Cannabis Grow Tent Smell Control Guide

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

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! 

An explanatory image highlighting the patterns and methods of maintaining proper air circulation in a grow tent.
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.

Carbon Filter and Inline Ventilation Fan
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

  1. Use circulating fans in the tent to prevent stagnant air.
  2. Use an exhaust fan to extract pungent air from the grow tent and run that air through a carbon filter. 
  3. Maintain negative pressure in your grow tent.
  4. Keep temperatures below 78°F (25.5°C) as you approach harvest (Heat will cause terpenes to volatilize into the air).
  5. Keep humidity below 60% during flower. (Humid air can carry scents/odor molecules.)
  6. 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.
  7. 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.
  8. Replace your carbon filters regularly (every six months for most 6” carbon filters).
  9. Grow fewer plants in the confined space (More plants = more smell).
  10. 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

An auxiliary room created to maintain and control the climate within a marijuana grow tent.
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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43 thoughts on “Cannabis Grow Tent Smell Control Guide”

  1. Are there grinders on the market that grind an ounce at a time? Most only do a few grams. if you are making oil or tinctures you need a bigger volume. Don’t want a $2000 unit though.

    Reply
  2. Ozone is new????? This was the best way in the 90s to eliminate smell. I dont recall seeing a carbon filter before 2000.

    Reply
  3. I go to the local compost recycling site and get the stinky most robust mulch and spread throughout my property with a grass seed Spreader. Neighbos think the mulch stinks. GREAT Luve in NEWVA be Grow all crops outside, harvest now

    Reply
  4. I love getting info from you. I like the weekly news you send out. Very helpful. I’m sure i will have questions later as i grow.

    Reply
  5. Very informative will it be a good idea to get all my equipment and tools needed first so I’m set up and ready to plant indoors?

    Reply
    • Lance,
      That is a good idea. ON the other hand; All you have to be mindful is to not plant seeds before you are set up. So as long as you are set up before starting seeds, it does not matter how you got there. Perhaps you might enjoy our forum at: ilgmforum.com Peace

      Reply
  6. Anyone ever use ozone lamps? Ozone output is quite limited, perhaps a bit stronger than UV lamps. Fans blow towards them and anything reaching them is removed.

    Reply
    • Steven,
      Ozone products can be harmful to Cannabis plants. Be careful what you choose to put into your grow room. 😉

      Reply
  7. We tried twice to buy seeds, both shipments were intercepted by the DEA. We got empty envelopes with letters stating this was a big no-no. What do you do differently to assure I get the seeds should I buy from you? I have gotten a lot of good instructions, have the set up and now I just need the s seeds. My daughter suffered a TBI and she is healing well without all the pharmaceuticals.

    Reply
    • Maci,
      I have no idea if you were ever satisfied on this matter but, I can say that we guarantee all seed shipments and if your seeds get confiscated, we send another order. That is about all we can do. Perhaps you can use a different shipping address and try again. Contact: [email protected] for guarantee satisfaction. 🙂

      Reply
  8. I wanted to return email to Robert Bergman or someone who is real and would give me an accurate email address to use for my questions

    Reply
  9. G,

    Sounds to me like you have way more pots and plants than adequate lighting. I suggest you join the main forum and that will put you in touch with many experienced growers and experts, who are willing to help guide you to a successful grow. Happy growing 🙂

    Reply
  10. Ron,

    Ozone generators are good for cleaning stale air. You do not want an ozone generator in your grow room. you will need to place it in another room.

    I suggest you join our grow support forum, earn the right to post after reading and replying to a few posts, and we will help guide you with information that will allow you to grow successfully. Peace

    Reply
  11. I would like to do a indoor set up like two and half feet area , I would like to know what I need . Currently I have 9 set up 10 inch pots . I have 2ft floresent lights the wall ceiling are reflected . I have fox farm soil , a two speed fans . I’m using auto flowering . I have the spray for the mold as well . I would like to know what else I would need .

    Reply
  12. I’m a first time grower and bought a ozone / uv / and regular filter will that take care of the odor from my plants. Thank ron

    Reply
  13. Well, I have never used MegaMulch. You can grow in any medium if you have grow experience. There is no reason why you cannot be successful using this medium. It may not be optimum but, you might do well. It is a personal choice.

