Growing cannabis can be tricky. We want our flowers to be fragrant and recognizable, but we also don’t want them to smell so much that the entire neighborhood knows. Stealth gardens rely on odor control. If you’re growing a wonderfully pungent cannabis plant from ILGM but want to avoid detection by others, this article will walk you through the process of concealing that conspicuous scent.
It’s unfortunately common for growers to become “nose-blind” to the smells wafting from our indoor gardens. As a new grower, you may not realize that fresh, actively growing cannabis plants have a distinct odor compared to combusted cannabis flowers. This is a fact that law enforcement are wise to. In these next few sections, we will discuss proven techniques and products used by successful home growers to mask the scent of their gardens.
TL/DR
Smells can begin in the vegetative stage of cannabis
Carbon filters are essential for reducing odors exhausted from the garden space
Maintain negative pressure in the grow tent to keep smells from escaping
Ozone generation is harmful to people, pets, and plants
Environmental controls can contribute greatly to odor reduction
Table Of Contents
When Cannabis Plants Smell is an Issue
Proper odor control is a 24/7 concern, even if there are portions of the growing cycle when the smells are less pronounced. Marijuana seedlings don’t produce a detectable odor when growing a few of them in a grow tent at home. However, as the plant matures and temperatures and humidity rise, so do the smells. When growing cannabis, discernable odors can be noticed in the vegetative stage all the way through when you harvest and cure your buds.
Once a plant has significant foliage, the increased transpiration produces a generic floral smell of living plants. The smell may not be easily associated with cannabis yet, but to the trained nose, it can lead to questions and potential problems. The height of concern for any grower is in the flowering stage, when smells tend to be at their peak.
Much of the odor we smell is the terpenes, terpenoids, and other volatile organic compounds (VOCs) from the flowers being volatilized into the air. Terpenes are formed in the bulbous heads of trichomes, which develop during the flowering cycle. The closer the plant gets to harvest, the more trichomes it has, and the stronger the scent outside the grow tent can get.
Controlling Grow Tent Odor Starts with Good Airflow
I grow in a grow tent, as do the majority of home growers. Unfortunately, grow tents are not a truly “sealed” environment. Air comes in and out through open doors, seams, and through the aid of an exhaust fan. Keeping the air moving and cycling through the grow tent is vital to healthy growing cannabis plants and an important step in reducing the transmission of odors.
Airflow starts with circulating fans placed inside the tent to prevent pockets of stale, dank air within the canopy. Circulating fans mix the musty air with fresh air. The exhaust fan extracts it from the grow space while drawing in fresh air to replace it. Good airflow will keep your plants healthy and your grow stealthy!
Depicting the airflow and ventilation system within a grow tent.
The Importance of Negative Pressure in Limiting Cannabis Odors Escaping
Exhaust fans are integral to good airflow. Some growers also use an intake fan to add fresh air within the grow space. For those growers, it is important to understand the difference between positive and negative pressure in the grow tent. Positive pressure exists when air enters the grow tent faster than it leaves. This is undesirable because it forces smelly, untreated air out of the ports and seams before it can be treated to mask odors.
Experienced home growers prefer negative pressure, defined as more air leaving the tent than coming into it. Under negative pressure, all of the untreated (smelly) air inside the tent is sucked out through the exhaust fan and passed through a carbon filter, which we discuss below. Negative pressure is a technique used to prevent untreated air from escaping the grow room, thus increasing your control over cannabis smells.
If you are unsure which type of pressure you have, zip up your tent. Do the walls expand out like a balloon? If so, that is positive pressure. Do the walls suck inward? If so, that is negative pressure, and that is the result we are looking for to help control cannabis aromas.
The Importance of the Carbon Filter and Inline Fan
These are, without a doubt, the most essential tools in fighting marijuana odors from the grow tent. We mentioned using an exhaust (inline) fan above and how it can create negative pressure. The other critical component of the odor-removal process is the carbon filter. If the inline fan expels the smelly air without an attached carbon filter, growers simply move that smelly air from one place to another.
Carbon filters are specifically designed to remove pungent odors. Inside the typical steel drum footprint are little pieces of activated carbon. As the smelly air is passed from the exhaust fan through the activated carbon, contaminants and odors bind to the charcoal-like material through adsorption.
To visually grasp the mechanics of this, think of the relationship between a strong magnet (carbon) and metal shavings (odors). The metal shavings are attracted to the magnet as they enter its field of influence. This is how carbon filters work to remove aromas from the air and protect the privacy of your grow.
Inline Exhaust Fan with Carbon Filter in a Marijuana grow room.
Technologies to Mask the Smell of Your Weed Plants
Having multiple lines of defense for combating pungent grow room odors can be quite helpful for concerned growers who do not want to draw unwanted attention. While a carbon filter is an essential tool for neutralizing odors, other products used in conjunction can help remove or mask any lingering smells. Some of these methods are backed up by science, while others are less credible. There are, however, a few that can be detrimental to your harvest.
Air Purifiers
An air purifier is an excellent complementary tool for home growers who are exhausting the grow tent air through a carbon filter and into the lung room. Air purifiers remove cannabis odors by drawing in air from the room and passing it through a filter or series of filters. An air purifier in the lung room also has the chance to scrub any untreated air that may have escaped from the grow tent.
The most common filters used in air purifiers are high-efficiency particulate air (HEPA) filters, but they will only remove odors if they are carbon- or charcoal-based. HEPA filters are beneficial for capturing dust, mold, and other larger particles. Be sure to purchase an air purifier that is powerful enough to treat the entire room or the benefits may be wasted.
