, helping us shed light on the dark corners of the soil world.
Before we jump into beneficial bacteria, we should first talk a little bit about the rhizosphere. Why? Because that is where you will find all of the bacterial action we are about to discuss. The rhizosphere is the microbial party zone.
Often called “the last frontier in agricultural science,” the rhizosphere is the area around a plant’s roots. What makes the rhizosphere more special than other areas in the soil? Roots release special compounds called exudates with which microbes interact, basically functioning as all-you-can-eat salad bars for our microbial friends. Root exudation is a complex process and the many compounds released by roots are not fully studied or understood. We do know, however, that some of these exudates are “amino acids, organic acids, sugars, phenolics” as well as polysaccharides.
Plant growth-promoting bacteria, or PGPB, are found within the rhizosphere of many plants and plant species.
All of these exudates create the ideal environment in which soil microorganisms thrive, and represent one of nature’s most important symbiotic relationships. For this reason, significantly more microorganisms are found directly around plant roots than in other areas of soil. We are talking about the first two millimeters around plant roots.
The amount of interaction between bacteria and plants plays a role in determining soil fertility and overall plant health. Although there are many types of microorganisms on earth, for plant health you want to look for a good mix of mycorrhizae, bacteria, and Trichoderma. If you want to learn more about mycorrhizae, check out our earlier post. For now, there are some special characteristics of bacteria that we want to focus on.
1. They Work With Synthetic Nutrients
“Microbes are not ONLY for organics.” – Scotty Real, Realgrowers & The Dude Grows Show.
Many growers have long believed that if they don’t grow organic, soil inoculation is a waste of their money. Scotty Real confirms this is not the case.
Bacteria strains are more durable than mycorrhizae when it comes to synthetic nutrients. Synthetic nutrients kill off mycorrhizae, so myco-only products are best used strictly in organic gardening. Bacteria, on the other hand, can withstand the concentrated nutrient levels found in synthetics.
If you are using synthetic nutrients, it is best to feed your plants first. Inoculate them with beneficial bacteria after feeding. Although beneficial bacteria work with synthetics, they don’t necessarily love each other. If you wait to inoculate after feeding, you reduce the risk of synthetic nutrients causing any harm to your inoculants, especially if you use a mix that also contains mycorrhizae.
Although they work with synthetics nutrients, bacterial strains can be equally beneficial to the organic gardener, as well as the conventional grower.
“In organic growing, you are trying to create this ecosystem that grows itself. So those mycorrhizae have to stay alive and those Trichoderma and bacteria have to stay alive so they can colonize and expand.”
2. They Increase the Bioavailability of Nutrients
“It is like a slow-release capsule of nutrition.”
Beneficial bacteria break down nutrients and minerals into smaller parts that plant roots can absorb more easily. These bacteria are an important part of the carbon and nitrogen cycles and increase nitrogen fixation in the soil.
According to the Annals of Microbiology, beneficial bacteria can also synthesize certain compounds, like hormones, that are good for plants.
They can have either a direct beneficial impact or an indirect beneficial impact on plants, depending on the type of bacteria present and its mechanism.
The production of plant hormones has a direct impact on plant growth. These hormones include auxins, cytokinins, gibberellins, ethylene, and abscisic acid. The root tip is the biggest site of cytokinin synthesis. Both cytokinins and auxins promote shoot development. Gibberellins promote overall plant growth, including germination and flowering. Ethylene, on the other hand, stimulates later parts of the life cycle, including flowering, fruit ripening, and leaf shedding. Lastly, abscisic acid helps plants respond to stress and promotes wintering behaviors. For instance, abscisic acid helps trees shed leaves, close stomata, and promote seed dormancy.
Beneficial bacteria “enhance resistance to stress, stabilize soil aggregates, break down organic matter and improve soil structure. PGPR retain more soil organic N, and other nutrients in the plant-soil system, thus reducing the need for fertilizer N and P and enhancing the release of the nutrients.”