    Perhaps if you joined the ILGM forum, you would find a winder range of answers. We have many knowledgeable growers and mentors on our grow support forum. 🙂

    Reply
  14. Brian ,

    My best advice to you is to do your research and buy the filter you feel would do the best job for you. Since we are not a product testing lab, we cannot truly tell you which unit would be best for you. You have to do the research. WE all use carbon filters and vortex fans; Portable AC units, dehumidifiers; Etc. Etc.

    I will tell you this. I have used a carbon filter that sucks out the warm smelly air and a portable AC unit with an exhaust vent that fits a window. This could work for you, if you have a window to insert the AC unit vent into.

    You get faster replies and a broader base of knowledge, if you join our Support Forum. Peace 🙂

    Reply
  15. I meant to say above…

    The fan is run whenever you need to exhaust heat or humidity out of your grow space, exchanging the hot air with fresh air. And to clarify;
    Fans are CFM cubic feet per minute. So you calculate room size. L’ x W’ x H’, (IN ORDER TO CALCULATE CUBIC FEET of room), and divide the size fan “INTO TOTAL CF of room), to dertermine how many minutes it will run.

    Reply
  16. Poco,

    Let me see if I can explain this. The fan is run whenever you need to exhaust heat or humidity into your grow space, exchanging the hot air with fresh air. This is controlled by a temp/humidity sensor and switch, which turns the unit on when heat or RH gets to high.

    The size of fan is determined by grow room size and how long you want the unit to take exhausting the room completely. Fans are CFM cubic feet per minute. So you calculate room size. L’ x W’ x H’, and divide the size fan you are using to dertermine how many minutes it will run. (There is no how many times per day, it should run when it is supposed to) For example: Joe Homegrower builds a room that is 15′ x 10′ x 10′ = 1500CF So Joe can use a 1500CFM fan to exchange the air in the room in 1 minute. If Joe uses a750CFM fan, the exchange would take 2 minutes If Joe used a smaller 450CFM fan the room would exhaust in approx. 3minutes 20 seconds.

    I hope this clears up the how big, how often questions you had. Peace, lw

    Reply
  17. Grassmaster, I like your post, and for re: We call these growth spurts as cycles. My friend Zandor wrote a great article at thegrowreport years back. Search for it. It has a great breakdown and can help you recognize these cycles.

    Reply
  18. Hi Brian, air fresheners really dont cut it when in full flower, I find the best method is by using an ozone generator , no smell at all, but do not go in your room when the ozone generator is on. hope it helps.cheers Ron

    Reply
  19. Hi
    Im trying to grow one plant in a basement bedroom. Im the only one who uses the basement in my home. Will keep door closed and I am hoping that leaving good odor removing automatic air fresheners will make the odor un noticable

    Any tips to keep my plant smaller so it doesnt produce as much mass?

    Reply
    • Brian,

      You are going to need a carbon filter with a fan to keep the smell down.

      In order to keep plant smaller, yiled lower, and be more tame; You use small posts. 1galoon to 6 liters pots will do for entire grow.

      You would be better off if you joined our support forum and met all the great growers and staff that help people out. Happy Growing! lw

      Reply
  20. Sorry – but your rule for outlets makes no sense to me. Your formula yields 1500m2 air outlet. What exactly do you mean by “air outlet”? Is that the vent size? It would crazy huge = nearly 39m x 39m. Is it the volume of the fan/air movement? If so, the units should be in m3 (cubic meters). If it is fan volume, over what time period – per minute, per hour, per day?

    Reply
  21. nice site, enjoyed roaming around a bit.
    Question: Is grow boost used in addition to “normal” flower nutes? I typically use General Hydroponics (flora-micro, flora-grow, flora bloom)

    Reply
    • Yes, a bloom booster is used in conjunction with your flowering nutes. Get to know the variety of plant that you are growing. Every plant goes through growth spurts during flowering; each one differently. Learn to time the addition of boosters with those growth spurts and remember to slightly back off on the strength of the other nutrients when adding boosters. Keep records, charts and feeding schedules to dial in your plants and maximize your yields. Hope this helps!

