THE FALSE TRUTH On The “12 Best Plants” To Improve Indoor Air Quality

If you have ever been worried that there are too many environmental contaminants in your home or office, there is a simple, safe solution to this problem. How about using plants that clean the air!

The common houseplant has been proven to remove many harmful toxins from the air. Now, you can feel safer in your home or office with a solution that is environmentally-friendly, and beautiful. Who wouldn’t welcome such a healthy fix for unwanted pollutants?

Lately lots of articles extolling the virtues of the “10 Best air cleaning plants according to NASA” have been published online. The key source of this information originates from the National Aeronautics and Space Administration (NASA) study published in 1989 titled – “Interior Landscape Plants for Indoor Air Pollution Abatement.”

What is the FALSE TRUTH?

It’s TRUE, the study did examine the effects of twelve common houseplants on air quality.

What is FALSE, is that NASA never presented these twelve air-filtering plants as the “BEST” choices. They simply reported the results of the plants they used in the study. The study did provide some surprising information on the complex ways in which plants do clean the air

The plants in your office or home are not only decorative, but NASA scientists have found houseplants surprisingly useful in absorbing potentially harmful gases and cleaning the air inside modern buildings.

A sophisticated pollution-absorbing device: the common indoor plants may provide a natural way of helping combat “Sick Building Syndrome”.

Research into the use of biological processes to solve environmental problems, both on Earth and in space has been carried out for many years by Dr. Bill Wolverton, formerly a senior research scientist at NASA’s John C. Stennis Space Center, Bay St. Louis, Miss.

In this article, we will explore the background of this study, explain the results and provide information to help you set up your own, customized plant collection to improve the air quality and general ambiance of your home or office. Read on to learn more.

Why Did NASA and ALCA Perform This Study?

The phenomenon known as sick building syndrome (SBS) came to light in the 1970s. Because of the petroleum shortage, the cost of heating and cooling traditional structures became burdensome to home and business owners. [source]

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For this reason, builders and building designers sought to reduce the cost of heating and cooling by using maximum energy efficiency building techniques. This involved using synthetic super insulation and reducing the exchange of fresh air.

While these two innovations indeed did save energy when heating and cooling buildings, they also resulted in some allergy-related health problems among people working and living in these newly designed buildings.

It soon became apparent that building airtight structures using lots of synthetic materials caused inhabitants to lack the oxygen they needed while experiencing dangerous levels of exposure to a phenomenon known as off-gassing.

This happens when synthetic materials used in building construction and in the creation of modern office equipment and furnishings release volatile organic compounds (VOC). These compounds contribute to poor health in a wide variety of ways.

The earliest recognized symptoms of SBS include:

  • Respiratory congestion
  • Sinus congestion
  • Itching eyes
  • Skin Rashes
  • Drowsiness
  • Headaches

Over the past 30 years, the causes and the definition of SBS have been explored and expanded.

We now recognize that there are also psychological components and instances of increased development of serious diseases, such as certain cancers. These days we can realize a wide variety of factors that contribute to this phenomenon. Among them are:

#1 – Chemical contaminants may be introduced through both outside and inside sources. Faulty ventilation systems can bring in toxins from car exhaust, hazardous manufacturing and other sources. The contaminants introduced in this manner include:

  • Formaldehyde
  • Lead paint
  • Pesticides
  • Asbestos
  • Radon

Simultaneously, indoor sources of contaminants include:

  • Manufactured wood products
  • Combustion byproducts
  • Particulate matter
  • Copy machines
  • Cleaning agents
  • Tobacco smoke
  • Upholstery
  • Adhesives
  • Carpeting

Synthetic fragrances and other ingredients included in cleaning products, personal care products and more also contribute to the problem.

#2 – Biological contamination can also cause SBS symptoms. Contaminants such as:

  • Insect droppings
  • Bird droppings
  • Bacteria
  • Viruses
  • Fungus gnats
  • Pollen
  • Mold
  • Dust

…can also be brought in via faulty ventilation systems. Poor ventilation also fails to carry interior contaminants out of the building.

#3 – Electromagnetic radiation is another serious cause of SBS. This problem is caused by electronic equipment such as computers, TVs, microwaves and also ungrounded electrical wiring.

All of these things are sources of positive ions. Excessive exposure to positive ions can cause suppressed immune function, cancer, anxiety, sleeplessness, emotional distress and more. [source]

#4 – The atmosphere or “feeling” of a building can also cause symptoms of SBS. For example, a very stressful workplace may produce a wide variety of adverse physical symptoms. A workplace that is inappropriately lit can also result in headaches, depression and other health problems.

The NASA Study Did Not Take Modern Day Factors Into Account

SBS when first identified and initially defined in the 1970s, the symptoms were put down entirely to exposure to VOCs off-gassed by synthetic building materials and synthetic materials used in modern furnishings.

