Much like any other plants, when growing cannabis, there are 9 key environmental parameters that need to be adjusted and balanced in order to optimize plant growth and cultivation. These parameters are divided by the root zone, what’s underground, and the leaf zone, anything above ground.
In the root zone, there are four parameters to tend to.
The first is Root Temperature. The roots absorb water and nutrients that help feed the plant, and if kept at an unsuitable temperature, they can become hosts to fungus, they can develop root rot, or even stop absorbing nutrients and water completely, and begin to wither and die. The ideal root temperature that cannabis needs to be kept at is around 75ºF. Provided other parameters are met well, this will aid in keeping away mold and decay while allowing the plant to develop a strong root system perfect for absorbing nutrients and bringing growth.
Nutrients are the next parameter. Plants need soil rich in nutrients to germinate, grow, fight off disease, and reproduce. Growers are still experimenting with the best blend of nutrients, but most include some blend of nitrogen, phosphorus, magnesium, and calcium, whether in their raw forms, sprinkled into water or in soil additives like peat, eggshells, compost, etc.
Water is an obvious parameter that all plants need. It, too, is necessary for photosynthesis. During this process, plants use carbon dioxide from the air and hydrogen from the water absorbed through their roots. The plant consumes the hydrogen from the water, and the carbon from the plant, releasing oxygen as a byproduct. Not enough water and the plant won’t be able to go through photosynthesis. Too much water and the root system can rot, or even suffocate. Of course, water is also used to shuttle necessary materials like sugars and minerals throughout the plant structure.
Plant root systems need oxygen for aerobic respiration. For a hydroponic system, most oxygen used in the root system is in the nutrient solution, or the water supply in the form of dissolved oxygen (DO). If plant roots don’t get enough oxygen, they take in less water, and can no longer absorb nutrients properly. Plants begin to starve from lack of nutrition, roots begin to wither, and plant growth is stunted. Toxins will begin to build up and pathogens can take over and kill the plant.
The remaining five parameters are found above ground, in the leaf zone.
In nature, plants absorb the CO2 that living beings exhale. They use the carbon to either create sugars or to store for growth, and the oxygen is released into the air. In controlled environments, this cycle needs to be replicated by adding CO2 to the air. According to the experts, an ambient CO2 concentration of 400 parts per million is ideal to create a carbon-rich environment in which plants can thrive.
Ambient room temperature is another parameter paramount to plant growth. In order for the Calvin Cycle to occur, a key phase of photosynthesis, temperatures must be within a specific range, 77-86ºF. Too much heat raises the leaf surface temperature (LST) of plants, causing leaves to wilt, halting transpiration, evaporating water out of the leaves and soil, and ultimately killing the plants. There is an ideal range of LST for cannabis, from about 85º – 88º F, at which the first stage of photosynthesis occurs. This stage, known as the Calvin Cycle, is where RuBisCO, a chemical inside plants, strips carbon from CO2 to use in either the creation of sugars or the growth of the plant.
An important factor in maintaining a good temperature is humidity. Plants release humidity through their stomata, sweating out droplets of water. As the water evaporates, it cools the plant and keeps its temperature in an ideal range. Plants produce a lot of humidity, and it must be moved away from the plant. If it’s not, the water on the plant can’t evaporate, and in very humid environments, those plants can become homes to diseases and mold. The ideal range for humidity is about 40-60%. It won’t leave plants dry, but it also helps keep mold and fungus at bay!
Air velocity, the penultimate parameter, is the key to venting humidity, cooling the plant, and enabling efficient gas exchange. A good airflow keeps growing environments fresh, cool and keeps plants in the ideal conditions for photosynthesis. Cannabis cultivators create this airflow by adding venting systems that blow air across their canopies. This has the added benefit of keeping leaf surface temperatures cool, which is pivotal when using old-fashioned High-Intensity Discharge (HID) lighting systems.
Not only do they run hot, increasing ambient room temperature, but HID lights also emit a spike of infrared radiation which is absorbed by the plants in the form of heat. HID users need good air conditioning to mitigate this extra heat. While alternatives like LED will run cooler, and not emit any infrared radiation, this sometimes requires growers to pair back air conditioning and raise the temperature of their grow rooms to maintain that goldilocks zone of 85-88º at which RuBisCO works best.
The final parameter is light. Plants require light, in the form of photons, to begin photosynthesis. The light must come from a specific range of wavelengths, known as Photosynthetically Active Radiation, or PAR. This is the part of the electromagnetic radiation spectrum that is useful to plants and algae to activate photosynthesis and exists within the visible range of light. Every color is used by cannabis, from red to violet, and everything in between, and is absorbed by different pigments in the plant. Features in crops like orange hairs and purple buds are the result of a diverse diet of PAR light. The more PAR light a gets, the better it can photosynthesize.
As the amount of light, a plant gets changes, every other parameter in the plant needs to be altered. When light is at higher intensity, plants will absorb more nutrients and water, consume more CO2, and go through photosynthesis at a faster rate. It’s the foot on the gas pedal of the whole plant growth process. With cannabis, an intense light level is ideal to create more growth, but it will require more of everything else in order for the plants to sustain themselves at that level. Cannabis is a top-of-the-line sports car, meant to be run at high levels of light. It can grow massively and at an alarming speed, as long as its tank is full and there’s someone behind the wheel who knows what they’re doing.