Ozone Generators
Commercial cannabis cultivation facilities commonly use ozone generators but use them differently than a home grower would. Open-air ozone generation poses a few noteworthy risks for home growers. I don’t recommend using them, as the negatives seem to outweigh the positives:
Ozone generators aren’t very effective at removing cannabis odor, but they can often mask the scent of mold and mildew. Depending upon the intensity level of the smell you intend to remove, these devices may need to be left running for hours.
Ozone is harmful to people and animals. You absolutely should not be in the room while using an ozone generator, nor should any pets. It is not safe, and the hazard is not to be taken lightly.
Ozone is phytotoxic, meaning it is harmful to your plants. Studies have shown that elevated levels of ozone can cause visible leaf injury. Ozone also hinders chlorophyll production, and the presence of ozone can lead to lower levels of photosynthesis. Photosynthesis drives growth in the plant, which means the presence of ozone can lead to less growth, worse health, and reduced yields.
Odor Gels and Sprays?
There are two ways of dealing with odor: removing/neutralizing or masking it. The method of operation is the primary distinguishing factor between gels and sprays. Removal of odors is preferred to masking odors, but overall, neither gels nor sprays should be the one and only line of defense for your cannabis grow room odor control.
The leading gel brand is ONA, which is a formulation of various chemical compounds resulting in a product that removes odors. Its website lists it as non-toxic and environmentally safe. ONA gel removes/neutralizes odors by adsorption, absorption, and chemical reaction. Gels are routinely placed in exhaust ducting but can also be used in hallways leading from the grow room or where the main areas of the house adjoin the growing area. Do not place them in your tent.
Sprays, on the other hand, mask odors originating in the grow room. A large problem with this method is that sprays are temporary, and the odor from your grow room is 24/7. The majority of sprays on the market are designed to mask the odor of freshly smoked cannabis, not as an agent of odor control for the grow room. Never spray these products directly on your plants. In fact, I don’t personally recommend spray products at all due to their low efficacy.
Incense
Incense absorbs into everything. It can be used in an emergency to mask smells from your grow tent, but it shouldn’t be used as your regular, everyday form of odor control. If you’ve ever made the mistake of storing your stash in a drawer with some incense, you know how quickly incense can ruin the taste and smell of a good bag of weed.
My favorite way to cover smells quickly (albeit temporarily) is to cook some odorous food that will linger in the home for hours. My “go-to” is bacon.
Cannabis Growing Tips for Odor Control
10 Best Tips For Maintaining A Low-Odor Indoor Garden
Use circulating fans in the tent to prevent stagnant air.
Use an exhaust fan to extract pungent air from the grow tent and run that air through a carbon filter.
Maintain negative pressure in your grow tent.
Keep temperatures below 78°F (25.5°C) as you approach harvest (Heat will cause terpenes to volatilize into the air).
Keep humidity below 60% during flower. (Humid air can carry scents/odor molecules.)
Open your tent(s) in a timely manner; don’t let it heat up by not opening the tent door when the lights are on.
If the temperature in your grow tent is out of control, you can use the dimmer on your grow light to reduce the overall heat signature.
Replace your carbon filters regularly (every six months for most 6” carbon filters).
Grow fewer plants in the confined space (More plants = more smell).
Grow strains with lower aromatic profiles or choose strains with pleasant smells like fruits and berries.
Bonus for outdoor growers: Use companion planting. Place plants with strong scent profiles, like lavender, rosemary, or lemongrass, in and around your outdoor grow. Do your research, though, to be sure you aren’t planting a variety that attracts certain insects, like aphids or spider mites.
Using a Lung Room as Odor Control
Many of us have our grow tents in an extra room, which we use as a lung room. We use active or passive intake to pull fresh air from the lung room into the grow tent. The smelly tent air inside is exhausted through a carbon filter and then back into the lung room.
Additionally, you can use an air purifier in the lung room, but if that is not enough odor control for your comfort level, using another inline fan and carbon filter can help. Simply place the extra carbon filter on the floor in the middle of the lung room and then place the inline fan on top. Turn the inline fan on to a high setting, and within minutes, you’ve passed all of the air in the lung room through this second carbon filter, giving yourself additional odor control. Learn more grow tips and tricks by downloading a free copy of Roberts Grow Bible.
A dedicated space designed to manage the environmental conditions for a marijuana grow tent, also known as a Lung Room.
Conclusion
Proper control over the smells in your grow room is important for maintaining privacy and security. For all the attention we place on choosing our equipment, we should also be as diligent about the aromas emanating from the grow tent. Good airflow, an exhaust fan, and a carbon filter are essential for odor mitigation. Controlling your environment and regularly changing your filters are equally important to the task at hand. More than one form of odor control is always better.
Over time, we become less sensitive to these smells. To keep on top of it, occasionally invite a trusted friend or relative over and ask if they detect any smells. If so, at what point did it hit them—the front door, the hallway, or the edge of the grow tent?
A carbon filter, an air purifier, or a carbon filter, an air purifier, and some gel by the doorway will help growers sleep better at night, knowing that they have taken effective measures to remain undetected by neighbors, delivery drivers, or any other persons you wish to keep your gardening activities from. With so many fire genetics from ILGM, growers can find other less offensive profiles than skunk or petrol.
What measures have you taken to conceal the odors from your indoor garden? We’d love to hear your favorite tips in the comments below.
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