Over the years, through many seasons of trials and tribulations, a seasoned cannabis gardener learns that while the quality of your crop is determined by many factors, some attributes of your cultivation practices matter more than others.

Before we break down the most important variables of high-quality cannabis cultivation, what are the defining parameters of high-quality cannabis itself? Modern testing laboratories allow us to check for the potency of the various cannabinoids including THC and CBD, and for contaminants such as bacteria, yeast, fungal diseases, pesticide residue, and heavy metal toxicity. Besides the cleanliness and potency of cannabis, the other very important factor for most cannabis enthusiasts is flavor and aroma, which are both determined by the levels of various terpenes present in the harvested product.

Great Genetics, Great Cannabis

Anyone with extensive experience will tell you that what matters the most to increase your chances of consistently growing high-quality cannabis is genetics. Even a beginner cannabis cultivator can grow top-shelf product given the best genetics to start with. By contrast, unstable and low-quality genetics grown by the best cultivator around cannot reach the potential of high-quality strains and genetic vigor. Whether you start from seeds or purchase clones, knowing where your cannabis genetics come from and getting them from someone who has good breeding practices and knows how to keep cannabis plants healthy and free of pests and disease will consistently pay off in the long term. Taking clones of your acquired genetics, while still in the vegetative phase of growth and preserving them in a clean and separate growing area, is also a very important step. This ensures that when you do find that special cultivar you can rely on yourself to keep it stocked, healthy, and available for propagation.

Control the Environment

Second in importance when it comes to growing quality cannabis is the environment it is grown in. Outdoor variables can make one outdoor growing season drastically different from another and can lead to bumper crops one season and light or damaged crops during another. High winds, extreme temperatures, soot from wildfires, pollen drift, and unwanted pests and diseases can all wreak havoc on your crop. Indoor gardens and some greenhouses have the huge advantage of practicing a method known as controlled environment agriculture (CEA) to create the ideal set of conditions for cannabis. Using appliances such as horticultural lighting, heaters, air conditioners, inline fans, dehumidifiers, humidifiers, and carbon dioxide (CO2) systems, CEA allows the cultivator to consistently control the variables that produce the best cannabis crops. Taking notes and records of the various environmental conditions found in your garden can be the key to re-creating the success of a previous crop. For this reason, written or digital records of all your environmental conditions is highly recommended to increase your consistency. Indoor gardeners who can control their environment and also supplement CO2 levels would be very wise to seek out information about vapor pressure deficit (VPD). Vapor pressure deficit is the complicated relationship between air temperature, leaf temperature, light levels, and humidity levels that determine what percentage of stomata are open on a leaf’s surface, which ultimately determines the upper limits of how much CO2 a plant can absorb through photosynthesis. Therefore, VPD is what determines a plant’s rate of metabolism and indoor gardeners that master VPD are certain to maximize their harvests.

Red Light, Blue Light

Another very important factor for indoor gardening relating to the environment of your cultivation space is the lighting technology and fixtures used to simulate the full spectrum of sunlight. Older bulb technology was only able to make one dominant color of the light spectrum at a time and required indoor gardeners to switch their bulbs mid-growth cycle from a predominantly blue spectrum bulb to a red/orange spectrum bulb. Thankfully, recent advances in lighting technology such as LEDs and full-spectrum bulbs allow you to customize the spectrum ranges being delivered to your plants and better replicate what light colors plants actually need. One of the first things cultivators noticed when first using full-spectrum light indoors was that individual phenotypes expressed themselves more, and their plants showed a wider range of pigments and colors in their flowers. But perhaps the most significant discovery related to new lighting technology is that cannabis exposed to extra amounts of ultraviolet A (UVA) and ultraviolet B (UVB) light directly increases the plants’ production of the cannabinoid THC. Many growers now supplement extra UVA and UVB lights to take advantage of this theory.

Nutritional Necessities

The third category of variables that still plays an important role in determining the quality of your cannabis crop are the nutrients you feed the plants. Whether it’s mineral-based fertilizer, organic liquid nutrients, or dry soil amendments, the quality and details of your feeding regimen factor into the results at the end of your cultivation. Avoid fertilizers intended for ornamental horticulture made with low-grade ingredients such as urea and ammonia or contaminants like heavy metals. When in doubt, seek out the heavy metal report listed on the label of the bottle such as the Association of American Plant Food Control Officials (aapfco.org) or your local regulatory agency to see the tested parts per million of all the chemical elements in your fertilizer.

Observe, Measure, Experiment

The fourth and final factor for successful cultivation is you. Your skills, common sense, and critical thinking skills all play a role in maximizing the quality of your production. Using empirical skills such as the scientific method to observe, measure, experiment, and create hypotheses goes a long way to ensuring success. One of the most common mistakes, however, is making too many changes to your gardening practices all at once. Such a gardener will never learn which changes created what desirable outcome, or worse, won’t know which changes caused a catastrophe. Make changes slowly and practice the scientific method to dial in your garden. Common sense also goes a long way with cultivation; the best cultivators know you need to pick a single strategy and stick to it by making a string of consistent decisions.

Cannabis Connoisseurs

For some connoisseurs, the most desirable characteristic of cannabis is its wide spectrum of available fragrances and flavor profiles available across a myriad of modern cultivars. The aromas of cannabis are caused by the presence of terpenes, which are the main ingredient of essential oils. More specifically, they are volatile organic compounds similar to alcohol. Cannabis has a diverse list of more than 200 known terpenes that can be present in many different combinations from as few as one per sample to 10 or more in a single sample. One of the discoveries of modern cannabis science is that strains have specific terpene profiles and ratios that are like a genetic fingerprint. Modern terpene testing can even be used as evidence of genetic heritage and to associate the lineage of one strain with another because of similar terpene ratios.

There are many factors to understand in order to increase terpene production. First, the compounds that plants create are called metabolites and they are made from the nutrients we feed the plants and the carbon they transpire from CO2 in the air to make these carbon-based compounds. These metabolites are broken down into two categories: primary and secondary. Primary metabolites are the compounds the plant must have to survive, such as proteins, carbohydrates, and lipids. The secondary metabolites are compounds like terpenoids, phenolics, and alkaloids. Although they may help the plant, secondary metabolites are not required to be synthesized in order for the plant to survive. For a plant to decide to spend its energy and available nutrients building secondary metabolites, it must come close to having all of its nutritional requirements met and all of its work done creating primary metabolites in order to switch gears to terpene production.

How you can apply this knowledge to cannabis cultivation to increase the presence of terpenes is fairly straightforward. Avoid most environmental conditions that cause plant stress, especially high heat and low humidity, because they may shut down the production of secondary compounds altogether. Another commonly practiced theory is to lower temperatures for the last one to two weeks of your flowering cycle which helps lower the evaporation rate of the volatile monoterpene,s which are produced and dissipated out the tip of the trichomes on a daily basis by living cannabis plants. Likewise, curing rooms and drying areas need to have their humidity levels and temperature controlled to preserve as many of the volatile terpenes as possible during curing.