Indoor plants (or houseplants if you prefer that name) are a nice way to step into the world of gardening, regardless of how much space you have available outside. It’s all fairly manageable in terms of scale and complexity, and you quickly learn the basics of maintaining a plant. You don’t have to worry about the weather, or garden pests to any real degree. Many an avid gardener’s lifelong passion was started with an indoor plant!
More importantly, for those living in high density housing, like flats, or apartments, and that don’t have balconies or outdoor space, indoor plants are the only option if you want your own little personal connection with nature.
Indoor plants are utilised as design features in interior design, and can add interest and a touch of life to an otherwise plain living space. Beyond their aesthetic value, indoor plants have a tremendous health benefit to us, especially in this modern age where we tend to make extensive use of man-made materials, which is not without consequence.
The Health Benefits of Indoor Plants
Here is an extract from NASA-STI (Scientific and Technical Information), and yes, that is the US space agency that builds rockets, satellites, space shuttles and put man on the moon, etc.
NASA describes its STI (scientific and technical information) as “the collected set of facts, analyses, and conclusions resulting from scientific, technical, and related engineering research and development efforts, both basic and applied.” So you can be assured this is hard scientific fact.
What follows is an extract of the article “Plants Clean Air and Water for Indoor Environments” which you can find at:
“Although one of NASA’s goals is to send people to the far reaches of our universe, it is still well known that people need Earth. We understand that humankind’s existence relies on its complex relationship with this planet’s environment—in particular, the regenerative qualities of Earth’s ecosystems.
At a test center in Florida, he was heading a facility that discovered that swamp plants were actually eliminating Agent Orange…
In the late 1960s, B.C. “Bill” Wolverton was an environmental scientist working with the U.S. military to clean up the environmental messes left by biological warfare centers. At a test center in Florida, he was heading a facility that discovered that swamp plants were actually eliminating Agent Orange, which had entered the local waters through government testing near Eglin Air Force Base. After this success, he wanted to continue this line of research and moved to what was at the time called the Mississippi Test Facility, but is now known as NASA’s Stennis Space Center.
He was funded by the Space Agency to research the environment’s natural abilities to clean itself as part of what is now Stennis’ Environmental Assurance Program. The goals were to clean the Center of chemicals left behind through wastes and to supply information to NASA engineers about closed-environment “eco” support that may prove helpful in designing sustainable living environments for long-term habitation of space. A tertiary goal was to provide usable technologies to NASA’s Technology Utilization Program, essentially making the research available to the American public.
The first step for Wolverton’s research was to continue the remediation work he had started with the military. He was tasked with using plants to clean waste water at the NASA Center. To this day, Wolverton’s design, which replaces a traditional septic system with water hyacinths, is still in use. His research then turned to using plants to improve air quality.
…NASA scientists identified 107 volatile organic compounds (VOCs) in the air inside the Skylab space station. Synthetic materials … used to construct Skylab, give off low levels of chemicals… such as formaldehyde, benzene, and trichloroethylene, all known irritants and potential carcinogens.
In 1973, NASA scientists identified 107 volatile organic compounds (VOCs) in the air inside the Skylab space station. Synthetic materials, like those used to construct Skylab, give off low levels of chemicals. This effect, known as off-gassing, spreads the VOCs, such as formaldehyde, benzene, and trichloroethylene, all known irritants and potential carcinogens. When these chemicals are trapped without circulation, as was the case with the Skylab, the inhabitants may become ill, as the air they breathe is not given the natural scrubbing by Earth’s complex ecosystem.
Around the same time that Wolverton was conducting his research into VOCs, the United States found itself in an energy crisis. In response, builders began making houses and offices more energy efficient. One of the best ways to do this was to make the buildings as airtight as possible. While keeping temperature-controlled air in place, this approach reduced circulation. Combined with the modern use of synthetic materials, this contributed to what became known as Sick Building Syndrome, where toxins found in synthetic materials become concentrated inside sealed buildings, making people feel sick.