In response to this problem, scientists at NASA teamed up with the Associated Landscape Contractors of America (ALCA) to try to find a way to remove three specific volatile organic compounds from the air. These were:

Benzene

Benzene is a solvent found in a wide variety of everyday chemicals and products. Among them are:

  • Petroleum Products
  • Pharmaceuticals
  • Explosives
  • Detergent
  • Rubber
  • Paint
  • Dyes
  • Ink

Exposure to benzene can cause wide-ranging symptoms which include:

  • Dermatitis, inflammation, blistering
  • Psychological disturbance
  • Chromosomal aberrations
  • Irritated skin and eyes
  • Loss of consciousness
  • Bone marrow disease
  • Irregular heartbeat
  • Respiratory illness
  • Loss of appetite
  • Embryotoxicity
  • Kidney damage
  • Blood diseases
  • Liver damage
  • Nervousness
  • Drowsiness
  • Headaches
  • Weakness
  • Paralysis
  • Euphoria
  • Headache
  • Nausea

Trichloroethylene

Trichloroethylene (TCE) is used in adhesives, varnish, lacquer, paint, ink and dry cleaning solutions. According to the Centers for Disease Control (CDC), exposure to TCA can cause cancer of the liver. [source]

Formaldehyde

Formaldehyde is found in almost everything. In building materials, it is a component of foam insulation, particleboard, pressed wood products, floor coverings, carpet backing and more.

You’ll also find formaldehyde in a wide variety of paper products, even those intended for personal care use such as facial tissues, paper towels, and toilet tissue. It is a component of many wrinkle-free and permanent press fabrics. It can be found in cooking fuel, heating fuel, and cigarette smoke.

Exposure to formaldehyde irritates the mucous membranes; causes contact dermatitis; irritates the eyes, nose, throat and upper respiratory tract; causes headaches and (according to the CDC) may cause asthma and throat cancer. [source]

NASA’s Approach To Sick Building Syndrome

When initially identified, poor air quality was believed to be the sole cause of SBS and the associated symptoms. In response, a team of NASA scientists and representatives of the ALCA joined forces to find a solution.

They believed that introducing plants to a closed, artificial environment could help improve air quality by removing three specific substances (benzene, trichloroethylene, and formaldehyde) from the air, and they set about to prove this hypothesis.

The study lasted for two years and focused solely on the use of common house plants as a way of solving indoor air pollution problems.

This study is often cited as proof that growing the specific houseplants used in the study will guarantee clean air in the home. However, a careful reading of the original report indicates that this is not the whole story.

While today many people interpret the results of the study as meaning that the twelve plants the scientists worked with were specially chosen as being the best air cleaning plants.

But, there is nothing to indicate that this is the case.

Information in the final report seems to indicate that the plants used were selected and purchased from local nurseries by the Associated Landscape Contractors of America for use in this study.

No selection criteria were listed, but all the plants chosen are common, easy-to-find, easy-care, low-light houseplants. There is no assertion that these twelve plants are the best or only plants you can use for improving air quality.

It is also important to realize that the scientists did not just study the plants. Their study focused on the effects of the size of the plant’s leaves, their root systems, the soil they were planted in and the microorganisms growing in the soil.

All of these factors are important when considering whether or not and how much indoor house plants affect indoor air quality.

Another factor of this study often skipped over is the use of air circulation and carbon filtration in combination with plants as a way of removing powerful indoor air pollutants such as radon, organic solvents, and cigarette smoke.

The combination of an activated carbon filtration system, powerful aeration, and a houseplant results in very effective air decontamination. The air moves through the carbon filter allowing large amounts of contaminants to be absorbed by the carbon and held for later processing by the plant.


What Are The 12 NASA “Air Cleaning Plants?”

The twelve plants “screened” were:

There is no indication that these plants were in any way deemed to be the “best plants” for air cleaning purposes. They are all low-light plants that can be expected to do well in very contained indoor settings.

Note: In the report, several additional plants were included in the chemical test results. For whatever reason the following plants were NOT listed under the “Materials and Methods” section of the report:

How Were The Plants Tested?

All of these plants were tested in very controlled environments. Each one was kept in a Plexiglas dome with artificial lighting or indirect light and air and humidity controls.

Contaminants were introduced in measured doses, and the contaminant levels were monitored regularly. Parallel testing was done using empty Plexiglas chambers and also chambers containing only pots of soil without plants.

In addition to air quality analysis, the scientists also analyzed the soil in pots both with and without plants. They counted microorganisms in the soil both before and after the introduction of chemicals into the air.

At the end of the first year of the study, the scientists concluded that the soil in the pots also plays a significant role in cleaning the air.

