What Are Biofilms? [And Can They Help Cannabis Growers?]

For many marijuana growers, biofilms are an imminent threat that they must eliminate ASAP. There is undoubtedly a good reason for this assertion. A biofilm is capable of carrying pathogens that could infect an entire garden. The panic is especially prevalent in growers with hydroponics systems. Harmful bacteria could run riot and destroy months of hard work in a shockingly quick timeframe.

However, there is a school of thought which suggests that biofilms are not necessarily the harbinger of death to a cannabis garden. In certain circumstances, healthy biofilms can boost nutrient uptake and suppress disease pathogens. In this article, we look at what biofilms are, when they are concerning, and how to remove them. We also look at circumstances where they are potentially beneficial.

What Are Biofilms?

They are a collection of one or more microorganisms capable of growing on a variety of surfaces. Examples of microorganisms that form biofilms are fungi, bacteria, and protists. In humans, dental plaque is an example of a biofilm. It is a slimy bacterial buildup that forms on the surface of teeth.

You will also find biofilms almost everywhere in nature. They are on animal and plant tissues, medical devices like pacemakers, and even on metals and minerals. There is fossil evidence of biofilms dating back 3.25 billion years! They thrive on wet or moist surfaces.

They form when free-floating microorganisms such as bacteria make contact with a suitable surface. The microorganism produces extracellular polymeric substance (EPS), a gooey substance, to attach itself. EPS is a collection of nucleic acids, such as DNA, proteins, and sugars, so the microorganisms in the biofilm stick together. Over time, further layers are created, and in some instances, the process leads to an extremely thick biofilm.

However, many of them remain invisible to the naked eye. They only become noticeable once they are allowed to grow undisturbed for a significant period. At that point, they may consist of a brownish deposit, which is noticeable. You may also see it if brown or green algae colonize it.

Eventually, when a biofilm has formed a colony of microbes, individual microbes detach from the surface and move with water or nutrients to find further growth sites.

Why Are Biofilms Harmful?

Indoor gardeners tend to panic when they see the merest hint of biofilm. In many cases, they are right to show immediate concern. Although biofilms often consist of benign or even beneficial bacteria, harmful pathogens also exist. They can spread rapidly through a cannabis garden, especially a hydroponic system. If left alone for long enough, you could find a crop riddled with disease. Some biofilms carry pathogens capable of infecting humans.


Lab testing has revealed the most common human pathogens found in MMJ samples. If you have a compromised immune system, any one of them is potentially life-threatening:

  • Candida: This is a yeast often responsible for causing various fungal infections.
  • Salmonella: Almost 20,000 people are hospitalized annually due to salmonella infection. It can cause nausea, vomiting, diarrhea, and fever.
  • E. coli: This is found in crops regularly, especially those contaminated with fecal matter. Exposure can cause similar symptoms to Salmonella.

Though it is common to have some of these microbes present, it becomes problematic when a group of them form a biofilm. It isn’t easy to remove and is one of the main reasons why cannabis flowers fail microbial tests. For commercial growers, this is a disaster that can ruin them financially.

In your marijuana plants, biofilms with harmful pathogens could cause issues such as Pythium or other root diseases. Algae is one of the biggest culprits, though it is relatively easy to spot. It is usually brown or green from dead chlorophyll.

It is also a waste of time trying to rely on pesticides and other antimicrobial agents. First of all, you reduce the quality of your product. Secondly, biofilm can increase resistance to pesticides and biocides. Indeed, exposure to antimicrobials often triggers it.

Biofilm Is Seemingly Everywhere!

In general, bacteria like locations with a large surface area and lots of moisture. Have you ever seen pink discoloration on a bathtub? That is a prime example of a biofilm. Marijuana flowers retain water and are often dense, a perfect breeding ground for biofilms. They are especially prevalent in irrigation tubing, hydroponic basins, and humidity control systems.

Practically every surface exposed to water is a likely biofilm ‘home.’ This is why cannabis growers need to check their garden thoroughly. Perhaps the biggest risks are the use of antimicrobials and the equipment you use to grow weed.

How to Remove Biofilm in Your Cannabis Garden

If a hydroponic system, in particular, is infected with pathogens, removing the problem is a testing issue. The pathogens in biofilms often cause a recurrence of an outbreak after cleaning. Let’s say root rot infects your plants. The standard method of coping is to remove the infected plants and growing medium. You also replace the nutrient solution in recirculating systems (in hydroponics) and treat the nutrient or water solution in the reservoir.

