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The Importance of Environmental Control When Growing Cannabis

HVAC Environmental Control Systems

Quite simply, environmental factors determine the healthy growth of your cannabis plants.

Dig deeper, though, and you will see that it is way more than that. Controlling these conditions can influence the growth pattern, characteristics, yields, and quality of the buds.

These factors – light, temperature, humidity, and air circulation – also play a role in phenotypes.

Thus, understanding the importance and being able to manipulate the environment is the key to a rewarding harvest.


Overview of Genotype and Phenotype

After decades of pure-line breeding experiments, the famed plant physiologist and geneticist – Wilhelm Johannsen – proposed the distinction between genotype and phenotype in 1909 (Peirson, 2012).

Genotype refers to the hereditary disposition of an organism. Think of it as the blueprint of a cannabis strain, in this case. It is the genetic makeup passed on by the mother plant, which determines its traits and characteristics.

Phenotype, on the other hand, refers to the manifestation of the hereditary disposition. It is the physical characteristics of the cannabis strain that you can observe. The environmental conditions in which a plant grows affect the phenotype and other traits.

Do note that the physical manifestation of cannabis plants is also dependent on nutrients, water, training, and others – not only on the environmental conditions.


Overview of Phenotype Variation

Among a group of plants grown from the seeds of the same mother plant, the contrast in phenotypes is commonly referred to as the Phenotype Variation.

You can categorize these physical differences by height, shape, and weight.

Furthermore, you can also subcategorize them by characteristics, such as chemical profiles (cannabinoids and terpenes).


Why is phenotype variation of significance?

For breeders, environmental controls are how they manipulate the traits of a hybrid. They can, over several generations and through complex breeding techniques, create entirely new strains.

Among commercial growers, consistency is a necessity. In other words, the products they sell need to have the same characteristics. Take, for example. Grown under optimal conditions, the estimated THC level should be 20-23%. Customers who bought this product expect the potency to be the same – today, next month, next year, whenever they make a purchase. In this case, they control the environment to avoid excessive phenotype variance.

For you, who intend to or is already growing cannabis plants at home, phenotype variance is the reason why none of the plants you grew are exactly the same. Even if the seeds all came from the same mother plant and batch, each of them will vary from each other – slightly, hopefully.

If you are planning to clone, the usual advice is to select the best female plant with the most desirable traits. You do that because of phenotype variance, which means that in a group of four plants – for instance – one may possess traits you favour the most.


Environmental Factors When Growing Cannabis Plants


Environmental Factors When Growing Cannabis Plants

Having a better understanding of genotype and phenotype, it should be evident that environmental conditions affect plant characteristics.

As you delve into growing cannabis, it should quickly dawn on you how providing the right conditions is essential to plant survival.

And, if you were to provide the most optimal conditions, then you can expect an increased yield of more flavourful and potent buds.


1. Light

As a general rule, the more intense the light, the larger the plants. Larger plants mean bigger buds. Bigger buds mean a happier you.

You have a few options when it comes to the type of artificial lights. The best lights you can use would be High-intensity Discharge (HID) and modern light-emitting diode (LED) grow lights.

Most cannabis seeds are photoperiod. They rely on light cycles to determine when it is time to begin developing their reproductive system. It is why when growing indoors, the plants receive 18 hours of continuous exposure, followed by 6 hours of darkness – during the seedling and throughout the vegetative stage. Once they are ready, changing the cycle to 12 hours on / 12 hours off triggers the start of the flowering stage.

Note: Some strains, such as Northern Lights, are available as auto-flowering seeds. This type of plant does not rely on light cycles. Instead, they automatically switch to the flowering stage three weeks after sprouting.


HID Grow Light

For decades, the gold standard when it comes to marijuana grow lights is HID lamps.

The two types of HID grow lights used in cannabis cultivation are:

  • Metal Halide (MH). Used during the vegetative stage.
  • High-pressure Sodium (HPS). Used during the flowering stage.


The use of MH and HPS grow lights provides you with the highest yield per watt – 0.5 to 1 gram.


LED Grow Light

Although HID lamps increase the yield significantly, it also comes at a price. For one, you can also expect your electricity bill to increase. Also, they produce heat, which can raise the temperature of the growing area thus increasing the risk of heat stress. In comparison, LED grow lights do not use as much energy nor produce as much heat.

The new generation of LED grow lights are vast improvements, yet they cannot match HID grow lights when it comes to yield – 0.5 gram per watt.


2. Temperature

Cannabis plants thrive in temperatures ranging from 65-85°F (19-30°C). If it is too cold or too hot, problems arise. Low yields of poor-quality buds are the least of concerns. The more pressing concerns are stunted growth and death.