      Reply
  22. Would this work just running it buy you see what you think first grow just putting information that I have collected for my own plan
    What I want is a very simple setup up thinking deep water culture 12 or 8 x 5 gallon buckets easy like this https://www.youtube.com/watch?v=ts0iaPRuPjM In 8’x10′ room in groups or 2 or 3 each under 4 X 1000 watt hps Hortilux bulbs just a straight grow
    Is there much advantage to sog or scrog or supercroping what’s your take on those methods would I get more yield from any of these procedures all things being equal in the same amount of space and time?
    Could you guesstimate percentage of increase in yield in same amount of space and time?
    I read an article that yield is defined by the wattage of light 1 pound per 1000 watts if your lucky is this correct?
    Going to be growing White Widow Flowering period: 60 days
    Indoor yield: 500 g/m2 And or Holy Grail Kush Flowering Time: 8-9 weeks. Yield: 500-650 g/m2
    If one has higher or lower gr/m2 does it matter if indoor yield dependent on light?
    I was thinking of cloning for 2 weeks and vegging for 7 = 9 weeks using 4 x 2’ x 4’ fluorescent fixtures = 4 warm bulbs and 4 cool bulbs in the closet bedroom I want to keep the smell in one room
    (2 weeks cloning 7 weeks vegging = 9 weeks and 9 week flowering perpetual cycle)
    Thus eliminating need and care and room and light for a mother plant
    That’s what I’m trying to achieve I will be using 4 x 1000 watt Hortilux bulbs for each 3 x 5 gallon or 2 x 5 gallon DWC buckets want maximum yield with least amount of pails how much harvest could pull from each plant
    If maximum yield defined by wattage of light 1 pound per 1000 watts if you’re lucky is this correct?
    Would it be pointless have 3 x 5 gallons pails at let say .33333 pounds each or 2 x 5 gallon pail at .5 pounds each?
    I’ll never get a pound per light do you think?
    Just want room in case I get lucky do you think a 5 gallon DWC bucket will hold a plant that’s been 2 weeks cloning 7 weeks vegging and 9 week flowering without getting root bound
    Looking for the magic number of pails
    Any criticism or suggestion welcome
    PS: I read an article that said one gram per watt of light that’s 2.20 pounds and another article said 1 pound per 1000 watts
    What is it?
    Thank you in advance for taking the time to answer this
    Have a great day

    Reply
    • Jim, you have many questions in your post. Let me start at the top and I’ll do my best to answer them all. First you open up with the statement, “What I want is a simple setup” followed by, “deep water culture”. For your first time grow, I would not recommend a deep water culture system. If you are interested in hydroponics, I would recommend using a soil-less mixture like ProMix HP. Great product. I have used this with much success; producing over 2 pounds with 4 plants in 10 gallon pots under a single 600 watt hps in a 4×4 grow tent.
      Next you ask about the potential yield difference between sog, scrog and super cropping. Differnt plants respond differently to those methods. It is going to be something you will have to experiment with over the course of several grows. I would start with topping the plant around the 4th to 6th internode and then topping those new shoots after their third internode. This will give you 4 main tops.
      Next I would recommend 4 plants per 1000 watt bulb in a square formation. This will optimize your yields.
      You say you plan on vegging for 7-9 weeks? The lighting you have planned will be insufficient. Your fluorescent setup will only last you for the first few weeks of veg at best. After that I would recommend using a switchable HPS/MH ballast and finish out your veg cycle with 1000 watt metal halide bulbs.
      One final note… Do not let anyone convince you of what your limits are. I have achieved just slightly over 35 ounces under a single 600 watt HPS. The key is the roots. The biggers the roots, the bigger the fruits. You can have big plants in smaller pots, but you cannot expect that root system to produce incredible yields. Think of it like the water system to a city. A small water main will supply every one with water, but the water will flow at each customers house very slowly. A very larger water main will supply each customer with a larger volume of water. Ever notice that your water pressure drops considerably when 2 people in one house try to shower at the same time? If you had bigger pipes in your house, that wouldn’t be an issue. Both showers would operate at full volume. On that same thought, when 2 people try to shower at the same time in one house and the pressure drops considerably, do you think the pressure dropped at your neighbors house? No, because of the large water main connecting the houses. So in closing, bigger roots (the water mains) and bigger plants (pipes in the house) will produce bigger fruits (full volume at each shower head of the house)! Hope this helps!

      Reply

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