Super Soil #3: All About Those Mighty Microbes

Want to keep your soil healthy and nutritious? Here’s a little secret: it’s all about the microbes.

May 15, 2016

It’s time to get scientific. The last Super Soil segment gave you a recipe for the optimum marijuana soil. Now, this segment will tell you how to keep that soil healthy and nutritious. Here’s a little secret: it’s all about the microbes. All plants, including the marijuana plant, rely on soil microorganisms to stay healthy and strong. If you want to understand how your plant interacts with creatures your soil, read on! 

All about microbes

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Plants have been around on this earth much longer than humans have. So, they’ve had plenty of opportunities to learn to use their environment to their advantage. One way they have done this is through developing complex relationships with microbes inside the soil. Research over the past 20 years or so has found that plants have much more conscious interactions with soil microbes than you might expect.

No, plants don’t have a brain or think in the ways that humans or animals do. But, plants actually secrete different chemicals to manipulate the environment around them to their advantage. Seems pretty smart, don’t you think?

One of the primary examples of this is their ability to send out sugars. Plants secrete an incredibly wide variety of sugars through their roots. These sugars are known as exudates. Exudates are used to attract sweet-loving microbes to the plant roots. These microbes then provide the plant with the nutrients that it needs to grow and survive.

Soil Doctor Doug Weatherbee explains this process best in an interview with Sustainable World Radio:

“Individual bacterium are all little pockets of minerals and nutrients. They’re little bags of fertilizer. Nutrients are a byproduct of the healthy reaction between a plant and microorganisms.

So here’s a situation where, if I’m a plant and in this given instance right now, what i need is some selenium and then a second later I need some boron, and a second later I need some nitrogen, and so on. What I’m going to do is I’m going to be secreting sugars, different sugar molecules, that are going to start attracting the types of bacteria that have high levels of selenium one moment, high levels of boron the next, and high levels of nitrogen the next.”

Creating cannabinoids

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The plant uses these nutrients to create secondary metabolites. Secondary metabolites are chemicals that the plant uses to attract beneficial insects, deter pests, protect itself from disease, fend off predators, and communicate with its environment.

THC, CBD, and other cannabinoids are all secondary metabolites. In fact, the marijuana plant creates over 400 different chemical compounds. By being aware of the microbes in your soil, you can help your plant produce more of these chemicals. This is great for medical growers. Here’s the catch: we don’t know which microbes encourage the production of terpenes, cannabinoids, or other secondary metabolites.

Soil expert Dr. Elaine Ingham has the answer to this problem. She explains:

“We can’t even begin to put a name to almost all of the bacteria and fungi that are down in the soils. We can’t grow them on any laboratory medium. We don’t know exactly what they do. So, if you don’t know what species of bacteria or fungi are actually doing, really our approach to dealing with this system is that we need to maximize all of the diversity that we can possibly get in there, and let your plant start choosing those organisms that will do the work for them.”

If you want to make great soil for your plant, you’ll need to provide a full diversity of microbes. This includes bacteria, fungi, and other simple organisms. Cultivating healthy microbes has a wide number of benefits, the most important being:

  • Disease suppression
  • Increases nutrient quality of plants (great for dietary cannabis and edibles)
  • Better flavor and aroma
  • Abundant cannabinoids

Good microbes vs. bad microbes

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With over 75,000 species of soil microbes out there, there are bound to be beneficial ones and harmful ones. Fortunately, it’s actually quite easy to encourage the good ones and discourage the bad. All you need is a little oxygen.

Most harmful microbes grow in anaerobic environments. Anaerobic means without oxygen. Once they’re exposed to oxygen, they can no longer grow. Making sure your soil can breathe will keep pathogens and diseases at bay and encourage beneficial microbe growth.

  • Here are ways to provide oxygen to potted plants:
  • Add a little perlite, vermiculite, or tree bark to your potting soil prior to planting
  • Only water when the soil is completely dry, then drench
  • Choose breathable fabric pots over plastic (Smart Pots)
  • Aerate your water prior to watering

Aerating your water is also a good way to help clear out impurities that may harm your plant. Most specifically chlorine, which is often put into tap water. The best way to aerate is with an air stone and aquarium pump. But, at the very least give your water a good shake before giving it to the plant.

Adding worms

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Worms are nature’s aerators. As they pop in and out of the ground, they bring vital oxygen into the soil. If you’ve planted in a raised bed outdoors, adding some worms into the plot will introduce oxygen into your soil, keeping anaerobic bacteria at bay. As a bonus, they leave behind worm castings which just happen to be one of the best fertilizers around.

If you’re lucky enough to plant outside directly in quality soil, adding some extra earthworms to the area is a good idea. Though many professional growers might cringe at the idea of planting marijuana directly in the ground, it’s actually highly beneficial for the plant. The downfall is that your yield might not be as nice until you can build up the quality of the soil through continuous planting over time.

While research has not been done with the cannabis plant, plant roots actually travel much farther than you might expect. According to Dr. Ingham, the root systems in strawberries like to go about five feet deep into good soil. Cannabis is a much larger plant, so we can make an educated guess that roots probably travel deeper than that.

