Many first-time cannabis growers don’t think too hard about the soil their plants will be growing in. If the soil looks healthy enough, it should be good to go, right? Well, it might be, but that isn’t enough information to tell for sure. If you really want to know whether your cannabis will thrive, you’ll have to see whether or not your soil contains a solid amount of microbes.
Microbes have a mutually beneficial relationship with the plants in their soil, and supporting microbes is one of the best ways you can support your cannabis. As we go along, we’ll be discussing the details of microbial presence in soil, the relationship between microbes and plants, and the specific organisms that make optimal growth possible.
Why Microbes Play a Vital Role in your Cannabis Plant Health
Microbes are key if you want your cannabis plants to grow as well as they can. If the idea of beneficial bacteria is strange to you, remember that we, ideally, have loads of bacteria in our bodies that keep us healthy. We’re not made of soil, of course, so things don’t work exactly the same, but the microbes in soil and those in our guts share key functions in common. Namely, as we’re about to explore, microbes provide vital nutrients to the plants in their soil, along with protecting them from harmful forces.
How Microbes and Cannabis Plants Work Together
With that in mind, let’s take a look at how the relationship between microbes and the cannabis plants you are growing play out in the soil. Plants need sufficient amounts of phosphorus, potassium, and nitrogen to survive and microbes have a direct hand in how much of those nutrients your plants receive.
While the nutrients may be in the soil already, they aren’t as accessible as they could be. Potassium, for example, is often shrouded in inorganic material. As microbes happen upon it, they’ll consume it, metabolize it, and excrete it in a form much more readily consumed by the plants. While the others aren’t as hard for the plant to get to, the microbes break them down nonetheless, and the plants benefit greatly from the enhanced access. This effort is further assisted by their ability to aerate the soil, ensuring there’s an even flow of water and nutrients.
The microbes aren’t only doing all this from the goodness of their heart, though. As the plants are fed, their roots excrete a collection of substances, called exudates, into the soil. These exudates, which include a variety of amino acids, organic acids, and sugars, happen to be a great source of nutrition for the microbes. With their microbe bellies full, the nutritional cycle is fully formed, and the plants are ready to thrive.
The Importance of Fungi for Growing Cannabis
While we think of fungi as separate from microbes, they’re part of the club too, and serve the same cause. To be clear, though, this is because they also partake in the exudates to stay fed.
Mycorrhiza fungi, in particular, can be found acting as the extension of plant roots, collecting nutrition from further down the soil than plants would be able to otherwise.
One type, ectomycorrhizae, acts as a sort of sheath for the root, extending out for nutrition. Endomycorrhizae, however, actually live inside the plant, helping to bring the nutrients straight into the root. To preserve them, ensure that you’re not being heavy-handed with fertilizers. Of course, you should also avoid fungicides entirely.
Microbial Dangers, and How Other Microbes Stop Them
As the fungi provide nutrients to the roots, they serve as a protective layer for them as well. But what, exactly, do they need protecting from? Well, among the beneficial microbes, there are thousands of microscopic worms, called parasitic nematodes, that feed on the roots of plants.
Looking from the outside, you’d notice roots facing attacks from ectoparasitic nematodes, which live in the soil right outside said roots (the rhizosphere). At the same time, endoparasitic nematodes are able to enter the roots themselves, breaking them down from the inside.
In anticipation of this threat, fungi will utilize their hyphae, which are the tiny strands that make up their mycelium. Using these strands, the fungi are able to locate and trap both types of nematodes, preventing them from further chewing at the root.
The fungi also receive help from, interestingly enough, other nematodes. They aren’t quite the same, though; while the others are parasitic, these are known as predatory nematodes. They, too, dwell in the rhizosphere, but only to eliminate plant-eating threats in the area.
How Earthworms Play a Part
Not every part of this underground battle is microscopic, though. In fact, the humble earthworm will be one of the main lines of defense for your cannabis plant. Parasitic nematodes happen to be a favorite prey of theirs, so they’ll munch up whatever your fungi and other microbes can’t catch. In turn, the waste they excrete contains nitrogen, phosphorus, and potassium (the three vital nutrients we mentioned earlier), along with calcium and magnesium. They also aerate the soil as they move around, ensuring the plant has easy access to the natural fertilizer.