While the above will undoubtedly remove many pathogens, the biofilms formed on the surfaces of your system will eventually cause a new outbreak. Here is how to get rid of biofilm, depending on your growing medium. We advise against the use of tap water because it may contain pathogens that threaten your plants.

If You Use a Hydroponic System

As a rule of thumb, thoroughly clean your hydroponics system at least twice a year, and every time there is a disease or pest issue. You also have to shut down the system entirely while you clean. If a severe disease outbreak occurs, remove and destroy the infected plants far away from the grow room. Get rid of all substrates and commence full lockdown.

As it happens, ‘elbow grease’ is one of your best weapons. Use a hard brush to scrub every surface. This means reservoirs, pots, grow beds, and NFT channels. You will probably not get rid of all biofilm in this fashion, but you will enable sanitation chemicals to come into contact with the affected surfaces.

Run an acidic solution through the system to get to areas such as irrigation lines that are tough to reach. Do this after shutdown, and you could remove limescale, salt buildup, and even dissolve biofilms. Another useful step involves running hydrogen peroxide or another oxidation agent through the entire system. Make sure you complete the process with numerous rinses using clean water.  Keep biofilms from accumulating via water treatment options such as reverse osmosis and slow-sand filtration.

There is evidence that UV irradiation and ozone disinfection of nutrient solution can reduce the growth of biofilm. Some research teams are currently experimenting with enzymes. These are proteins that alter substrates by breaking them down. Researchers could potentially design enzymes for a specific pathogen and exclude beneficial microbes from the purge. Such products could destroy biofilm and even make pathogens sensitive to antimicrobial agents once more.

If You Use Soil

Although there is a greater risk of spreading in a hydroponic system, biofilms can proliferate in the soil as well. Indeed, you may require a microscope to spot them. A quick and easy way to reduce the risk is to add compost tea. This concoction adds beneficial microorganisms that create useful biofilms. Through this process, the damaging biofilms are unable to compete and eventually lose the battle.

If you uncover potentially damaging biofilm in the soil, use a soil treatment, or replace it entirely. One great way to remove bad biofilm is by introducing earthworms to your growing medium.

Here’s Why Biofilms Are Sometimes Useful

Although biofilms in cannabis gardens often spell danger, they have some benefits too. From a microorganism’s perspective, living in a biofilm has many advantages. Many communities of microbes become more resilient to stressors such as high/low pH or lack of water. The EPS produced by the biofilm may act as a shield against UV light, or prevent dehydration.

There are potential benefits for your cannabis plants as well. Remember, many of the biofilms you see will contain helpful bacteria. These healthy biofilms exist where there are moisture and nutrients and are teeming with diverse microbial life. For example, you may find rhizobacteria, known for boosting the growth of plants. As well as suppressing pathogens, rhizobacteria help your plants increase their nutrient uptake.

Those who have commercial hydroponic systems require vast colonies of the ‘good’ bacteria present in biofilms. They are necessary for disease control options such as slow sand filtration. If you have an organic hydroponic system, such microbes are also essential. Biofilms can develop on living and non-living surfaces. This is why you may find them on filters, reservoirs, pumps, and drippers. Once again, beneficial biofilms keep harmful pathogens at bay.

If you have an aquaponic system, you will probably know that biofilms (known as biofilters) are encouraged. The desire is to ensure bacteria such as Nitrobacter and Nitrosomonas are included. This is because they turn organic material from fish waste into nutrients that plants can consume.

Final Thoughts on Biofilms in Your Cannabis Garden

There is no question that biofilms are potentially a hazard in any marijuana grow. When they contain pathogens, they are capable of causing devastation to your entire crop. Biofilms are particularly hazardous in a hydroponics system because the speed at which an infection can spread. These damaging bacteria can also continually re-infect your garden if you fail to clean your entire system thoroughly and regularly. An outbreak of Pythium, for example, is a nightmare scenario, particularly for commercial growers.

However, it is also a fact that biofilms can contain beneficial bacteria, as well. If you grow your cannabis in soil, it is easier to deal with harmful biofilms than your hydroponics counterpart. Regardless of whether you are a large or small grower, it is essential to pay attention to your crop as much as possible. It is also unwise to try and destroy biofilms with disinfectants. This process could kill beneficial microbes needed to ensure your growing area remains in good shape.

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