Living Soil vs. Hydroponics
Whether it’s growing tomatoes or cannabis, indoors or outside, there are a plethora of styles, methodologies, and products one can use to cultivate a plant. With the rise of cannabis growing and a new wave of first-time growers and enthusiasts entering the industry, there is a wealth of knowledge online and in books to start one out. But what is the method for growing your plant, or to reduce waste, and what would be best for your own facility?
Cannabis is a temperamental plant; if you have ever spoken with any seasoned grower, they will tell you growing cannabis is not as easy as it looks. Even though this “weed” from the Eurasian steppe will practically grow anywhere, as in the case of hemp (Cannabis sativa L.), its more selectively bred cousin, what people know as marijuana (Cannabis sativa, and Cannabis indica), can be much more phenotypically unstable. Light at the wrong time, slightly too much or not enough water, nutrients, or temperature can all change the physical characteristics of the plant. These physical characteristics of the plant, which make up the phenotype, are what consumers and cultivators alike look for. The smell, look, and cannabinoid percentage can all be a product of the slightest variation in your environmental controls. Because your growing environment plays such a huge role in the phenotypic response of the plant, it is important to ask how you are growing and what you are adding or subtracting from the environment and how that directly impacts plant physiology.
Generally, in recreational and medical cannabis cultivation there are two methodologies for growing the plant, hydroponically or in living soil. These two methods are many times also associated with indoor vs. outdoor grows and the scale of the operation. Hydroponic growing is almost exclusively used in an indoor controlled environment or on occasion in a greenhouse. Hydroponics is the process of growing a plant in a “soilless” substrate with the use of water-soluble mineral nutrients usually delivered to the plant, based on a strict schedule. Ideally, in a hydroponic system, the only living thing in the grow is the plant. In the cannabis industry, hydroponically-grown cannabis is arguably the norm with some of the largest grows in the country being hydroponically-produced. Hydroponics is easily scalable and is quickly becoming one of the largest methods for mass cultivation of a specific plant. But there are inherent downsides to growing one’s plants hydroponically.
Hydroponics’ greatest strength is also its greatest weakness; hydroponics allows a grower to quickly respond to a change in the environment or a mistake made in cultivation. This quick reaction time is due to having a substrate that is devoid of all biology and does not retain water; these two factors force you to manage every variable but allows you to react when a problem occurs from nutrients or environmental controls. Hydroponics also suffers from two great problems, high waste and biological vulnerability to pests or pathogens.
Every hydro grower will tell you about the high cost of constantly buying and throwing away spent soil substrate, not to mention the costly impact on the environment to meet the demand for soilless substrates. The practices that are required to make many of these soilless substrates are also damaging to the environment. Rockwool, a common soilless substrate used in the cannabis industry, is made from molten agitated rock that has been heated and blown through a wind tunnel. This process gives Rockwool its airiness but it also creates massive amounts of greenhouse gases and Rockwool, like asbestos, can be carcinogenic when the dust is inhaled, leading to serious health concerns in its use as well. Even coco coir, which is made out of the husks of coconuts, is environmentally unsustainable. Coconuts only grow in southern latitudes under very special conditions. They require at least 7 years before they can bear fruit and use a tremendous amount of water and nutrients when grown commercially. In addition, most of these soilless substrates are manufactured and packaged in China and Southeast Asia, requiring it to be transported to the US leading to more fossil fuel usage. The entire soilless substrate industry is unstable and un-environmental. Its dependence on the consumption of new material is both its greatest financial and ecological downfall.
Why is the cannabis industry so entrenched as a community in soilless hydroponic growing? The answer is more sociological than you might think. Cannabis has been illegal to be openly grown for the last 82 years. So growers throughout the US have been forced to grow in dense woodland and indoor environments in order to evade the law. That is why when hydroponic technology was spreading into the cannabis industry in the late 80’s, it allowed illicit cultivators to grow more plants in smaller spaces in indoor environments. The ability to manage plants effectively in small urban grows had long been a struggle of many original growers. So one of the reasons many in the industry are so attached to hydroponics is the usefulness of the system in smaller, more inconspicuous grows. But now we are in the present; with more entering the legal market, it is important for us to consider if some of the techniques the industry was built on are the “best” way to cultivate cannabis.
When looking at how best to grow the plant in a legal market, why not grow the plant in an environment that simulates cannabis’ natural biome the best? Cannabis grows throughout Central Asia and the Middle East with different cultivars adapted to different aspects of the environment. But in general, like all plants, cannabis grows in the soil, usually in large groups of the same cultivar on the wild mountain slopes of the Himalayas. So when we look at an analog to grow our plant why do we not try to simulate that soil, weather, and environment? Living soil in an indoor facility can facilitate this. The ability to control your environment in an indoor facility and simulate any climate and lighting regime combined with a living soil to symbiotically aid in plant health and growth allows the plant to experience its full potential.
Photo caption: (Soil Food Web, USDA)
A living soil system is based on a revolving web of biological and chemical interaction known as the soil food web. This complex interaction of chemistry and biology both creates all the nutrients the plant needs and also protects it from both biological and chemical stress. Building a good compost with the proper base nutrients creates the right environment for the complex interactions of biodiversity to take place. These nutrients can come from various sources from kelp to malted barley, to chitin, and more. All of these ingredients are ways of imparting both macro NPK and micronutrients to the plant. When nutrients are delivered in this form it allows the plant to uptake all of these nutrients when and at whatever amounts the plant wants based on the transportation of nutrients to the plant by the microbiology of the soil. The beneficial microbiota also allows the plant more defense from pests and infection.
The soil itself with all of the bacteria, fungi, and insects will defend the plant from invasive hostile pests. Beneficial predatory insects in the soil and in the canopy will prey on smaller insects that feed off the plant. Bacteria and fungi in the soil will also naturally repel infestations of competitive, hostile bacteria and pests. These pests are prevalent in the industry and when the plant is grown in a soilless, inert media, the plant and environment have no way of fighting off infestations. The soil, and more importantly the biology in the soil even has the ability to buffer the soil from dropping too far in pH. The soil, most importantly, allows the plant to communicate with aspects of the biology like the mycorrhizal fungi and even other pants to ask for nutrients or signal about an infestation. This communication allows the plant to get exactly what it needs when it needs.
Credit: Yoshihiro Kobae
Ultimately, the loss of direct control over the plants’ feeding schedule is a good thing from a more mainstream hydroponic methodology. There is no flushing because you overfeed, you save money by not throwing away your valuable soil every cycle, and you don’t spend money on costly mineral nutrients. The increased cost saving, waste reduction, and quality of the flower produced place a living soil system as superior to that of a hydroponic system. There are always multiple ways to cultivate but some are not only more effective but more sustainable for the environment.
Kobae Y (2018) High-resolution functional analysis of arbuscular mycorrhizal symbiosis in field crops. Journal of Integrated Field Science 15: 18-21.