How to

12 July 2021

How Airflow Stimulates Cannabis Plant Growth

Air circulation (or airflow) is one of the most critical components to a successful indoor cannabis cultivation operation. Good circulation has numerous benefits for cannabis plants, such as helping control air temperature, manage relative humidity, carbon dioxide (CO2) concentration, and leaf temperature. In addition, airflow systems play a role in safeguarding plants against pests and mould and strengthen them by recreating some of their natural environmental factors. 

Additionally, a bulletproof ventilation system can protect the cultivator by mitigating the all-too-recognisable scent produced by cannabis plants when flowers develop, ensuring your indoor grow room stays under the radar if necessary during the operation’s most critical time. Read on to take a closer look at how vital air circulation is and how to assess exactly what you would need to install your ventilation system to benefit your plants.

The Importance of Airflow

Cannabis plants require CO2, water, and energy from natural or artificial lights to create sugars such as glucose (a significant energy source for most organisms) and produce oxygen during the process of photosynthesis. To ensure a constant supply of CO2, airflow must be established from within the growing environment to circulate stale air out and bring fresh air in.

This will also allow the cultivator to maintain optimal humidity and temperature levels, so plants aren’t stressed by sitting in excessive moisture or heat from grow lights. Thermo-hygrometers can be used to monitor humidity and temperature at different levels of the plant to provide accurate readings of the environmental conditions.

Regulated humidity levels and temperature provided by airflow will help marijuana plants stay on schedule by absorbing water and transpiring correctly. The information provided by thermo-hygrometers can also inform cultivators of adjustments to make to the growing environment’s airflow as the plants progress through their different growth stages.

For example, clones and seedlings, after germination, prefer a higher relative humidity of 70-80%, while more-developed plants in the vegetative stage (60-65%) and flowering stage (45-50%) require slightly drier conditions to flourish. Proper airflow also strengthens the stalks of cannabis plants, which is crucial during vegetative growth and for supporting large, dense flowers of both indicas and sativa seed types.

Pests such as aphids, fungus gnats, and spider mites thrive in high temperature, high humidity environments, and poor airflow can increase the likelihood of powdery mildew on cannabis plants. By incorporating a ventilation system for airflow into their operation as early as possible, cultivators can control their growing environment and put their plants in the best position to succeed and increase yields.

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Creating Airflow: Fans, CFM, and Exhaust

The basic idea behind a well-ventilated environment is to use a combination of vents and inline, oscillating, and extractor fans to draw fresh outside air into the environment, circulate it around the plants and space and then remove it. Ventilation ducting can be used to connect fans and send the air where it needs to go, keeping in mind that longer ducting will require more powerful fans to push air through. The size and power of the fan to use is determined by calculating the cubic feet of the space by multiplying its dimensions (length x width x height).

Cubic feet per minute (CFM) is a measurement of how much air a fan can move. For example, a 155sq ft growing space will need a fan with at least 150 CFM to properly ventilate it. Ideally, fresh air is circulated into the growing environment every one to two minutes.

The easiest way to create airflow is by using oscillating fans pointed at plants from above and below. If fan strength can be adjusted, a low or medium setting is ideal so as not to cause any breakage to branches or leaves that would disrupt structural integrity and photosynthetic ability. If these settings are still too powerful, aim the fans away from the plants to maintain airflow throughout the growing space.

Cultivators can take their airflow to the next level by installing an exhaust system. This will allow fresh air to constantly enter the grow space, providing their cannabis plants with much-needed CO2. The circulating fresh air will push any old, stale air out of the growing environment, which can be directed outside the space using an extractor fan.

When designing a grow space with airflow in mind, the cultivator should consider negative and positive air pressure. This is because the air pressure inside a grow space is determined in relation to the air pressure outside of it. Simply put, if there is a negative (or lower) air pressure inside a space, then the air outside can flow into it more easily.

Positive air pressure inside a space means the air will have an easier time leaving it but will have more difficulty entering. A negative pressure should be maintained inside a grow space to facilitate the circulation of fresh air. This can be achieved using the combination of an inline fan drawing air inside and an exhaust fan directing it back out (the inline fan should be slightly less powerful than the extractor).

The extractor fan and inline fans should be placed at opposite sides of the growing environment. Better still, install the inline fan as close to the ground as possible to direct fresh air towards the base of the plants. The extractor fan should be situated as high as possible above lights to better cycle out the hot air that has risen.

Fan provides growth promoting airflow for cannabis plants

Airflow tips

The extent of a grower’s airflow setup is determined primarily by budget and electrical power considerations. A passive intake system that requires no inline fan and instead relies on openings in the grow tent to draw air can be attractive to the budget-conscious grower. An activated carbon filter installed just before the extractor fan is highly recommended to allow the warm, odorous air to pass through it before being vented out, mitigating the smell of healthy cannabis flowers as much as possible.

The grower using tents for their crop will benefit from sealing the space as much as they can. This will create an entirely separate space from the outside environment and make achieving negative air pressure much easier for the grower. A completely sealed environment will also prevent mould and dust particles (and tiny pests such as aphids) from entering the space and compromising healthy plants

When building out the grow space, install the ventilation system before lights to minimise any tedious reconfiguring of equipment or damage to expensive HPS or metal halide bulbs. The grower should also keep the climate of their own living space in mind as this will determine the temperature of the air that is circulated into the growing environment. It is best to keep fans running twenty-four hours a day to put plants in the best position to succeed – too much fresh air can never be a bad thing for a cannabis crop.

If the relative humidity in the growing environment is too low after deploying the airflow system, it is a sign that the fans in operation are too powerful for the space. To counter this, the grower can replace their extractor fan and oscillating fans with less-powerful models, as low humidity environments may hinder transpiration. A small humidifier may also come in handy.

Practice good growing environment hygiene by keeping it as clean as possible throughout the crop’s entire life cycle. Avoid entering the space in contaminated clothes and do not smoke inside the growing space.

Airflow systems are highly beneficial for cannabis plants and can be achieved by applying the basics outlined above. By starting with seeds bought from Marijuana Grow Shop, cultivators can grow their crop with confidence and, using the principles of airflow, stimulate their plants’ growth to produce big, full, and resinous flowers.

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Post author
Martin
Martin is a production horticulturist with experience in commercial cannabis cultivation and sustainable farming from his time with Emerald Cup Award-winning farmers Esensia Gardens in northern California's Emerald Triangle.
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