“If man is to move into closed environments, on Earth or in space, he must take along nature’s life support system.” Plants.
The solution Wolverton sought was not to make indoor environments less energy efficient or to move away from the convenience of synthetic materials; rather, the plan was to find a solution that restores personal environments. The answer, according to a NASA report later published by Wolverton in 1989, is that “If man is to move into closed environments, on Earth or in space, he must take along nature’s life support system.” Plants.
Before the houseplants were added, … anyone entering the newly constructed facility would experience burning eyes and respiratory difficulties… Once the plants were introduced… the symptoms disappeared.
One of the NASA experiments testing this solution was the BioHome, an early experiment in what the Agency called “closed ecological life support systems.” The BioHome, a tightly sealed building constructed entirely of synthetic materials, was designed as suitable for one person to live in, with a great deal of the interior occupied by houseplants. Before the houseplants were added, though, anyone entering the newly constructed facility would experience burning eyes and respiratory difficulties, two of the most common symptoms of Sick Building Syndrome. Once the plants were introduced to the environment, analysis of the air quality indicated that most of the VOCs had been removed, and the symptoms disappeared.
After serving over 30 years as a government scientist, Wolverton retired from civil service but continued his work in air and water quality by founding Wolverton Environmental Services Inc. The company, based just down the road from Stennis in Picayune, Mississippi, is an environmental consulting firm that gives customers access to Wolverton’s decades of cutting-edge bioremediation research.
Wolverton published his findings about using plants to improve indoor air quality in dozens of technical papers while with the Space Agency and as a simple consumer-friendly book, “How to Grow Fresh Air: 50 Houseplants That Purify Your Home or Office.” In it, he explains, in easy-to-understand terms, how plants emit water vapor that creates a pumping action to pull contaminated air down around a plant’s roots, where it is then converted into food for the plant. He then goes on to explain which plants and varieties remove the most toxins, as well as to rate each plant for the level of maintenance it requires. The book has now been translated into 12 languages and has been on the shelves of bookstores for nearly 10 years. Wolverton has also published a companion book, “Growing Clean Water: Nature’s Solution to Water Pollution,” which explains how plants can clean waste water…”
So yes, Sick Building Syndrome is a fact, synthetic man-made materials do release toxic and dangerous volatile organic compounds, many of them carcinogenic (cancer causing) into the air inside buildings, and indoor plants do remove them from the air.
Obviously there are others who disagree with the findings of NASA but consider this point. NASA’s agenda is purely scientific, about maintaining conditions that support life up in outer space. Back down here on the ground, this information runs counter to the financial interests of those manufacturing man made building materials, paints, plastics and other synthetics, fuels, solvents, pesticides, cleaning compounds, detergents and almost everything else coming out of the chemical industry!
Top 20 Clean Air Plants
Research has shown that certain indoor plants are better at removing specific chemicals than others.
The following table is from the book “Eco Friendly House Plants” by B C Wolverton (Publisher: Weidenfeld & Nicolson, United Kingdom, 1996)
It lists the 20 plants that were rated the highest for removal of chemicals from the air out of the fifty plants tested.
Full sun = min. 5 hrs of sun
|Semi-sun||Easy to grow. Requires high humidity|
|Semi-sun||Easy to grow|
|Semi-sun||Easy to grow|
|Semi-shade||Easy to grow|
|Dracaena ‘Janet Craig’
(Dracaena deremensis ‘Janet Craig’)
|Easy to grow|
|Requires high humidity.
