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

By Eric Hopper
Published: October 17, 2019 | Last updated: April 21, 2021 05:23:30
Key Takeaways

Air purification is one of the most overlooked variables of an indoor garden because most airborne pathogens are invisible, but ignoring this factor could invite all sorts of problems into the growroom. Eric Hopper explains why "out of sight, out of mind" holds true.

Source: Antonio Guillem/

Indoor horticulturists spend a lot of time and money trying to provide ideal environmental conditions for their gardens. Using various devices and equipment, growers can create artificial light energy, irrigation or hydroponic systems, and atmospheric conditions that meet or exceed the needs of their plants.


Serious horticulturists experiment and fine-tune each variable that affect a growroom’s performance until the optimal parameters are found. One variable that an increasing number of gardeners are paying closer attention to is the air quality within the garden. Aside from temperature and humidity, other elements in the air that can impact a high-performance indoor garden.

Many of the pathogens that enter an indoor garden do so through the air. Without proper air purification, an indoor horticulturist could be inviting potential problems into the garden.


5 Things That Are Floating in Your Grow Room

Like it or not, there are at least one of these things in the air of your grow room right now:

1. Molds and Fungi Spores

Most of the problematic molds and fungi found in an indoor garden are transmitted through the air—powdery mildew, black spot and botrytis are just three examples. Given the right conditions, these opportunistic fungi quickly wreak havoc on otherwise healthy plants and can decimate an entire crop in a short period of time.

The spores are invisible to the naked eye and are often overlooked by novice growers. Once a crop is infected, it can take serious work to entirely eradicate the fungi. Eliminating airborne fungi with an air purification device is by far the best defense against infection.


Read: Tips for Preventing Mold Growth in the Grow Room

2. Bacteria

Although not as common as molds and fungi, airborne bacteria can also cause problems for certain indoor crops. Bacterial infections can cause a variety of symptoms, including blights, cankers, galls, leaf spots, overgrowth, specks, scabs or wilts. They are also usually hard to identify and are often misdiagnosed as a nutrient deficiency.


Like many fungi spores, novice gardeners often overlook bacteria as a potential threat because they are invisible to the naked eye. In many cases, growers never attribute the problem they are experiencing to airborne bacteria and never properly protect their gardens from such a threat. Treating a bacterial infection in plants is rather difficult. As with pathogenic fungi, prevention is the most effective defense.

3. Pollen

For some indoor gardeners, unwanted pollen in the air can cause problems. Cross-contamination of species can ruin an entire crop, especially if the grower is attempting to perform controlled breeding. Many fast-growing annuals, such as peppers, can be cross-pollinated, which creates unstable offspring.

In fact, a hot pepper could pollinate a sweet pepper and the seeds can produce either hot or sweet peppers with no way of telling which will be which. For seed producers, it is imperative to keep similar species’ pollen separate from each other.

4. Pest Insects

Some of the worst pest insects enter an indoor garden through the air. Spider mites create a small strand of webbing that acts much like a parachute, allowing them to relocate via the wind. Unsuspecting gardeners can suck these tiny pest insects into their growrooms through their ventilation systems.

An inexpensive fix for this type of problem is a large particulate screen on the room’s intake vent. Growers on a budget can stretch a nylon sock over the intake ventilation port.

Read: Beginner's Guide to Beneficial Insects

5. VOCs and Odors

Volatile organic compounds, or VOCs, are chemical compounds (gases) found in the air. Although most VOCs affects the grower more than the plants themselves, they are still something any indoor horticulturist should consider when addressing the air purification of a garden. Indoor gardens can produce a variety of odors, from fertilizer smells to plant odors. These are all types of VOCs.

Although most odors are more of a nuisance than a detriment, some, like the ones left behind by chemical insecticides or fungicides, can be dangerous. Air purification devices that eliminate or reduce odors can be an effective way to destroy VOCs found in and around an indoor garden.

4 Types of Air Purification Devices

Once a horticulturist understands the potential dangers lurking in the air, he can take the precautions necessary to reduce or eliminate those threats. Indoor gardeners who implement advanced air purification techniques can decrease pathogens, pollens and VOCs found in the air and create a healthier environment. There are many different air purification devices available and each has its own advantages and disadvantages. By taking a closer look at some of these devices, a grower can decide which is best for their garden.

1. Carbon Filters

Carbon filters are one of the most commonly used air purification devices by indoor horticulturists. Carbon filters use activated carbon, which is carbon treated with oxygen. As the oxygen opens up millions of tiny pores in the carbon, this allows a large surface area to attract and neutralize VOCs, along with some chemicals and fumes. A chemical reaction occurs in the carbon that, in turn, causes the carbon to absorb the airborne material.