How Benefits Show Themselves in Cannabis Plants
If you’re able to ensure optimal conditions for your soil microbes, you’ll notice it pretty quickly as your cannabis plants mature. Their leaves will be greener and fuller, they’ll end up on the taller side, and your buds will be notably larger and more resinous than average.
Your plant may be able to survive without a healthy amount of microbes, but it’ll look amateur in comparison. That’s not to mention the cost of those seeds adding up, leading you to lose money you could spend on expanding your growing operation. Armed with this new information, you won’t even have to worry yourself with the thought. Just keep those microbes and worms alive, and you’ll be on your way to hefty yields of potent buds!
microBIOMETER®, a rapid, on-site soil test, will help you determine the microbial levels in your cannabis soil as well as the fungal to bacterial ratio to ensure the healthiest environment for optimal growth of your plants.
Soil microbes are tightly bound to and often covered in soil making them very hard to evaluate by microscopy. The special magic of microBIOMETER® is the extraction powder and whisking process that separates most of the microbes from the soil. And during the 20 minute settling time allows the soil particles to precipitate leaving the extraction fluid >95% microbial.
This allows microBIOMETER® to examine 100 – 1000 times more microbes than any other method. When you apply extraction fluid to the membrane in the test card the colored microbes are captured on the surface of the membrane. A cell phone picture of the card is analyzed by the app and the intensity of the color of the microbes indicates their quantity – this is the basis for all laboratory colorimetric tests. We discovered that the fungi in soils are a slightly different color than bacteria, and so the app is able to distinguish between bacteria and fungi.
Click here to see a full video tutorial of microBIOMETER® soil testing.
Understanding Soil Organic Matter and its impact on soil health and microbial biomass.
We are often asked what is a good level of microbial biomass (MB). There is no one answer. The level of MB you can reach is dependent on soil organic matter (SOM.) Soil organic carbon (SOC) is a large part of soil organic matter but SOM is a mixture of Carbon (C), Nitrogen (N), Phosphorus (P), Sulfur (S) and all the other minerals that microbes and plants need.
There are 2 types of SOM: Stable SOM, often referred to as humic matter; and Fresh SOM. Fresh SOM is composed of SOM material recently released from Stable SOM and any fertilizers, amendments or litter. You can compensate for low stable SOM by providing lots of fresh SOM. The key to the efficacy of fresh SOM is that it needs to be nutrient balanced*, i.e. it needs the correct balance of C,N,P, and S. That is where understanding soil chemistry and using the right additives comes in.
Think of SOM as your credit reserve. In spring, the plant starts to grow and puts out exudates that stimulate the microbes to multiply. But these multiplying microbes need more than the sugars that the plant supplies, they need the N, P, S and micro nutrients that are in SOM.
Agronomists often cultivate soil for intensive organic agriculture and those soils contain lots of fresh organic matter. The microbial biomass of these mixtures can read as high as 2000 ug MBC/gram of dry soil. As the microbes and plants in this rich soil die, they become fresh SOM. The amount of stable SOM that soil can store depends to a large degree on the type of soil because storage requires mineral surfaces for attachment and aggregates for protection. If your soil is inherently poor at storing SOM, you will need to rely on fresh SOM to feed your microbes and plants.
We highly recommend that you read the review referenced below to better understand SOM.
Coonan, E.C., Kirkby, C.A., Kirkegaard, J.A. et al. Microorganisms and nutrient stoichiometry as mediators of soil organic matter dynamics. Nutr Cycl Agroecosyst 117, 273–298 (2020). https://doi.org/10.1007/s10705-020-10076-8
Leeston Pastoral is a 5th generation, family owned farm in New South Wales, Australia. Historically, they have had a fine wool Merino & Hereford cattle breeding operation. Over the last 20 years they have moved to focus on cattle.