Prone to spider mite.
|Dwarf Date Palm
(Ficus macleilandii ‘Alii’)
|Full sun||Easier to grow than F. Benjamina|
(Nephrolepis exaltata ‘Bostoniensis’)
|Requires humidity and good light|
|Peace Lily (Spathiphyllum sp.)||
|Easy to grow|
(Dracaena fragrans ‘Massangeana’)
|Semi-shade||Very easy to grow|
|Full sun||Easy to grow|
(Dieffenbachia ‘Exotica Compacta’)
|Very easy to grow.
|Full sun||Requires draught-free environment|
|Full sun||Bulb poisonous when eaten|
(Chlorophytum comosum ‘Vittatum’)
|Easy to grow|
The Number of Indoor Plants to Use
NASA’s research recommends 15 to 18 good sized plants in 6-8 inch (15-20cm) wide pots to improve the quality of the air in a 1,800 square-foot (167 square-metre) house.
If you need to scale this down to a smaller space, such as a room or office, the recommendation is a minimum of two plants per 100 square feet of floor space in a building with 8- to 10-foot ceilings.
The rates at which plants clean the air will vary depending on the size of the plant (the effectiveness improves as the plant grows), the temperature of the air and the amount of pollution present.
The area of space surrounding a person, about 0.17 to 0.23 cubic metres (6-8 cubic feet) of it in fact, is termed the personal breathing zone. This is usually areas where an individual remains for several hours working, watching TV or asleep. Plants placed within this zone can add humidity, remove bioeffluents and chemical toxins and suppress airborne microbes.
Plant-filled rooms contained 50 to 60% fewer airborne moulds and bacteria than plant-less rooms.
Volatile Organic Compounds (VOCs) and their Sources
Volatile Organic Compounds (VOCs) area a group of chemicals that contain organic carbon, and readily evaporate – changing from liquids to gases when exposed to air.
Should you be worried about these pollutants? Are they really a concern?
Most definitely! In case you have any doubts, and haven’t realised that all technological progress comes at a price, then read on.
I’ve included an extract from the National Library of Medicine’s article “Volatile Organic Compounds“
How can volatile organic compounds affect my health?
The health effects of volatile organic compounds can vary greatly according to the compound, which can range from being highly toxic to having no known health effects. The health effects of volatile organic compounds will depend on nature of the volatile organic compound, the level of exposure, and length of exposure.
benzene is “known to be a human carcinogen”; formaldehyde and percholroethylene are “reasonably anticipated to be carcinogens.”
According to the Eleventh Report on Carcinogens published by the National Toxicology Program, benzene is “known to be a human carcinogen”; formaldehyde and percholroethylene are “reasonably anticipated to be carcinogens.” People at the highest risk of long-term exposure to these three volatile organic compounds are industrial workers who have prolonged exposure to the compounds in the workplace; cigarette smokers; and people who have prolonged exposure to emissions from heavy motor vehicle traffic.
Long-term exposure to volatile organic compounds can cause damage to the liver, kidneys and central nervous system. Short-term exposure to volatile organic compounds can cause eye and respiratory tract irritation, headaches, dizziness, visual disorders, fatigue, loss of coordination, allergic skin reactions, nausea, and memory impairment.
That should clear up any doubts about the nature of these substances.
You may be wondering where how these chemicals get into your indoor living space in the first place.
From the Minnesota Department of Health’s article “Volatile Organic Compounds (VOCs) in Your Home“, I’ve reproduced portions of the article for the purpose of reference, as it provides further information on VOC sources.
Volatile Organic Compounds (VOCs) are a large group of carbon-based chemicals that easily evaporate at room temperature. While most people can smell high levels of some VOCs, other VOCs have no odor. Odor does not indicate the level of risk from inhalation of this group of chemicals. There are thousands of different VOCs produced and used in our daily lives. Some common examples include:
- Ethylene glycol
- Methylene chloride
Where do VOCs come from?
Many products we have in our homes release or “off-gas” VOCs. Some examples of sources of VOCs are:
- Carpets and adhesives
- Composite wood products
- Sealing caulks
- Upholstery fabrics
- Vinyl Floors
Home and Personal Care Products
- Air fresheners
- Air cleaners that produce ozone
- Cleaning and disinfecting chemicals
- Fuel oil, gasoline
- Moth balls
- Vehicle exhaust running a car in an attached garage
- Non-electric space heaters
- Stored paints and chemicals
- Wood burning stoves
Studies have shown that the level of VOCs indoors is generally two to five times higher than the level of VOC’s outdoors. VOC concentrations in indoor air depend on many factors, including the:
Amount of VOCs in a product;
- Rate at which the VOCs are released;
- Volume of the air in the room/building;
- Ventilation rate or the area; and
- Outdoor concentrations of VOCs.
