Our industry produces a staggering amount of media waste every day. That stream is engorged by the practice of using media only once. Ongoing cost pressures will eventually drive growers to find every opportunity to reduce expenses and “one-and-done” media will be one of the first things operators look at cutting.
The good news is that the mechanical properties of peat and coco readily lend themselves to reuse. Organic nutrient soil mixtures may require more processing than peat or coco, but they are reused daily in the mainstream world. Media recycling may include root material removal, grading, blending, amending, sanitizing and recharging. If the product is to be reused, it needs to deliver a consistent performance level. Processing large volumes may require specialized machinery, but small-batch recycling may not justify the cost of automation.
Before attempting DIY recycling, seek a recycled media supplier who offers consistent and assured product performance. At the right price, such suppliers can take media off a grower’s worry list overnight.
If such suppliers are not available, growers should look at in-house media recycling options. Remember: Savings on media purchase and disposal are offset by whatever it costs to refresh media for reuse. Smaller operations may find that $200 worth of labor can process a week’s worth of media and is a more cost-efficient option than purchasing 20 bales of new media.
Composting could be a way to reduce media waste, but we usually don’t use peat or coco in composting because neither breaks down readily. Cannabis doesn’t usually produce as much foliage waste as media waste, meaning any composting system would likely require supplemental biomass to be brought in. We recommend talking to a commercial-scale compost specialist to understand space, labor and capital requirements as well as any recommended consumables to make an informed decision.
Block media: Rockwool and foam blocks/slabs are popular media and, compared to peat- and coco-based media, typically have a smaller waste stream. Block growing is so similar to container growing that most container growers can convert to block growing with little change to their table infrastructure and plant layouts. Block waste replaces container and media waste streams, so the disposal bill shrinks immediately.
While the waste volume is lower when utilizing blocks, we find roots grown into the blocks are a significant barrier to reuse processing. Sadly, our recommendation is to not attempt to recycle them. We also advise against incorporating rockwool or foam into field soil as they do not breakdown and cannot be easily removed, if at all, later.
Loose, inorganic media: Fired clay balls, perlite, gravel, crushed lava rock and similar materials are relatively easy to remove roots from, and they can be treated with heat and/or chemicals to kill pathogens, which may be the most important task in any media recycling process.
These media are typically used in ebb-and-flow or trough systems because they do not hold water. Not only is there only a small waste stream from these media, but the small volume of the root balls required in hydroponic systems (often a No. 1 or No. 2 container) means lower media costs per plant compared to a 3-gallon or 7-gallon container of soilless media. With the possibility of reusing these materials indefinitely, they are the cheapest media available...
…except, of course, outside of using no media at all. By setting plant roots in troughs that nutrient solution is run down, the need for media is eliminated along with a huge volume of waste and supply costs.
As opposed to the relative ease of changing from container to block growing, trough systems are different than traditional container systems and have more infrastructure. The payoff is gaining additional space from media storage, handling, clean-up and disposal areas that media may have occupied, and it is an easy system to keep clean.
One difference is that no media means plants can’t stand upright, so they must be supported on a vertical or horizontal trellis. If canopy area is maintained, yields can be expected to compete with upright plant production.
Unlike media, we can’t offer alternatives that reduce fertilizer use to nothing, but it can be made simple. A big plus of peat and organic media is that they hold significant amounts of moisture and can be controlled to limit nutrient solution runoff, resulting in practically zero fertilizer disposal.
Alternatively, trough, deep aquaculture and ebb-and-flow systems involve nutrient solutions being pumped around and used repeatedly. Solutions may be amended to bring them back into specification, but, eventually, the grower must dispose of high quantities of nutrient solution. Fertilizers are regulated in all states and localities. Disposal of a high-EC nutrient solution into a municipal sewer should be done only after confirming it’s legal. Don’t guess or assume, get confirmation of what can and cannot be poured down the drain.
Concentration and dilution are two effective fertilizer disposal strategies. Evaporating waste fertilizer solutions produces a low volume of solid residual salts. Local regulations may allow sufficiently diluted nutrient solutions to be released back into watersheds. Again, check local regulations first.
Leaves, Flowers and Stems: Regulated Waste
Fresh cannabis biomass waste is viewed as regulated material, meaning it requires special handling to keep it from being diverted outside the operation. This includes keeping an audit trail of the regulated material from the moment it is removed from the flower room until it’s disposed. That tracking is a common requirement in legalized states, and while it places a heavy cost on operators to maintain the records, it is a condition of obtaining a license. So, for now, this is a waste cost no one can escape.
Regulated cannabis biomass waste may be disposed of by composting or rendering it inconsumable before disposal in a public landfill. Rendering material unusable is a simple process. Grinding biomass and mixing with media, trash, food waste or other materials turns the regulated material into commercial trash than can go straight into a dumpster. But until then, it is regulated waste and must be securely stored. It may be waste, but it’s special waste, and that means it costs more to dispose of.
Pesticide waste is regulated at federal and state levels. We recommend not looking for cost savings here. In fact, get staff to regimentally follow the label’s disposal directions, and no one needs to worry about pesticide violations or worker grievances for unsafe handling practices.
Log pesticide use. Being able to demonstrate proper and controlled pesticide use is one of the ABCs of cultivation. And when it comes to cannabis, cultivators need to be ready to hand over proof of compliance from Day One.
Waste is not a glamorous topic, but if it is on the expense or regulatory radar, it is worth delving into. Doing so may yield significant savings, avoidance of regulatory issues or even a whole new way to grow plants.