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Composting for Cannabis: How to Get Started |

In the cannabis world, soil is widely regarded as a simple culture centre, one of several options, and is often considered less efficient or micro-manageable than hydroponic systems. But a few gallons of fertile soil can carry an entire ecosystem with benefits that cannot be quantified by an NPK ratio.

Composting is the process by which organic waste such as food scraps and yard waste is recycled into compost, a soil amendment rich in nutrients, live microbes and beneficial fungi. The decomposition process is driven by microorganisms that feed on organic matter, breaking it down into its atomic components like nitrogen, phosphorus, calcium, etc. These elements are suspended in fibrous black humus that looks like earth which can then be mixed with soils, spread as a top dressing or used to make compost tea for watering or foliar spraying.

In this article, we review what compost is, how to make compost, and how compost can benefit your cannabis crop.

Benefits of composting

Composting has myriad benefits for any household, even if the product is not used to feed plants. According to the CNDR, more than a quarter of landfill waste is food and garden waste. Removing these contributors from the waste stream eases the load on landfills and incinerators and reduces waste management costs.

Composting also reduces greenhouse gas emissions. Properly composted material undergoes aerobic decomposition as it is eaten by bacteria that breathe oxygen. But organic matter buried under tons of other waste or sealed in plastic bags suffers anaerobic decomposition, a process of putrefaction carried out by bacteria that produce methane.

The benefits of composting are numerous, including the reduction of greenhouse gas emissions. Photo credit

Compost is also rich in microbial life capable of turning dead topsoil into “living soilpopular with organic gardeners. Living soil contains microbes and fungi that work in symbiosis with the plant through root systems. Some of these microbes, such as rhizobacteria, break down larger or inaccessible nutrients, releasing them for the plant to absorb, and the extra biodiversity creates competition for pathogens, decreasing their chances of infecting the plant. Mycorrhizal fungi live on the roots of other plants, feeding on sugary excretions, but in return the fungal roots serve as extensions of plants, increasing their reach for nutrients.

Cannabis Compost Benefits

Compost can help you grow in many ways. Not only as nutrients, but it can also help reduce costs, while helping to reduce the carbon footprint of the crop.

Soil amendment

Compost is a great addition to soil for any plant, but cannabis growers in particular will find it saves money on everything from soil volume to nutrient and litter costs. watering. Compost is considered a soil-first amendment and a cannabis fertilizer because on a pound-for-pound basis it contains fewer nutrients than concentrated products available at garden stores. But this soft loam will improve any soil it is mixed with. For example, when added to dry, sandy soils, compost improves water retention and solidifies soil structure. When added to clay soils, compost improves aeration and drainage, and softens the soil so that roots can sink in more easily.

Diet and pH

As plants grow, they extract nutrients from the soil, so growing the same plant repeatedly in the same soil will significantly deplete those nutrients, leading many growers to buy more fertilizer until nausea.

A plus — and much cheaper — the solution is on the ground with compost. Not only does compost provide its own nutrients, but the microbial life it introduces will stabilize pH levels and increase nutrient uptake, so resources are used more efficiently.

Microbial life

Mycorrhizal fungi in compost can also protect cannabis plants from parasitic nematodes that would otherwise destroy root systems by feeding on them. The fungal filaments called mycelium that grow around the roots actually prevent these nematodes from gaining access to them. Note: When trying to grow mycorrhizal fungi, do not till your soil. Mixing the soil will destroy any established networks of mycorrhizal mycelium.

How to make compost

Composting can be done from Tupperware Countertop Garden Bins. Outdoor bins are unlikely to attract pests and should not smell if done correctly. All of this microbial life needs warmth and humidity, just like us, so choose a spot that’s uncovered for the rain, but still shaded so it doesn’t dry out in the heat. If a compost pile dries out, it will need to be watered to continue the decomposition process.

What can be composted

Compost is made by mixing or layering two types of organic waste: browns and greens. Browns are dried materials like dead leaves, straw, sawdust, and even paper. Greens are wet matter like fruit and vegetable scraps, coffee grounds, and garden trimmings. A ratio of about 3:1 brown to green is generally recommended, but this is not a hard and fast rule. When the pile seems too wet or smelly, add some dry material; and when it’s dry, add more wet material. The most cardinal sin is adding materials that should not be composted.

What cannot be composted

Meats, including fish and eggs, do not decompose the same way plant matter does and cannot be composted (although eggshells can). Likewise, fats and oils, including butter and margarine, cannot be composted either. Paper towels can be composted, but paper towels that contain oil or meat residue, including grease, cannot.

Cannabis by-product composting

Luckily, just about anything associated with cannabis can be safely composted. Cannabis clippings can be recycled, as well as stems, rolling papers and crutches. And composted ash is a good source of potassium, which keeps plants healthy. Unfortunately, bong water is useless. It’s usually stagnant and full of bacteria that won’t be good for anything, so it can go down the drain.

Image of a cannabis plant growing in soil.

Good news, the cannabis plant is fully compostable! Photo credit

Q-tips impacted with concentrate, such as those used to clean a dab rig, may be composted at the user’s own risk. One of the reasons oils and fats are not composted is that they can attract vermin and rot with a foul odor. But cannabis oil is an organic resin that will probably compost well, albeit slowly. However, many of these oils are extracted with solvents which can be introduced into your compost, compromising the organic integrity of the whole. Producers can assess for themselves the risk-reward ratio of reducing available waste while breaking the compost law.

How to make compost tea

Compost can also be used to brew compost tea. When compost is left to soak, much of the nutrients seep into the water which can then be used to feed plants or applied as a foliar spray. To make compost tea, fill a mesh bag (400 microns or less) with compost and soak in a 5 gallon bucket with an aquarium bubbler or similar aeration system. Leave the mixture for 1-2 days; any longer than that and the extracted microbes will begin to starve. Remove the compost like a tea bag and recycle it in the compost pile. The remaining water is Actively Aerated Compost Tea (AACT). Note: This same process without aeration will result in anaerobic compost teafull of microbes that produce alcohol or acetone, which are not beneficial to plants.


Can I use compost to grow cannabis?


Compost is primarily a soil amendment that will improve soil structure, water retention and biodiversity. But it is also rich in micronutrients and some macronutrients that will nourish your plant.

What type of compost is good for cannabis?

Any compost is good for cannabis, but the best will always be a variety of organic materials. Composts made from single sources like manure or fungi will still provide valuable structure and microbial life, but less diverse nutrients.

What does a cannabis plant need to survive?

A healthy cannabis plant requires light, water and a growing medium rich in nitrogen, phosphorus and potassium; and micronutrients including calcium and iron.

How do you use compost for your cannabis plants? What other cannabis material do you compost? Keep the conversation going in the comments below!

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