They also found that pots filled with soil but no plants did a fair job of removing chemicals from the air. Those containing plants with green leaves that covered the surface of the soil did not perform as well as the soil alone.

Plants with leaves that grow high on the stem planted in soil covered with pea gravel did not do very well.

The best performers were large-leafed plants with the lower leaves removed and bare soil exposed to the air.

These results brought the researchers to the following conclusion.

The combination of the living microbes in the soil and the respiration of the plants resulted in the highest reduction of toxins and improvement in the ambient air quality.

In addition to this information, the scientists discovered that well-established potted plants that are continuously exposed to chemical contaminants actually perform better as time passes.

This is because standard soil microbes (e.g., Alcaligenes, Flavobacterium, Bacillus, Curtobacterium, Micrococcus, Arthrobacter, Myxococcus, Pseudomonas, Bacillus, and Leuconostoc) adapt and become better able to utilize these contaminants as food with greater exposure.

Good Air Circulation And Carbon Activated Filtration Boosted Results

In addition to the basic tests, the scientists also obtained results from plants equipped with a carbon activated filtration system designed to remove TCA and benzene simultaneously.

New activated carbon is very porous, so when compounds pass through it, they’re taken in and retained by the pores in the material. The idea is that the carbon captures and holds large amounts of contaminants and the plants’ roots and the microbes in the soil eventually extract and process them.

In the course of the experiment, the scientists tested contaminant levels of plants equipped with carbon-activated filtration every 15 minutes. They determined that using this filter in conjunction with plants resulted in complete elimination of trace chemicals inside the Plexiglas dome within 2 hours.

These results were not formally announced as part of the NASA – ALCA study, but understanding the importance of this variation is essential to understanding a plant’s ability to clean the air.

When the results of this study are referenced today, plants alone are often given a great deal of credit for cleaning huge amounts of contaminants from the air very quickly, but this is not the case. The most impressive results of this study were achieved with a combination of carbon activated filtration and plants.

The core takeaway from the results of the NASA study is that low-light requiring plants, in general, are good for air quality in the home.

When used in combination with carbon activated air filters and kept in such a way as to provide good soil exposure, a healthy collection of plants can go far toward helping combat the many and varied problems associated with sick building syndrome.

image of the charcoal filter design

Image from the NASA Study showing the design of the charcoal filtering system.

“A living air cleaner is created by combining activated carbon and a fan with a potted plant. The roots of the plant grow right in the carbon and slowly degrade the chemicals absorbed there,” Wolverton explains.

Adding carbon-activated filtration and air circulation through fans can help filter the polluted indoor air more quickly and efficiently. The scientists at NASA concluded their report on the study by saying that use of carbon activated filtration and fans “should be considered an integral part of any plan using houseplants for solving indoor air pollution problems.”

To use carbon-activated filtration, you may want to experiment with hydroponic gardening.

Carbon activated filtration is an integral part of this kind of gardening, and can easily be incorporated into attractive water features that perform the function of enhancing the environment through sight, sound and production of healthy negative ions. [source]

Incidentally, gentle air movement and the addition of plants and water features are also key elements of Feng Shui, and following these principles is also a popular, attractive and effective way to improve the general ambiance of any setting.

Do The Results Of The NASA Study Reflect Real World Circumstances?

It’s important to understand that these tests were conducted in a very controlled scientific setting. The plants were kept under Plexiglas domes, and contaminants were introduced in measured doses. This is very different from the everyday environment in your home or office.

During the first year of the test very high levels of contaminants were used. During the second year, levels were adjusted to be similar to those found in modern buildings of the time.

It is significant that the test took place nearly 30 years ago, and the synthetic materials in buildings of that time differ somewhat from those we use now.

In the 30 years that have ensued since this test, one would hope that modern synthetic building materials have improved somewhat regarding the amount and types of toxins they give off and the level of off-gassing.

Nonetheless, there are still many concerns about indoor air quality, and as we’ve noted synthetic toxins are not the only contaminants we need to worry about. Biological contaminants, hostile work environment, electromagnetic radiation, poor lighting and many other factors can also contribute to symptoms of SBS.

Can Plants Honestly Solve All These Problems?

It’s easy to see the causes of SBS come from a wide variety of sources. Consequently dealing with SBS is a multi-pronged pursuit. While many current online articles and other information sources confidently tell us that the use of plants is an “absolutely perfect way” to clean indoor air, the real solution is a bit more complicated.