It's in this way that carbon filters are effective at reducing VOCs in a garden.They can be used to recirculate the air within a garden space to help filter the air or, in many cases, are used as both intake and exhaust filters for the ventilation system.

But carbon filters do have a few limitations. First, the larger the area that needs to be treated, the more activated carbon is required.

This makes carbon filters heavy and, in many cases, bulky. For growers with a limited space, this is a serious disadvantage. One solution is to hang carbon filters above the plants so that the filter will not take up any precious floor space.

Another limitation of carbon filters is their longevity. Like other filters, once the activated carbon has absorbed its maximum capacity of contaminants, it is no longer effective. This means they must be replaced regularly. For most indoor growers, replacement occurs annually. Although carbon filters are extremely effective at reducing VOCs, they are not always effective at filtering pollen, fungal spores or bacteria.

Read: Understanding Air Purification and Activated Carbon Filters

2. HEPA Filters

High-Efficiency Particulate Air (HEPA) filters are paper-like filters that remove particles from the air down to 0.3 microns in size. Many mold spores are in the 1 to 20 micron size range, making HEPA filters a good choice for trapping mold spores. HEPA filters will also filter larger particulates out of the air, including insects.

These filters are popular as an intake filter for many indoor horticulturists. Like carbon filters, HEPA filters have some drawbacks. First, they are not good at removing VOCs. Growers wishing to remove VOCs along with the fungi and mold spores will have to use a carbon filter as well.

HEPA filters add significant resistance, so the required CFM (cubic feet per minute) of the intake fan within a ventilation system will increase when using one.

The biggest drawback is with regards to what happens to the fungal spores. Although some HEPA filters include an antimicrobial coating, they can trap a large number of viable spores. These have the potential to be released when the grower removes the filter, setting off an invisible fungi bomb.

3. Ozone Generators

One of the most effective ways a gardener can destroy molds, bacteria, and VOCs is with an ozone generator. Ozone oxidizes any molds, bacteria, and VOCs that it comes in contact with. Unfortunately, ozone levels that are high enough to continually purify the air of an indoor garden are also high enough to damage the grower’s lungs.

High concentrations of ozone within an indoor garden can also be detrimental to the plants themselves because it oxidizes essential oils on the plants, causing the plants to lose quality and vitality.

Read more: Ozone - An Indoor Garden Super Tool

4. Photocatalytic Air Purification Systems

One of the best devices for air purification is a photocatalytic air purifier. These purifiers use a specialized UV lamp to stimulate a chemical reaction from a catalyst which then produces powerful oxidizers.

Not all photocatalytic air purifiers are created equal. Some contain UV lamps that produce ozone and are really nothing more than hyped-up ozone generators.

The ones perfect for indoor horticulture create powerful oxidizers that never leave the reaction chamber. These devices have the ability to recirculate the air within the garden and remove mold and fungi spores, bacteria, viruses, pollen, and VOCs without producing any detectable ozone.

Unlike filtration devices, a photocatalytic air purification system doesn’t trap these pathogens. Instead, it destroys them on contact. The good ones combine all the advantages of a carbon filter, HEPA filter and ozone generator. In other words, photocatalytic air purification devices are the bee’s knees when it comes to air purification of an indoor garden.

The main drawback of these devices is the initial cost. A true photocatalytic air purification system—one that does not produce ozone and oxidizes on contact—is not cheap. But they're well worth it in the long run; these devices will pay for themselves again and again and will give the grower years of powerful prevention against a score of problems.

The Power of Prevention

Implementing one or a combination of air purification devices is a good way to protect your garden against airborne pathogens.

Every garden is different and the air purification needs of each room will vary. Experienced growers understand the power of prevention and are more than willing to implement such devices if they will prevent any potentially devastating problems in the future.

As previously mentioned, air purification is one of the most overlooked variables of an indoor garden because most of the airborne pathogens are invisible.

In this case, the old saying holds true: out of sight, out of mind.

As we learn more about plant physiology and the effects of airborne pathogens, more growers are becoming mindful of the potential dangers that can lurk in the air and will do everything in their power to stop them.

Read next: Removing Pollutants from Indoor Air


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Written by Eric Hopper | Writer, Consultant, Product Tester

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Eric Hopper’s past experiences within the indoor gardening industry include being a hydroponic retail store manager and owner. Currently, he works as a writer, consultant and product tester for various indoor horticulture companies. His inquisitive nature keeps him busy seeking new technologies and methods that could help maximize a garden’s performance.

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