Why do your plants need fresh air and how do they use it?

Ideally in your growroom you want conditions exceeding those a plant would experience naturally. One of these conditions is the provision of fresh air that is rich in CO2 so the plant can perform the maximum amount of photosynthesis possible.

Plants are used to natural environmental exposure, wind, and an endless supply of fresh air. It is obvious that in comparison, the environment of a growroom can be still and stagnant, with a low concentration of CO2. An ongoing stream of fresh air brought from the outside and passing through the growing environment is a must to keep CO2 levels optimized, allowing the plant to perform photosynthesis and boost growth and yield.

Read also: Control Your Grow: Comparing Different Types of Growing Environments

Air Flow in a Closed System

There are some closed-system environments which can be very effective for the right crops. A closed system is an environment that is completely closed to any outside factors including air coming in or out. The air in the grow environment is simply re-circulated using a conditioning unit. While these systems do work very well, even a closed-system expert will tell you that a breath of fresh air in that closed room every now and again does the plants a world of good.

Plants are very susceptible to temperature fluctuations and generally perform best under stable conditions. When growing indoors we are substituting the sun for grow lights so there is a risk of over- or under-heating a growroom.

A ventilation system ensures continuous air flow between the outside world and the indoor grow area. Ventilation systems use a combination of exhaust and intake fans, ducts, and pipes to maintain airflow. This airflow helps to stabilize the temperatures of the indoor growing environment as well as cleaning any dirty, stagnant air in the process.


Illustration of a common grow tent ventilation setup.A common grow tent setup.

Importance of Ventilation

Ventilation systems are also essential for humidity control within your growing environment. Plants work as efficient dehumidifiers naturally by themselves but when growing inside, if your environment is not properly ventilated, you will soon see problems occurring.

With no air movement and exposure to high temperatures, a plant expires water vapor rapidly and there will be nothing to move it away from the plant or out of the air. If left in this state, your growroom will become very humid and damp. This in turn creates the perfect environment for mold to thrive, which can be the kiss of death for your crops and equipment. A ventilation system will work to move the humid air away from the plants and out of the environment. The plants can then breathe and take in more water (and nutrients) through the roots.

Read also: Recycling Heat Between Dual Flowering Rooms

A steady flow of fresh air keeps your medium dry, minimizing the risk of any insect infestations. The use of fans is also beneficial in managing the presence of any flying pests like gnats. By maintaining a breeze, it prevents them from having free access to all your plants as they find it much easier to move around in still air.

Your ventilation system needs to be customized to suit your specific setup, taking everything into consideration such as the species of plant you are growing, the heat and humidity requirements, and the size of the space you are growing in, as well as the changing volume of space as your plants grow.

Ventilation Setups

There are two types of basic ventilation setups: passive and active. A passive system features one extractor fan blowing warm air out of the tent while allowing fresh air to enter through an intake hole or vent. An oscillating fan keeps air circulating and regulates the temperature within the tent. A passive system is a good choice for a small growing environment.

An active intake system is a better option if you have a larger grow tent to ventilate. In an active intake system, an additional fan is used — an intake fan. An intake fan pulls fresh air into the growroom. Most types of growroom ventilation fans can be used for either intake or outtake purposes. A simple in-line duct fan is usually the most effective and popular choice and can be mounted inside or connected to ducting.

Read also: The Symbiotic Relationship Between CO2 and Ventilation

To find the perfect-sized fan you need to consider the diameter and size of the fan. You want a fan that will completely replace the air inside your environment in around one minute and to do this you need to calculate the volume of your growroom. It’s a simple calculation: multiply your growroom’s length, width, and height. This gives you your cubic feet per minute (CFM) number and is the ratio that tells you how much air that fan can move in the space of one minute.

Ideally, you want a fan that has a higher CFM number than the volume of your growroom. This ensures the fan will extract all the inside air in less than a minute.
Fan size is important, too, and needs to be correct to the size of the portals and vents on your growing area. Fan size also determines the size of the ducting you will need.

Ducting in a Growroom

Ducting has a simple yet crucial role. It is a collapsible tube running from your extraction fan, taking the warm, humid air away from the fan quickly and quietly. There are many ducting types available designed to reduce any whistling or noise created by your fans or extraction system.

Wherever possible you want to have the shortest length of ducting running from your extraction fan. This is because the air will cool rapidly once it hits the ducting, and condensation may form, hindering your air extraction efficiency. Likewise, for the same reason it is important that your ducting is hung as straight as possible to avoid any small puddles of water forming in any dips or bends. You will also need to buy clamps to secure the ducting. You are looking to make an airtight, secure seal that will stand up in all conditions for the duration of your grow.

Read also: A Breath of Fresh Air: The Importance of Air Purification in an Indoor Garden

There are additional items that you can add to further enhance conditions and performance like carbon filters, which are great for scrubbing odors. However, starting off with the foundations of ventilation and getting them right is fundamental to your understanding and your future success.

Your indoor ventilation system is just as important as the lighting system or feeding regime. When you take time and pick the right equipment to maintain temperature, humidity, and CO2  levels at a perfect range, your plant’s ability to photosynthesize will not be compromised and your plants will thrive in the optimal conditions needed for fast, strong growth and monster yields.