The 2019 drought forced them to reevaluate what operation they wanted to continue in. They decided to adopt a more regenerative approach and move from a cattle breeding operation to a cattle trading operation. They now have one large mob grazing holistically using short grazes and long pasture rest periods.
microBIOMETER® has allowed them to quickly, easily and inexpensively record existing benchmark measurements of their soil microbiology and now reassess the effects of stock movements and plant/soil amendments. They are excited to see the new F:B ratio measurement, as they want to make sure the soils stay fungally dominated so they can more effectively create stored soil organic matter.
They were happy to see their microBIOMETER® results showed an almost 30% increase in microbial biomass and fungal to bacterial ratio one month after holistic grazing. Studies have shown that a 1.5x increase in your soil’s F:B ratio can lead to a 3x increase in carbon sequestration. Thank you Adam for sharing your experience with us!
The Sítio Escola Portão Grande is a Brazilian NGO, nonprofit organization which was founded in October 2012.
Sítio Escola Portão Grande hosted students from the Mentoring and Language Acquisition Program (MLAB) for a full day immersion at the farm in Brazil which featured soil testing with microBIOMETER®. MLAB is a mentoring and language acquisition program for Harvard students and Brazilian high school students, with low income and high performance. In addition to mentoring, the program brings foreign students to an immersion in Brazil, exploring themes that motivate them.
The students were delighted to observe the use of microBIOMETER® to assess fertility based on the measurement of soil microbial biomass. It was explained to the students that microBIOMETER® is used monthly to assess the evolution of fertility due to the different inputs applied to the soil, the crops and harvests carried out, as well as throughout the seasons. Therefore, providing a database of great importance to make future decisions. In addition, due to its ease of use, microBIOMETER® also proved to be an good tool to assess the quality of the inputs we produce on the farm, such as bokashi and compost tea, allowing the tuning of the culture media we use for them.
A big thank you to Antonio Feres Neto for sharing this story with us! We love hearing how our customers are using microBIOMETER®.
Types of fungal spores. The sizes vary from microscopic to visable..
Arbuscular Mycorrhizal Fungal (AMF) are dependent on the plant for their food, therefore, they die when the plant dies. Lucky for us before they die they form spores that can live a long time in the soil.
When we have looked at the soil from vineyards in winter it is filled with fungal spores. Pictured here of some of the types of AMF spores. The size of these spores can vary from microscopic to visible.
The spore starts growing when it receives a chemical message from a nearby plant. It has a day or two to reach the plant, enter the root and build a little space called an arbuscule where it can get food from the plant. If it fails at this, the fungi dies. This is why we like to plant seeds with AMF. The plant feeds the fungi because the fungi send out long hair like structures called hyphae that bring minerals and water back to the plant. In fact, scientists have recently shown that the fungi and the plant actually barter with one another, i.e. when phosphorus is low, the fungi gets more food for delivery of phosphorus.
microBIOMETER® measures both fungi and fungal spores as well as bacteria. The lab methods of PLFA and Carbon Fumigation do not adequately measure spores. Standard microscopy also does not adequately measure fungi.
Source: Food Web and Soil Health
The graph pictured here from the USDA website depicts the ratio of fungi to bacteria as a characteristic of the type of system it is in. An excerpt from the article:
“Grasslands and agricultural soils usually have bacterial-dominated food webs – that is, most biomass is in the form of bacteria. Highly productive agricultural soils tend to have ratios of fungal to bacterial biomass near 1:1 or somewhat less. Forests tend to have fungal-dominated food webs. The ratio of fungal to bacterial biomass may be 5:1 to 10:1 in a deciduous forest and 100:1 to 1000:1 in a coniferous forest.”
If you are measuring soil attached to the roots colonized by mycorrhizal fungi, your ratios should be much higher than is shown for agricultural soil. Also the saprophytic fungi population increases when there is a lot of litter for digestion, so you would expect to see different ratios at different times of the year and under different conditions.
The graph pictured below based on USDA website information shows the expected fungal to bacterial ratio for various plants.
Please visit our Using the Fungal to Bacterial Ratio with microBIOMETER® on YouTube for more information on fungal to bacterial analysis.