Keeping houseplants can undoubtedly play a significant role in improving oxygen levels and keeping the air clean. But, to avoid SBS related problems, you must also:

  1. Install an efficient heating, ventilation and air cooling system (HVAC) and use clean, high-quality air filters.
  1. Select cleaning products for use in your home with great care to avoid harsh chemicals and strong fragrances that are likely to cause SBS related symptoms.
  1. Pay close attention to your plumbing and your roof. Take care of any leaks promptly to avoid standing water which causes mold and mildew problems.
  1. Prune trees and bushes in such a way that they do not touch the side of your building to prevent having birds, insects, and other pests enter the attic space or contaminate the ventilation system.
  1. Have HVAC Systems inspected and cleaned annually.
  1. Limit exposure to electromagnetic radiation by taking technology breaks and establishing technology-free zones in the workplace and/or in your home.
  1. Make certain electrical wiring in your home and/or place of business is up to code and well-grounded.
  1. Avoid drama in the workplace and at home. Practice smart stress management skills.
  1. Establish stress-free zones by setting up special areas for rest and relaxation that exclude technology and include lots of plants, water features, good air circulation along with peace and quiet.
  1. Let in as much natural or direct sunlight as possible, and supplement with full spectrum lighting for yourself and your home or office plants.

Add Plants To A Whole House Clean Air Plan

When taken as a whole, it’s easy to see that removing contaminants from the air and improving air quality is a complicated process. As we’ve noted, there are many components required to keep the air clean and healthy in a modern building. Plants are certainly one major component in this mix.

You’ll find horticultural businesses specializing in providing plants to office buildings to clean the air, beautify them and improve the quality of life for the inhabitants. One technique often used is the establishment of a rooftop greenhouse through which air for the whole building is filtered.

This kind of setup provides a stress-free, natural getaway where workers can take breaks, relax and rejuvenate. Plants placed throughout the building add a natural touch and make the workplace far more pleasant. However, they cannot be counted on to clean the air on their own.

According to John Girman, former senior science adviser at the EPA, it would actually take nearly 700 large and thriving plants to positively affect air quality in a 1500 square foot home or workplace.

Mr. Girman also points out that “The use of fans to draw air over the soil or mix of large numbers of plants may have the potential to cause microbial problems.” [source]

Most people don’t have the space for vast numbers of plants, and few want to have this sort of humid, jungle-like setting throughout the home or office. Nonetheless, keeping a rooftop greenhouse, a sunroom or dedicated plant room can be a great way to set aside a calm, peaceful area to breathe easy and unwind.

Healthy plants, attractively displayed throughout your home or workplace (especially those kept with carbon-activated filtration and/or as a part of a water feature) will brighten your environment, lift your spirits and help keep the air clean when used in combination with the other components of a good clean air plan.

While more research is needed, Wolverton’s study showed that common indoor landscaping plants can remove certain pollutants from the indoor environment.

We feel that future results will provide an even stronger argument that common indoor landscaping plants can be a very effective part of a system used to provide pollution free homes and workplaces, ” he concludes.

Plants take substances out of the air through the tiny openings in their leaves,” Wolverton said. “But research in our laboratories has determined that plant leaves, roots and soil bacteria are all important in removing trace levels of toxic vapors“.

Combining nature with technology can increase the effectiveness of plants in removing air pollutants,” he said.

Do All Houseplants Work To Clean The Air?

All house plants contribute to some degree to improved air quality in the home. Notice that there are several members of the Dracaena family on the list of chosen plants, and indeed any member of that family would do well in a low-light, indoor setting. Any well-cared-for plants that do well in your environment will help clean the air.

Keep in mind that it’s not just the plant that cleans the air. A plant’s effectiveness at air cleaning is strongly associated with microorganisms in the potting soil or potting mix.

It’s important to remember that maximizing the air exposure of any plant’s roots and soil area is of prime importance. When planting your own houseplants, be sure to use a light, well-aerated or well-drained soil mixture that allows good airflow to promote healthy roots and cleaner air.

Plants that performed best in terms of harboring high numbers of microorganisms in the soil were Mother-in-Law’s Tongue and Peace Lily; however, this does not mean that other plants could not do as well given the right combination of soil and environment.

Proper grooming and culling are also important. Remember that if the plant’s leaves cover the soil, air cleaning qualities are reduced. In the case of Mother-In-Law’s Tongue, you would want to cull out baby plants regularly to prevent having the plant take up the entire surface of the soil.

In the final analysis, all Healthy plants improve air quality, and the plants studied by NASA were not chosen for their special air cleaning abilities. In fact, they seem to have been chosen based on the criteria of availability and suitability as low-light, indoor plants.

Because of this, it is easy to see that your choice of plants for your home should depend more on your preferences and your ability to care for them well, and not so much on the specific results of the NASA study.

You can use plants in your bathroom, throughout your home or office to improve the quality of the air to make it a more pleasant place to live and work – where people feel better, perform better, and enjoy life more.