Composting Cannabis Waste: Turn Grow Leftovers Into Black Gold

Composting is a fairly easy way to turn cannabis grow waste and kitchen scraps into nutrient-rich soil that keeps your cannabis plants as healthy as possible. Microorganisms break the scraps down and make their nutrients available for plants to take up, so stems, roots, leaves and spent growing medium go back into your grow instead of into the trash.

Get the right organic waste together with bacteria, moisture and oxygen, and you've got a compost pile where bacteria break down the organic matter and generate heat in the process.

Why compost your cannabis waste?

With cannabis cultivation booming, the amount of waste it generates keeps growing. As growers, we have two options: throw the waste out or recycle it into compost. Tossing it can do real environmental damage, like the harmful amounts of methane and carbon dioxide released in landfills as cannabis waste breaks down.

How do you make compost at home?

If you've never done it, figuring out how to compost can seem complicated. It's not: you can compost at home easily and on the cheap. All you need is a composter, which you can make yourself by nesting one paint bucket inside another, plus red wiggler worms and, optionally, bokashi (a fermented bran starter), and you're on your way to growing organic cannabis.

What waste can you compost?

The goal is to break down organic matter, and fruit and vegetable scraps are a great place to start. Broadly, there are two kinds of organic material: greens and browns. You need a balanced ratio of the two for beneficial microbes to thrive.

Cannabis grow waste includes plant stems and roots, used growing medium, dead or unviable plants, plus seeds, buds and leaves that can't be used because of disease or poor quality.

Cannabis plants need both macro- and micronutrients, so here's the waste you can recycle into compost for your weed, and what each one brings to the pile:

Water:

The mix should be moist but not soggy. To check, squeeze a handful: if it drips, it's too wet. If you can't get any liquid out, it's too dry. Ideally, a firm squeeze should give you just a few drops.

Oxygen:

Oxygen is crucial, because the microbes that do the decomposing die without it. If the mix is too wet and pasty, air can barely get in.

Nitrogen: 

These are the materials that feed protein to the microbes, also known as greens. They include kitchen scraps, fruit, vegetables, grass clippings, manure, coffee grounds, tea leaves or tea bags, fresh green leaves and fresh trimmings.

Phosphorus: 

Sources include manure and eggshells (which are mostly calcium, with a little phosphorus).

Potassium: 

The best-known sources are banana peels, cucumbers and cabbage.

Carbon:

Also known as browns. Common ones include dry plant material (leaves and stems), straw, wood ash, cardboard, paper, sawdust and hair. Skip paper or cardboard with colored inks, and make sure any wood ash or sawdust is free of oils, paints or other chemicals.

Heads up: organic waste attracts flies and cockroaches that can lay eggs in your compost bin, so you may want to look into natural repellents or companion plants. Or just put a lid or some mesh screen on top to keep them out.

Keep adding fresh plant matter and dry leaves to the bin little by little.

When the mix takes on the classic look of finished compost (crumbly, with no recognizable bits of the original plants, dark brown and with a faint earthy smell), your organic compost is ready to mix into your growing medium and work as a homemade fertilizer for your cannabis.

If your compost is fairly young, don't use more than 30% of it in the mix, because it can shift your soil's pH significantly.

What organic waste should you never compost?

When composting organic waste, leave out salty preserved foods, diseased plants, dog or cat poop, grease and anything containing chemical residue.

Fish, meat, dairy, oils and sauces can technically go in the composter, but we don't recommend them until you've got some experience under your belt, since they're a magnet for rodents and they stink if fermentation and breakdown aren't stable.

Benefits of composting

The benefits of compost are many. One of the biggest is that composting is environmentally sustainable. It also gives you a useful way to reuse organic waste. And beyond growing organic weed, composting has these perks:

• Growing cannabis with homemade, 100% organic compost may help bring out the aroma and flavor of your buds.
• Homemade compost acts as an organic soil conditioner, improving soil structure and boosting and diversifying its microbial life.
• Homemade organic compost cuts down on how much fertilizer you need, since it supplies trace elements plus macro- and micronutrients that feed your cannabis plants.
• Compost matters because it helps soil hold more water, which is huge for plants that suffer from water stress.
• Compost that's over a year old, or mulch, helps keep weeds (the unwanted kind) in check and shields the soil from harsh sun that kills off part of its bacterial life.
• Besides feeding the soil, organic matter feeds earthworms and helps them multiply, and they do wonders for your plants.
• Roughly 40% of the weight of a household trash bag is organic waste, which usually ends up in landfills. If it isn't handled properly there, it can contaminate soil and groundwater and also produces greenhouse gases.
• Composting organic waste turns trash into a great resource for fertilizing your garden.

Composting cannabis plant waste: what to keep in mind

When we talk about cannabis waste today, we might mainly picture big industry, but small home growers can grow sustainably too, making their own compost for weed. For that to happen, we have to take care of our organic waste.

Good for you as a grower and good for the planet

That's especially true if you grow for the cannabis industry or are looking for sustainable ways to dispose of plant waste. Besides improving plant and soil health, composting is a responsible way to reuse plant waste while shrinking your carbon footprint.

These soil improvements happen gradually, but over time they can lead to stronger plants and bigger yields.

Follow cannabis waste rules and protect the environment

In California, cannabis waste is regulated, and anything that has come into contact with THC is treated as "regulated waste." Composting lets you reuse leftover cannabis plant waste and other organic material while staying within the rules. That way, you can dramatically cut the amount of organic waste that ends up in the trash.

Push for sustainable growing practices

Composting also cuts down on the chemicals you use on your plants. Practices like these can even bring in more business. As legalization keeps spreading worldwide, cannabis consumers are more and more curious about how their weed is produced. Following current trends, a lot of consumers switching to natural products may prefer organic fertilizer and organic cannabis.

It's no surprise that the booming cannabis industry generates a serious amount of plant waste. The sector is under scrutiny over how it disposes of that waste. From cultivation to processing, every part of the industry contributes some amount of waste and organic byproducts.

Now you know what compost is good for and that, really, there's no single best compost for cannabis; the trick is just to do it right and help the planet.

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