Extreme weather condition outdoors is one factor that affects the temperature in the growing area. So, too, is the heat produced by your grow lights, poor ventilation and lack of air circulation.


3. Humidity

Temperature and humidity are correlated. As the temperature increases, the capacity of air to hold moisture also increases. Hence, controlling the temperature should be in conjunction with maintaining proper humidity.

Young cannabis plants, generally, require higher moisture levels. It should be lowered as the plants go through the vegetative and flowering stages.

The general recommendation for optimal humidity levels are:

  • Clones: 70%
  • Vegetative: 40-60%
  • Flowering: 40-50%
  • Flowering (last two weeks before harvest): 40-45%


Clones and seedlings have yet to develop their root system. Keeping the moisture level high ensures that they receive enough water, through their leaves.

During the vegetative stage and early-to-mid flowering stages, gradually lowering the moisture level is recommended as they have already grown an extensive root system.

During the last two weeks, keeping the moisture level at its lowest is to make sure that moulds do not grow on the buds.


4. Air Circulation

Proper ventilation is necessary so hot air can escape, bringing in cooler air to help regulate temperature and humidity.

At the same time, fresh air coming into the growing area ensures an adequate level of CO2 in the air. Not many are aware that for photosynthesis to occur, the plants need CO2 during the lights on hours.

Air should also circulate within the growing area so that fresh air reaches all parts of the plants. The use of one or more small fans located strategically cast a slight breeze. The movement of the leaves and stems is much like exercise, which helps strengthen the branches and stems.


Cannabis Cultivation Environmental Controls


Cannabis Cultivation Environmental Controls

The stakes are high for commercial cannabis growers. The inability to provide precise conditions at all stages of growth can only result in product inconsistency.

Even worse, it may introduce potentially catastrophic problems – excessive thermal stress, diseases, and pests. Quite possibly, some plants may even turn into hermaphrodites, possibly causing cross-contamination of strains or rooms.

Every large-scale cannabis grow operation would want nothing better than to have the equipment and qualified personnel keeping the environmental conditions optimal. Unfortunately, the demand for experienced engineers outpaces supply.

The cannabis industry in Canada has grown tremendously since legalization. Thus, it is easy to see the licensed producers having difficulties hiring engineers with design experience in their field, and HVAC experience in large-scale cannabis cultivation.

As a home grower, you are concerned with only a few plants. In controlling the indoor environment, as long as you keep it within the recommended range, you are bound to have a rewarding harvest.

In a commercial operation, that is not an option – if the goal is to ensure a 100% success rate and high-quality buds. It is why they use an HVAC system that lets them control the conditions at more precise levels.

Nursery or clone room for cuttings and seedlings:

  • Light cycle: 24 hours
  • Temperature (lights on): 68-77ºF
  • Temperature (lights off): 59-68ºF
  • Humidity: 65-70% RH


Vegetative room:

  • Light cycle: 18 hours a day
  • Temperature (lights on): 71-82ºF
  • Temperature (lights off): 63-73ºF
  • Humidity: 40-60% RH gradually reduced by 5% weekly


Flowering room:

  • Light cycle: 12 hours a day
  • Temperature (lights on): 68-78ºF
  • Temperature (lights off): 59-69ºF
  • Humidity: 40-50% RH


Curing room:

  • Temperature: 60-75ºF
  • Humidity: 30-50% RH


While home growers typically maintain the same environmental conditions, commercial growers base it on the strain. The parameters they use are usually adjusted weekly.


HVAC Environmental Control Systems

Manually adjusting temperature, humidity, and thermal conditions are impractical and highly risky. The results are often inconsistent, ranging from poor to excellent harvests. It is, therefore, in the best interest of Canadian licensed producers to invest in automation – an HVAC controller system.

The ability to provide precise temperature and humidity reduce losses and thereby increase profit by:

  • Increased yields. Automation makes it easy to maintain the right temperature, especially when introducing CO2 into the grow room.
  • Reduce humidity spikes. Removing moisture is more efficient by reducing the coil temperature of the dehumidifier for grow tent at the same time as reducing the rate of airflow.
  • Efficient heat load. The temperature and moisture levels in areas surrounding the grow pods are kept near room conditions.

To this end, licensed producers either have installed or plan to invest in an HVAC environmental control system.

It is only by having precise control over the environmental conditions that they can produce cannabis plants that are nearly similar to each other – consistency.

Apart from reaching their full potential, the plants are also kept safe from diseases and pests.

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