Did you know that most peat-based and coco-based growing media products are not sterile? Manufacturers might promote their products as sterile and/or inert, but when those products include organic matter that comes from nature, it’s impossible to guarantee sterility.

The truth is both peat and coco are always laced with some degree of biology and are susceptible to host microorganisms and microbial activity at any time.

Let’s take a closer look at why peat- and coco-based growing media aren’t sterile and will always contain some amount of microbial activity.

Peat-Based Growing Media – “Essentially Sterile” and “Relatively Inert”

Peat-based growing media, including peat bricks, are often touted as “essentially sterile”, but this is a misconception. Peat, which originates from natural bogs, cannot be sterile or essentially sterile for two main reasons: exposure to environmental factors and the harvesting process.

Peat Comes from Nature and Contains Microorganisms (Even after Sterilization)

Peat is formed in bogs, which are wetland ecosystems where Sphagnum moss and other plant materials accumulate and partially decompose over thousands of years. These bogs are open systems exposed to various environmental elements, including precipitation, wildlife, and microbial activity.

Peat bogs have acidic and anaerobic conditions that limit the growth of many pathogens and weeds but also contain a variety of microorganisms (including bacteria and fungi) that thrive in these conditions.

Keep in mind, not all of the microorganisms that make peat unsterile are necessarily bad. There are many beneficial microorganisms that are essential for healthy plant growth. These microorganisms include bacteria and fungi that help maintain a balanced ecosystem within the peat. Sterilizing peat would eliminate these beneficial organisms, which could lead to a biological vacuum easily filled by pathogenic fungi. Therefore, peat is not sterilized which is why some growing media manufacturers refer to it as "essentially sterile".

It's important to understand that complete drying doesn't sterilize peat entirely. However, it can act as a partial sterilization method. This partial sterilization may reduce the overall microbial load but doesn't eliminate all microorganisms.

Additionally, even when peat undergoes sterilization processes like steam sterilization or gamma irradiation, it’s not completely free of microorganisms. Studies have shown that gamma irradiation at a dose of 50 kGr does not sterilize peat completely. These processes reduce the microbial load but don’t eliminate all microorganisms.

Peat Harvesting and Processing Affects Sterility

The process of harvesting peat involves draining the peatland and removing the peat from the bog. This process exposes the peat to air and other environmental factors, leading to oxidation and changes in microbial activity.

The peat is typically piled on the edge of the bog before being transported to factories for processing and packaging. During this time, it’s further exposed to soil, air, and potential contaminants. For example, the drying process of peat blocks affects their sterility in two main ways:

Exposure to Air and Soil: As peat blocks dry, they’re exposed to air and soil, which can introduce various microorganisms. Manually turning blocks for even drying further increases this exposure.
Microbial Activity: Drying alters the microbial environment within the peat. As water is removed, the microbial activity changes, potentially reducing some microbial populations while allowing others to thrive. This change in microbial dynamics means that while some pathogens may be reduced, microorganisms may still be present.

When harvested peat is transported to processing facilities, it undergoes several steps that further impact its sterility. For instance, mechanical handling and air exposure during the screening and milling, blending, and packaging processes can introduce more contaminants and microorganisms.

Coco-Based Growing Media – Inert but Not Sterile

Coco-based growing media, including coco coir bricks, are derived from the fibrous husks of coconuts. Many cultivators mistakenly believe that coco coir is a sterile medium free from contaminants, but this assumption is incorrect for two primary reasons: natural exposure and harvesting and processing practices.

Coco Comes from Nature

Coco coir originates from coconuts, which grow outdoors in tropical environments. As a result, the coconut husks are naturally exposed to various elements both externally and intrinsically, including:

Microorganisms: Coconuts growing in the wild are exposed to diverse microbial populations, including bacteria, fungi, and protozoa. These microorganisms can inhabit the coconut husk and remain even after processing.
Insects and Pests: The natural environment also exposes coconuts to insects and pests, which can lay eggs or leave residues on the husks.
Environmental Contaminants: Dust, dirt, and organic matter from the surrounding environment can adhere to the coconut husks.
Organic Composition: As an organic material, coco coir naturally supports microbial life. The nutrient content and structure of coco coir can provide a hospitable environment for bacteria, fungi, and other microorganisms to thrive.

Coco Harvesting and Processing Affects Sterility

Coconuts are typically harvested from trees that grow in outdoor environments, exposing them to various natural elements. The harvesting methods can vary depending on the height of the trees and the intended use of the coconuts, but the end result is the same regardless of the method used – coconuts are exposed to potential contamination from soil, insects, and microorganisms present in the environment.

Once harvested, the coconuts undergo several processing steps that can impact the sterility of the resulting coco coir. During the cleaning and de-husking step, the outer husk of the coconut is removed, which can introduce contaminants if the tools or environment aren’t clean.

Next, the husks are soaked in water to soften them, which can introduce waterborne pathogens if the water source is contaminated. Furthermore, it’s important to note that much of the coco coir used in growing media is sourced from suppliers in India and Sri Lanka that don’t have the same environmental requirements for water testing that the United States has.

Finally, the husks are dried, typically under the sun, which helps reduce moisture but doesn’t eliminate all microbial life. Inconsistent drying can even lead to potential mold growth.

Coco coir is not typically sterilized but it can be put through a sterilization process using heat or chemicals. Heat sterilization can effectively kill pathogens but not all microorganisms. The alternative is chemical sterilization, but it requires complete rinsing to remove the chemical residues that can be harmful to plants.

Key Takeaways about Sterile Growing Media

While peat and coco coir are effective growing media, neither is inherently sterile. Natural exposure, the harvesting and processing methods, and the intrinsic properties of peat and coco all contribute to potential contamination.

The best solution for cultivators is to use a peat- or coco-based growing medium that has the right diverse microbial communities to optimize plant health and yields and is proven to be clean.

The only truly clean growing media that contains the beneficial biology cannabis plants need to thrive is bio365 media, and we have the patents and proof to back it up! Contact us to learn more or start a trial.

bio365 blog

Debunking the Myth that Peat- and Coco-Based Growing Media Are Sterile