Controlling odour

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One of the most appealing parts of cannabis is its unique smell. Although most growers don't mind this aroma, it can cause a lot of trouble if you need to keep your grow top secret.

A grow room full of flowering cannabis plants creates a strong aroma that is instantly recognizable. So, to protect your cannabis plants you will need to make that smell a non-issue.

There are a few reasons why you might not want the smell of your garden getting out of control: 


The smell of your plants could compromise your security in a few ways. The last thing you want is to make it obvious you have an indoor grow. Even if you can legally grow, the hassles of dealing with legalities is just not worth it.  

Respecting your neighbours

Growers generally don't mind the smell of a cannabis plant in flowering, but that's not the case for everyone. Especially if you like in a complex and have other building near yours.  

Excess odour can be an indication of poor ventilation

Sometimes excess odour can mean that something is not right in your environment. This could be poor air circulation, improper ventilation set up, or excess heat. If you can smell your plants a lot more than normal, you should check your environment for any issues.


What Causes the Cannabis Aroma?

Plants that are in their vegetative stage maintain a very low odour as the plants have not yet begun to produce terpenes. Terpenes are the molecules that are responsible for the cannabis plant's aromatic properties. These terpenes are fragrant oils located within the trichomes of the cannabis. Trichomes are the "frosty" mushroom-like crystals growers love to see on their bud. As the plant transitions into the bloom or flowering phase it will begin to produce flowering nodes and the trichomes will develop. In nature these trichomes serve as a defence mechanism for cannabis plants. The terpenes will give off their smell and protect the cannabis plant from animals or insects.


The Best Ways to Control Odours in Your grow Space

When it comes to odour control, there are few different options. You can either "scrub" the smell out of the air using a carbon filter or you can find a way to cover up the smell. 

For smaller grows of just 1 or 2 plants, you can usually cover up the smell but with larger grows, you will most likely need a carbon filter to scrub the air and make sure you're not leaking any smells that may catch some attention. 

Before you look into odour control methods, it is a good idea to first check your grow environment. 

As mentioned earlier, excessive odour can be caused by a poor environment, heat, or poor air circulation. On top of causing stronger than usual aromas, these issues can also be harmful to your plants.

Check your temperature and humidity first and make sure heat and moisture are not making the odours worse.

You can then check your air circulation. Stagnant air can be smell worse than moving air. You can look into increasing air movement with more fans or more powerful fans.

Once you have checked your environment, you can now look at the ways to help with odour.

These are the main ways of controlling odour in your grow space:

  • Carbon Filter
  • Odour Neutralisers
  • Air Purifiers


Carbon Filters


Carbon filters are by far the best option for controlling cannabis grow room odours. Carbon filters, also called 'carbon scrubbers', have something called activated carbon (also known as activated charcoal) inside. This is carbon that has gone through a process to make it extremely porous which increases the surface area. One gram of activated carbon has a surface area more than 3,000m2.

The activated charcoal uses a process called ADsorb to remove the impurities from the air like odour. This is different to absorption, in which a fluid is dissolved by or permeates a liquid or solid. Adsorption is when molecules attach to the activated carbon and do not actually absorb into the carbon.

With a carbon filter you need a set up where the smelly air is being forced through the filter. The best way to do this is by using a carbon filter and exhaust fan. These two components make up the foundation of your ventilation system. These components along with ducting, work to remove heat and odours out of your room or tent.

The exhaust fan pulls air through the carbon filter, and the carbon filter scrubs the air of odours. The air then gets ducted out of your grow tent or room. This system removes old, stagnant air and allows fresh air to be introduced either passively or actively. 



How to Find the Right Carbon Filter

Step 1: Identify the diameter of your exhaust

Step 2: Match up CFH rating between fan and carbon filter.

Make sure the CFM rating of the carbon filter is the same or slightly higher than the one listed on your fan. This ensures maximum efficiency but also has an added security benefit of making sure your carbon filter is only taking in as much air as it can effectively scrub.


Here are some common carbon filter sizes and their CFM (cubic feet per minute), or in South Africa, CMH (cubic meter per hour)

 Carbon Filter

CMH (cubic meter per hour)

 4" x 12" (100mm x 300mm)


 6" x 12" (150mm x 300mm)


 6" x 20" (150mm x 500mm)


 8" x 39" (200mm x 1000mm) 



Step 3: Install the carbon filter into exhaust system


How to Install a Carbon Filter

Installing your carbon filter is very simple. All you will need is some ducting and rope ratchets to hang them. 

Step 1: Gather your equipment. You will need your filter, rope ratchets and some ducting.

Step 2: Attach the carbon filter to the exhaust fan so that the fan is pulling air through the filter. You can use ducting or simply connect them if they are the same size. The ducting should run from the filter to the fan, then from the fan to outside the tent.

Step 3: Ensure the fan is pulling air from inside the tent to outside.


Odour Neutralisers

Unlike a carbon filter, odour neutralisers don't scrub the smell from the air. Instead, these products are designed to cover up the smell by binding with it so that the smell is neutralised. 

It is recommended that you do not place these products in your grow room or tent with flowering cannabis plants. Strong neutralisers work so well they can actually alter the flavour of your buds over time. They can however be incredibly effective at neutralizing odours outside the grow area.


Air Purifiers

Air purifiers are a less commonly used odour control method for home growers. 

They remove most airborne particles including mould, dust, smoke, pollen, viruses and bacteria, odours. 

An air purifier will help remove some smells from the air, but they are not strong enough to pull all the smells from a grow room.


Some Final Notes on Odour Control

A temperature controlled, fully ventilated grow space with fans and a carbon filter is capable of removing almost all the odours in your grow space. While there are a few options when it comes to odours, the best way to remove them is by using a carbon filter and exhaust fan.


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