What are the health effects of VOC exposure?
The risk of health effects from inhaling any chemical depends on how much is in the air, how long and how often a person breathes it in. Scientists look at short-term (acute) exposures as hours to days or long-term (chronic) exposures as years to even lifetime.
Breathing low levels of VOCs for long periods of time may increase some people’s risk of health problems. Several studies suggest that exposure to VOCs may make symptoms worse in people who have asthma or are particularly sensitive to chemicals. These are much different exposures than occupational exposures to VOCs.
VOCs refer to a group of chemicals. Each chemical has its own toxicity and potential for causing different health effects. Common symptoms of exposure to VOCs include:
Short-Term (Acute) to high levels of VOCs
- Eye, nose and throat irritation
- Nausea / Vomiting
- Worsening of asthma symptoms
- Long-Term (Chronic) to high levels of VOCs
Increased risk of:
- Liver damage
- Kidney damage
- Central Nervous System damage
What levels of VOCs is safe?
The best health protection measure is to limit your exposure to products and materials that contain VOCs when possible. If you think you may be having health problems caused by VOCs, try reducing levels in your home. If symptoms persist, consult with your doctor to rule out ore serious health conditions that may have similar symptoms.
How do I reduce the levels of VOCs in my home?
The most effective action is to remove the product that gives off VOCs. Most products containing VOCs will off-gas within a short period of time, although some will continue to give off VOCs for a longer period of time.
Some steps you can take to reduce your exposure to VOC in the home are:
- Source control: Remove or reduce the number of products in your home that give off VOCs. Only purchase amounts of chemicals that you know you will use and carefully follow directions on product labels. Remove unused chemicals from the home because stored chemicals in closed containers can sometimes “leak” and release VOCs into indoor air. Check with city or county for household hazardous waste collection sites. For new items consider purchasing:
- floor models that have been allowed to off-gas in the store
- solid wood items with low emitting finishes
- new products that contain low or no VOCs (environmentally preferable products)
- As a last resort, airtight sealers have been used to minimize VOC emissions. Check with vendors of composite wood products to choose a non-toxic sealant to reduce exposure to VOCs.
2. Ventilation and climate control can be used to reduce exposure to VOCs.
- Increase ventilation by opening doors and windows, use fans, maximize air brought in from outside;
- Keep both the temperature and relative humidity as low as possible or comfortable. Chemicals will off-gas more under warmer conditions with high humidity; and
- If you have a choice, perform renovations when home is unoccupied or during seasons that will allow for additional ventilation.
- In summary, the most effective way to limit VOCs indoors is to limit the potential sources of VOCs. Increasing the amount of outdoor “fresh air” into a space can also dilute and reduce VOC levels.
I’m hoping at this point that I haven’t terrified you into filling every square inch of your home completely with plants! The point, which I hope I’ve sufficiently illustrated, with factual evidence from credible sources, is that VOCs are very toxic substances present in our indoor living spaces that can effectively be reduced/removed with indoor plants.
How Plants Clean the Air
Most indoor plants have very high rates of photosynthesis which allow them to grow in very dim light, because they typically grow under the shade of the canopy of tropical or subtropical forests. This attribute also allows them to grow indoors.
The plant’s leaves, roots, soil and micro-organisms work together in a symbiotic relationship to removal chemical pollutants:
Air pollutants are are removed from the air by being absorbed through microscopic pores in plant’s leaves called stomata. They are moved, by a process called translocation, which moves sugars and other substances through the plant, to the root zone, where they are broken down by soil microbes. Some chemicals, are, however, broken down by the plant’s own biological processes without involving the action of soil microbes.