Nitrogen goes through various transformations as it becomes plant food. Bacteria help with these processes. Nitrogen gas (N2) is absorbed into the soil but is unusable by plants in this form. Bacteria then convert the Nitrogen gas into Ammonium ions (NH4+), which can easily be utilized by plants. The only other naturally occurring usable form of Nitrogen is NO3-, which is converted by lightning in the atmosphere. It then enters the soil through rainfall. Without the conversion of N2 to NH4+ by beneficial bacteria, the plant would be waiting around for lightning to strike to receive nitrogen.
Nitrification is the conversion of ammonium to nitrate, which plants can use as food.
Plants can also use ammonium as food, so the biological breakdown of nitrogen into ammonium (called Assimilation or Mineralization) helps to feed plants, as well. This also feeds beneficial bacteria in the soil.
Nitrogen Fixation is the conversion of nitrogen gasses in the air to organic nitrogen for plants. Only certain bacteria and lightning can do this.
Bacteria also have an indirect impact on plant growth by inhibiting pathogens. Soil bacteria produce hydrogen cyanide. This is a compound that degrades the cell walls of the fungus. This weakens the defenses of the bad guys.
Many types of bacteria also produce compounds that give soil antibiotic properties. Certain bacteria create their own biofilm, which acts as a protective layer. When bacterial colonies are covered in biofilm, it is much harder for pathogens to break into those areas of the soil. In this way, established beneficial bacteria “elbow out” the pathogens by taking over all of the space around roots.
What does all of this mean for you? In soil, you are unlocking the full potential of the nutrients already present. You may also be able to reduce the number of pesticides needed in your grow. These same benefits may be available in hydro, as well.
3. Each Type of Bacteria Has a Specific Job
“You gotta get lazier. Let nature do more of the work.”
Naturally Occurring Bacteria
Bacteria comprise four main functional groups.
Many bacteria are decomposers. According to the USDA, they “consume simple carbon compounds, such as root exudates and fresh plant litter. Through this process, bacteria convert energy in soil organic matter into forms useful to the rest of the organisms in the soil food web. Several decomposers can break down pesticides and pollutants in soil. Decomposers are especially important in immobilizing or retaining, nutrients in their cells, thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.” In the words of Scotty Real, ” their cells are organics and naturally sticky so [nutrients] stay in the soil instead of washing away like salt on your skin after the beach.” These decomposers include Actinomycetes, which give soil its signature “earthy” smell. Bacillus strains are also considered decomposers.
Mutualists are nitrogen-fixing bacteria that form symbiotic relationships with plants. Rhizobium strains are mutualistic bacteria found in the root nodules of legumes. Mutualists also include Azospirillum, a bacteria that is closely associated with grasses.
Pathogens are dangerous for plants. These include Erwinia and Agrobacterium.
Erwinia causes fire blight on apples and pears. Agrobacterium causes Crown Gall disease in over 140 species of flowers. Just like with humans, pathogens make a plant sick.
Lastly, you have lithotrophs or chemoautotrophs, which get their “energy from compounds of nitrogen, sulfur, iron or hydrogen instead of from carbon compounds. Some of these species are important to nitrogen cycling and degradation of pollutants.” For instance, Nitrosomonas oxidize ammonia into nitrite and then Nitrobacter turns nitrite into nitrate through the same process. Chemoautotrophs include some Pseudomonas, as well.
There are tons of native bacterial strains found in soils, but only a few are available commercially. Certain strains of Bacillus, Pseudomonas, and Streptomyces can be purchased or found in inoculating products.
A good microbial inoculant will contain multiple beneficial strains of bacteria, as well as mycorrhizae and Trichoderma. One of our favorite microbial products, Recharge, contains four different types of beneficial bacteria (along with some mycorrhizae and Trichoderma). Recharge contains the following four types of bacteria for very specific reasons.
First of all, these four strains are symbiotic, meaning that they live harmoniously together. Not very many bacteria can do that, even beneficial ones. Most decomposers will try to digest other bacteria, even if they are beneficial.
