By Cosmos Burnigham

Aa the cannabis industry emerges from the shadows, cultivation practices are evolving rapidly. But some things remain unchanged. Compost and compost products will always remain a core component of intensive

agriculture. Cannabis likes to be fed well and thrives in high-organic matter and free-draining soils, which compost provides in excess. Further, the choice of inputs and media constituents used in cannabis cultivation are particularly important, not only for the plant’s health but also for the humans who consume it.

Nutrient inputs have a tremendous influence on the health and growth characteristics of the plant. Compost provides the plant with micronutrients that significantly enhance the quality of the finished flower. However, because cannabis accumulates heavy metals through its roots, and flowers can be easily contaminated with mold and pathogen spores, choosing an uncontaminated compost free of heavy metals and molds is essential to growing a healthy plant.

The term “compost” gets thrown around a lot, but not all compost is created equal. Compost can be a variable and confusing material. The term can refer to the purest, slowly degraded humic material or to composted municipal “bio-solids” that literally contain human feces. As a farmer who grows for human consumption, you have a particular responsibility to understand what you’re building or buying.

The National Organic Program (NOP) and the U.S. Composting Council are a good place to start. They have defined standards and protocols to describe the differences in compost, but many gardeners are confused by the terminology for the many diverse types of compost products, which can contain potentially hazardous materials. This confusion undermines reputable manufacturers and leaves an open path for shady operators who sell all manner of toxic or contaminated material—presented as the metaphorical silk purse, though a basic understanding reveals it to be a sow’s ear.

Compost is any organic (as a chemistry definition: containing carbon) material that has been decomposed. More specifically, it’s the process of biological organisms degrading a carbon-based substrate. This process may take thousands of years or can be accelerated in controlled vessels so it occurs in days. Composting breaks down base materials to create a more consistent, concentrated, and stable medium as well as increasing the availability of plant nutrients. Meanwhile, the degrading organisms generate natural heat that reduces human pathogens and destroys or degrades the viability of weed seeds.

High-quality compost is essential to agriculture—it increases water retention, improves fertility, enhances biological levels, and increases cation exchange capacity. In order to choose or generate a high-quality compost for your garden, it’s important to understand the common varieties of compost.

“BACKYARD” COMPOST: You likely make this type as it is food waste, yard scraps, and paper products broken down for use in a home garden. Systems range from the old- fashioned compost heap to small machines that fit in your kitchen, using carbon filtration to control the smell. Whether you go high-tech or low-tech, home composting is definitely worth trying. It’s pretty much idiot proof, as long as sufficient moisture and aeration are maintained. Although certain practices are ideal, it’s difficult to go so wrong that the product is unusable. Home composting creates rich material that can be a great ally in enhancing the organic content of soils to support vigorous root growth, while keeping tremendous volumes of material out of landfills.

GREEN WASTE: This is yard waste or landscaping materials delivered to composting yards by consumers and landscaping companies. This material is common and likely part of most locally produced potting soil mixes as well as landscaping supply “compost” products. The fees you pay when you dispose of your truckload of grass clippings help fund the process, and professional composters can generate fairly consistent materials, especially given how wildly variable their inputs can be from season to season. Green waste is commonly available and relatively cheap, making it a common choice for potting soil manufacturers. Contamination is likely, including synthetic insecticides, pesticides, herbicides, and small amounts of trash and fertilizer. Because of the inconsistency and contamination, this author doesn’t recommend green waste for cannabis or any other consumable crop. (That said, some green waste-based composts have been approved for use in organic farming. These mixes are widely used by large industrial and commercial farms and potting soil manufacturers.)

BIOSOLIDS: This is derived from the solid output of sewage processing plants. Reducing waste to a solid form is a positive tactic because it prevents these materials from being discharged into our waterways. The downside is that it generates a concentrated byproduct that must be dealt with. This solid material is routinely applied on conventional farms, sold in bulk to anyone who will buy it, or blended into retail potting mixes and fertilizers. This material definitely can’t be used in certified organic farming. Controlled environments generally do a good job of sterilizing pathogenic organisms, but heavy metals and prescription-drug chemicals can survive the composting process. Plus, biosolids are specifically prohibited from organic production but appear as “natural” in the marketplace.

VIRGIN MATERIALS: These materials (such as forestry materials) make up “premium” composts because they can be chosen in terms of consistency and quality. Reputable manufacturers use these consistent resources in high-quality composts, potting soils, and professional mixes. This material can be used in organic crop production as long as it is composted to NOP organic standards, which prescribe minimum and maximum carbon to nitrogen ratios, composting temperatures, turning and curing times, and limits on pathogen and heavy-metal levels in the final product. Compost made to USDA/ NOP organic standards is free of heavy-metal contamination and has been composted sufficiently to nutritionally support your plants’ needs.

BIOGAS REACTOR OUTPUT: Solids left over from biogas production, see above. Biogas reactors use various inputs such as manure or food waste, which is anaerobically decomposed in an enclosed vessel to capture the methane produced. Increasingly common as alternative energy sources gain popularity, this compost is a consistent material when acquired from a consistent source.

Most of this output is returned to commercial farm fields but some does appear in consumer products. The downside is that the process is managed for maximum output. This means that processors may boost methane production by introducing unsavory materials, such as animal carcasses, into the biogas vessel. This material is difficult to certify as organic.

VERMICOMPOSTING: This is a premium organic fertilizer that cannabis growers have long recognized for its beneficial impact on the plant’s growth and the quality of its yield. This is another exciting and common home process, although it can be done on a much larger scale. Many people misunderstand vermicomposting and believe the worms themselves are consuming and decomposing organic waste and food scraps. Actually, it’s a team effort whereby the worms agitate and reduce the size of the material so smaller biologicals can consume and decompose it. The worms then benefit two times from the primary nutrient source and by securing nutrition from the decomposer. It’s easy and fun to try at home. When the concept is applied to a consistent production system, it can create some of the highest quality organic fertilizer. If you’re buying it, look for the product that’s NOP organic certified.

MUSHROOM COMPOST: This is more of a partial or pre-composting process whereby a future mushroom substrate is partially decomposed before and during mushroom cultivation. This material is commonly available bagged or in bulk. It’s important to buy organic as some cultivators use pesticides for insect control and amend the material with urea to boost mushroom yield.

As we strive to make sustainable choices as gardeners, it’s essential to know what we’re buying and who we are supporting with our money. Compost is powerful stuff when used correctly. Use certified organic virgin compost and compost-based products and leave the green waste for the landscaping. Quality sustainable cannabis is your reward. Happy gardening!