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Hemp

Composting for Cannabis

Compost vs. Commercial Fertilizer

 

Composting is the science of building soil dense with microbial life which supports vigorous and healthy plant growth through bio-chemical reactions and other life processes.  This complex and symbiotic plant-microbe relationship is illuminated in our first issue’s article, “Living Soils”.

 

In essence, composting refers to the decomposition of organic matter and minerals by beneficial micro-organisms into humic acid and bio-available nutrients.  Nutrients feed the plants’ growth processes, while humic acid acts as an electro-magnetic buffer maintaining optimal pH and Electrical Conductivity (EC).  For more details on this buffering process, see the article in our second issue, “EC and pH in Soil and Hydroponic Systems”.  The activities of bacteria, fungi, nematodes, and larger organisms like insects and worms also create a soil structure with excellent aeration and water retention properties, essential for productive root systems.

 

In contrast, widespread use of synthetic fertilizers and pesticides causes the once alive and humic acid-rich topsoil of an ecosystem to completely erode away, leaving dead and compacted soils devoid of available nutrients.  This leads to significant economic and environmental issues.  With all the top soil gone, growth can only be induced with the addition of more chemical fertilizers, thus requiring a never-ending, and increasing financial investment.  Constant disposal of waste both from fertilizer packaging and water run-off, as well as spent substrate from greenhouse cultivation, is costly and increases plastic and chemical pollution which is harmful to humans, wildlife and livestock.  In addition, with plant resistance to disease dependent on pesticides, these poisonous chemicals are released into the atmosphere, increasing toxic reactions and species’ die off.  Organisms which sequester atmospheric CO2 and NO2 gas generated by humans have been destroyed in commercially farmed soils, which cover large parts of the earth.  This fact contributes significantly to climate change.

 

As industrial and pharmaceutical cannabis production expands in Europe, large scale operations will face these same challenges.  Utilizing compost targets these problems at multiple levels.  It can eliminate harmful run-off, use of pesticides, and waste from packaging, and greatly reduces the need to purchase substrate.  These functions translate into immense cost savings, while simultaneously implementing a sustainable, and environmentally regenerative approach to cultivation.

 

Making Compost for Cannabis

 

Compost can have many different recipes which can be thought of as “bio-software” programs designed to meet the specific needs of a cultivation operation.  Based upon the combination of materials and organisms used, virtually any production goal can be achieved.  Depending on variety and growing method, the cycle for industrial hemp and pharmaceutical cannabis is between 2 to 7 months from seed/clone to harvest.  This places cannabis in the category of plants which prefer to uptake Nitrogen as nitrate, or NO3, produced mainly through the metabolism of bacteria.  However, because of the length of the growth cycle and phosphorous needs for flower development, cannabis also benefits from the establishment of a diverse fungal network within the substrate.  The beneficial bacteria, fungi, and nematodes also consume dead plant matter that would otherwise attract pathogens. The best recipes for cannabis are therefore composts with a 50-50, or 60-40 percent split of bacterial to fungal populations.

 

A basic recipe for creating such compost, described by Dr. Elaine Ingham, renowned microbiologist and founder of Soil Foodweb Inc., is as follows: 50% woody materials, 40% green plant materials, and 10% high nitrogen materials.  Woody materials are carbon rich dead materials such as woodchips and hay, green plant materials are fresh grasses, leaves, and plants such as comfrey and other herbs, and high nitrogen materials include bat guano, chicken, cow, or horse and other manures.  One must also add “starter” compost or a “compost tea” brew, which contains the micro-organisms you wish to multiply.  These microbes will decompose your pile of ingredients into a homogenous, nutrient-rich compost. Starter compost can be native topsoil from a thriving forest, or high quality organic compost decomposed with or without the help of earthworms.  Compost from earthworms, who depend upon microbes to digest their food, has been shown to contain some of the most effective nitrogen cycling, and disease-preventing organisms, and is capable of enhancing fruit size and flavor in a multitude of crops.

 

The pile must be protected from rain, and must be well aerated. The materials should be pre-soaked in chlorine-free water for three days prior to pile building.  Stack the materials in layers: start with chunky woody material at the bottom to leave air pockets to ensure proper airflow, then add hay, then add the green plant layer, and finally a thin layer of high nitrogen material and compost starter. Repeat this layering process until the pile is about 1.5 meters high.  The piles can be made individually, approximately 1.5 m diameters each, or for large scale production, the piles are made into 100 m long by 1.5 m wide by 1.5 m high rows, called “windrows”.  A long thermometer and ideally a moisture meter, should be inserted into the center of the pile.  The moisture level of the pile should be kept around 50%; water may need to be added periodically to maintain this level. Once the center temperature of the pile has been between 55-65°C for three days, ensuring that the bacteria are multiplying and are not deprived of water or oxygen, it is time to “turn” the pile by flipping over the top 60% of the pile, usually with a pitchfork.  Do this every three to ten days, constantly monitoring to maintain the 55-65°C temperature range. After 70 days, the pile should be ready: it will be reduced to half the original height and become dark coffee brown and crumbly in appearance, indicating the presence of abundant life and humic acid.

 

This recipe can be further targeted to growers’ needs by inoculating the compost pile with liquid brews of special strains of bacteria and fungi.  For example, bacteria from the genus Azospirillum fix and cycle nitrogen, while Pseudomonas species create soluble phosphorus for plant use. Actinomyces bacteria and Trichoderma fungus consume dead plant materials, out-competing pathogens harmful to plants’ roots.  There are thousands of different bacterial and fungal species which perform a great variety of specialized chemical reactions beneficial to the plant life around them.

 

Application of compost in industrial hemp fields should be done before the planting of each crop.  If the field contains contaminants, composts cultured with certain types of bacteria and fungi will uptake heavy metals and excess amounts of elements such as magnesium, calcium and sulfur, which may have built up through commercial farming practices, and store them safely away from the plant.  Bacteria and fungi can even clean soils of poisons such as arsenic and cyanide.  Collectively, these methods are known as bioremediation.

 

For greenhouse-grown pharmaceutical cannabis, compost can be mixed with coco-peat, pumice, perlite, or other substrates and can also be applied weekly as a top-dressing, during both the vegetative and flowering cycles.  Spent substrate from greenhouse grows can be added to existing compost piles, and regenerated with freshly broken-down nutrients and humic acid.  This recycling process can virtually eliminate the need for new substrate input, greatly reducing the cost and environmental impact of the operation.

 

In next month’s issue, we will discuss the brewing of “compost teas”, aerated mixtures designed to multiply specific microbes.  These teas can be applied directly to root systems, or as a foliar feed, as well as used to inoculate your compost piles and accelerate the decomposition process.

 

By Sama’a Djomehri

 

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