Bacillus Licheninformis has antifungal properties because it produces an antibiotic that can help prevent plant diseases. It also produces enzymes that promote and facilitate the nutrient cycle.
Bacillus Pumilus promotes plant growth “by enhancing the uptake of nutrients, nitrogen fixation, interaction with symbiotic microorganisms and producing antimicrobial agents against pathogenic bacteria and fungi as well as by reducing metal toxicity”. Bacillus Pumilus is a type of Bacillus Subtilis, so can often share the same traits.
Bacillus Subtilus functions as an immune booster for soil and plants. It produces the antibiotics polymyxin, difficidin, subtilin, and mycobacillin. These antibiotics increase the “chance at survival as the organism produces spores and a toxin that might kill surrounding microbes that compete for the same nutrients.” They act as biofungicides and antibiotics for plants. B. Subtilus also creates a biofilm over its colonies. This biofilm protects plants from pathogenic infections, as well as preemptively colonizing areas. Preemptive colonization prevents pathogenic microbes from invading since the area is already claimed by beneficial microbes.
Bacillus Megaterium is the most prevalent bacteria found in soil, hence the name “mega”. Bacillus Megaterium metabolizes soil components to create food for plants and other organisms. It does this by producing the enzyme amylase. Amylase is an enzyme that digests starches into sugars. Those sugars are then used as bacteria and plant food. Like all other beneficial bacteria, Megaterium contributes to the carbon and nitrogen cycles in soil, as well.
4. It Is Good for Any Type of Grow
Whether you are a tried and true soil gardener or committed to growing hydro, beneficial bacteria is a must-have in your grow.
The easiest, most cost-effective, and fastest way to inoculate your plants is with a pre-made product.
You can always brew your own compost tea, but there are products out there that have done the work for you. No matter the type of garden, you can easily inoculate your plants. The easiest and safest way, regardless of your growing method, is simply by top dressing. In either setup, pour directly onto your growing medium.
Avoid putting any type of product (especially ones that contain Molasses) into a hydro reservoir or irrigation system. That is a sticky mess waiting to happen!
5. You Can (and Should) Supplement Regularly.
By dumping synthetic macronutrients down your plant’s throats, you may end up with a fat plant, but you are just making plant foie gras instead of growing plant athletes.
If you want to build really strong, resilient, super healthy plants, it is important to be sure they are getting micro, as well as macronutrients. One of the best, most bio-available ways of doing that is to inoculate with beneficial microbes.
Since microbes increase the bioavailability of all nutrients, too much of a good thing can be a bad thing. You can cause a nutrient burn if you give your plants too many beneficial microbes.
The general rule of thumb is to inoculate once a week, whether growing in soil or hydro. This gives your plants enough time between doses so that you don’t cause nutrient burn, but frequently enough that they get all of the benefits.
The More You Know the Better You Grow
With a little help from our friends at Real Growers and The Dude Grows Show, we were able to dig in and break down beneficial bacteria. Here is the takeaway:
- It is perfectly safe, and advisable to add beneficial bacteria to your grow whether you are fully organic or conventional. They can take the heat of synthetic nutrients better than most microbes.
- Beneficial Bacteria are so important because it makes Nitrogen and micronutrients more bioavailable for your plants. If growing in soil, you get more for your money by unlocking the potential of your soil. If you are growing in hydro, you may be able to decrease the quantity of nutrients you use on your plants. Win!
- Not all bacteria are the same. Some bacteria are pathogenic. Stay as far away from those as you can. Bacteria also digest carbon and decompose organic matter into usable plant food. They can form symbiotic relationships with plants (mutualists). And chemoautotrophs are special because they turn nitrogen already present in soil into usable ammonium for plant food.
- You can inoculate your plants whether you are growing in soil, in hydro, indoor, outdoor, hand watering, or with an irrigation system. Simply mix up an awesome product like Recharge and top dress your plants! (After feeding if you are using synthetics)
- For best results, add beneficial bacteria once a week.