The Dirt On Growing Green: What’s This Organic Matter?

By Sunny Kaercher

Perhaps one of the most prolific, and misused, words of the past decade, organic, appears as if it is here to stay.  This article is not about organic cultivation methodologies — or even any certifying body that might confirm that regulate it —  but rather, organic matter in the soil (and/or “grow media”). Organic is the backbone of growing hearty plants naturally, and the key to understanding nutrient cycling.

If you aren’t cultivating via aeroponics or the variety of hydroponic mediums like rockwool, hydroton or lava rock, then you are growing in some form of organic material, and this article is relevant to your operation.

Organic matter is decomposed organic material. And what is an organic material? Essentially, anything carbon-based qualifies as an organic material. A few of our favorite sources for organic material are leaves, grasses, kitchen scraps (aside from animal products & oils), manure, woody materials and root balls. Though they are all carbon-based, each has a unique amount of Nitrogen within their composition. Measured as the C:N ratio (carbon to nitrogen), materials can casually be categorized as either “green waste” (nitrogen-rich) or “brown waste” (carbon-rich).  Anyone who composts probably knows that you want a specific balance of green to brown waste to build rich organic matter. The process of decomposition is beautiful and complex. A fleet of microbes, primarily bacteria and fungi, can take credit for the break down.

Soil microbes consume carbon for energy, and nitrogen for protein (building blocks). As they consume materials, they have the ability of converting it to plant-available nutrients – either in their waste or immobilized in their bodies. Organic matter is valuable as more than just a nutrient source. It has a high water-holding capacity, resists compaction, and encourages aggregation of particles. All of these characteristics benefit both microbes and plant roots.

Referring back to the first Dirt on Growing Green, a native soil comprises of approximately 5% organic matter. However, the soilless medias that are exceedingly popular in the cannabis industry (and traditional horticulture) have much more organic matter/material. Pumice, perlite, or any other rock-based component aside, they are entirely organic materials. Peat moss, coco coir, forest materials, compost, worm castings; they are all carbon-based. All of these materials should be stable (compost as a ‘humus’), meaning they have gone through the majority of the decomposition process. However, there is likely more to be done, and the break down will resume as roots grow and soil microbes thrive. In other words: as your plant grows, nutrients will continue to become plant-available (mineralization).

So what’s the magic recipe of organic matter for growing cannabis? Well, it entirely depends on your situation. But regardless of your situation, if you are growing in organic material, you will want to replenish organic matter often. Either with fresh grow media, or top dressing to integrate the benefits. Top dressing can range from applying humic acids, to mulching, to spreading mature compost. Effectively, you are feeding the microbes so that they can feed the plants. Old leaves turning in to new leaves. What better demonstration of the interconnectedness of this world?