The deeper they go, the more they access a diversity of microbes which the plant uses to create nutrients. The more beneficial microbes the plant can access, the better it’s able to defend itself from pests. Of course, you may still need to intervene against pests that the marijuana plant may attract.

How do you provide microbial diversity?

Whether you’re growing in containers, raised beds, or in the ground, there are a few ways to improve the microbiology of your soil. Here are some basic things you can do to encourage microbial diversity:

Pick quality compost

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No, it’s not helpful to just add your food scraps directly to your marijuana soil. When it comes to compost, things can very easily go awry. Compost can actually breed harmful pathogens and microbes if done incorrectly. You won’t want to risk your crop by adding poor quality product. Unfortunately, there are a lot of very poor quality composts out there.

That being said, compost is one of the most nutritious and healthy substances to add to your plant. Good compost is full of beneficial microbes and is the closest you can get to providing natural food for your plant. Adding really nice compost means that you can drastically cut back on expensive additives that actually kill off beneficial microbes, creating a cycle of dependence on human intervention to solve growing problems.

Some tips for picking good compost:

  • Always research the source of the compost
  • If it smells bad, rotten, or generally foul don’t use it
  • Try to pick a compost that has a balanced ratio of bacteria to fungi

If you’re making your own compost, Dr. Ingham provides some very specific directions on her website. You can find those directions here.

Inoculate with compost tea

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Other than worms, compost teas may be one of the best tools in any growers toolbox. A compost tea is a natural fertilizer made by soaking some high-quality compost in water and adding in fungal and bacteria foods. This grows beneficial microbes for your plant.

When making a compost tea, aeration is incredibly important. If you do not continuously aerate the tea, the microbes will quickly use up the oxygen and your tea will become anaerobic. has a nice compost tea recipe. You may want to swap out the molasses for some diluted humid acid.

Humboldt’s Royal Gold coco fiber soils are inoculated with compost teas in the moments prior to packaging. However, you’ll want to spray the tea on your plants every week or two. Make a new tea each time, as the tea must be used within 2 hours after turning off the aeration motor.

For an incredibly potent natural fertilizer, you can also make worm casting teas. This tea is incredibly rich in nitrogen, phosphorus, and potassium (NPK). Nutrients are locked inside of the castings. These nutrients are released when bacteria and other microbes eat the castings. So, you’re providing a powerful natural fertilizer as well as the microbes needed to break it down with this tea. A nice resource on worm teas is found here.

Add bacterial foods

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Bacteria love to eat sugars and carbohydrates. To encourage bacterial growth you add these foods to well-aerated soil. The most common is molasses. Some people also use natural fruit preserves. These foods should be diluted in water before application.

Add fungal foods

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There are a couple of great fungal foods. The best is humid acid, which can be purchased at most grow shops or gardening stores. You can also use fish hydrolysate diluted in water.

You can also add mycorrhizal fungi to your soil mixture before you plant. 85 to 95% of plants form beneficial relationships to mycorrhizal fungi, so make sure you have some in your soil!

Things that harm soil microbiology

Just as there are ways to encourage microbial growth, there are also ways to drain your soil of nutrients. Unfortunately, some of the most common growing practices can actually hinder soil microbiology. Here are a couple of things to be weary of:


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Though many love Epsom salts for gardening, applying too much salt actually sucks water away from tiny-celled bacteria and kills them. Other salts found in inorganic fertilizers do the same thing. When you’re buying products, read the ingredients and avoid products that contain salts.


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This is really only relevant to people who are planting directly in the ground. When you till soil, the blades of your plow drastically decrease soil microbiology. It does this in two ways:

  • Tilling chops up larger fungi and simple organisms, leaving only bacteria
  • Tilling compacts the soil, creating an anaerobic environment

After you till, the top layer of soil might look nice and fluffy. Yet, the moment you apply water, the soil compacts and drastically limits oxygen. Because you’ve tilled, you probably killed off many of the earthworms that would have otherwise aerated the soil for you. This lack of oxygen combined with any plant material you tilled under creates the perfect breeding ground for harmful bacteria.

Rather than till, you can use mulch mixtures to smother any weeds in the area you want to use for growing. If you’re able to plan ahead and put down this mulch in the winter, then you’re golden. A good resource on no-till gardening can be found here.

If you do need to disturb the soil to break up compaction, it’s best to do so in the winter to let the soil rebuild again before you plant. Cover the broken up soil with high-quality compost, reintroduce good bacteria with compost teas, and cover the area with a layer of mulch. You’ll also want to reintroduce earthworms after the last frost.

As we mentioned in the first segment of this series, there are a lot of different philosophies about how to best grow cannabis. Cultivating microbial health is one way to work with nature to get great results. When you rely heavily on additives and inorganic fertilizers and pesticides, you sacrifice the diverse expression of essential oils and other plant compounds.

However, if you’re looking to quickly create a high-yielding crop, many growers would prefer to use other more commercial growing methods. Regardless, creating healthy soil is a surefire way to grow healthy, happy plants.

Do you have any organic cultivation tips? Share them with us onsocial media or in the comments below.

May 15, 2016