Soil microbes break down the pollutants into substances that can be used as food by the microbes and the plant.
Soil microbes break down the pollutants into substances that can be used as food by the microbes and the plant. Many different types of micro-organisms live in the soil, and one of the many things that they do is to make nutrients available to plants and to detoxifying the soil.
Soil microbes adapt readily to their surroundings, as they have the ability to mutate in response to changes in their environment. The longer they are exposed to toxic substances, the better they become at breaking them down, so, the longer we keep our houseplants, the better they will be in their ability to clean the air.
While most plants open the pores in their leaves (stomata) during the day for photosynthesis, and therefore absorb air pollutants during that time, some plants, including most cacti, succulents, orchids and bromeliads, act in the opposite way, opening their stomata at night, and therefore absorbing air pollutants at night. So, with the right selection of indoor plants, you can continuously purify the air, day and night!
And One Final Note…
Since I’ve mentioned references to the Top 50 plants recommended by Dr. B.C. Wolverton from “How to Grow Fresh Air: 50 Houseplants that Purify your Home or Office” throughout this article, I thought it best to list the 50 plants to satisfy your curiosity!
Please note, many other plants can also remove chemical air pollutants too, and this is just the list of the ones tested and included in Dr. Wolverton’s book.
|Areca Palm||Chrysalidocarpus lutescens|
|Lady Palm||Rhapis excelsa|
|Bamboo Palm||Chmaedorea seifrizii|
|Rubber Plant||Ficus robusta|
|Dracaena “Janet Craig”||Dracaena deremensis “Janet Craig”|
|English Ivy||Hedera helix|
|Dwarf Date Palm||Phoenix roebelenii|
|Ficus Alii||Ficus macleilandii “Alii”|
|Boston Fern||Nephrolepis exaltata “Bostoniensis”|
|Peace Lily||Spathiphyllum sp.|
|Corn Plant||Dracaena fragrans “Massangeana”|
|Golden Pothos||Epipremnum aureum|
|Kimberley Queen||Nephrolepis obliterata|
|Florist’s Mum||Chrysanthemum morifolium|
|Gerbera Daisy||Gerbera jamesonii|
|Dracaena “Warneckei”||Dracaena deremensis “Warneckei”|
|Dragon Tree||Dracaena marginata|
|Red Emerald Philodendron||Philodendron erubescens|
|Dumb Cane||Dieffenbachia “Exotica Compacta”|
|Parlor Palm||Chamaedorea elegans|
|Weeping Fig||Ficus benjamina|
|Wax Begonia||Begonia semperflorens|
|Lacy Tree Philodendron||Philodendron selloum|
|Heart-Leaf Philodendron||Philodendron oxycardium|
|Snake Plant||Sansevieria trifasciata|
|Dumb Cane||Dieffenbachia Camilla|
|Elephant Ear Philodendron||Philodendron domesticum or Philodendron tuxla|
|Norfolk Island Pine||Araucaria heterophylla|
|King of Hearts||Homalomena wallisii|
|Prayer Plant||Maranta leuconeura “Kerchoveana”|
|Dwarf Banana||Musa cavendishii|
|Christmas and Easter Cactus||Schlumbergera bridgesii, Schlumbergera rhipsalidopsis|
|Oakleaf Ivy||Cissus rhombifolia “Ellen Danika”|
|Lily Turf||Liriope spicata|
|Dendrobium Orchid||Dendrobium sp.|
|Spider Plant||Chlorophytum comosum “Vittatum”|
|Chinese Evergreen||Aglaonema crispum “Silver Queen”|
|Croton||Codiaeum variegatum pictum|
|Dwarf Azalea||Rhododendron simsii “Compacta”|
|Peacock Plant||Calathea makoyana|
|Aloe Vera||Aloe barbadensis|
|Urn Plant||Aechmea fasciata|
|Moth Orchid||Phalenopsis sp.|