Can you use indoor plants for air quality improvement?

Who doesn’t love the way luxuriant plants brighten a home or office? But what about indoor plants for air quality improvement? Is this natural method of air purification effective? Are they any more or less effective than an air purifier for the home?

Citing studies performed by NASA, a number of authors have suggested that houseplants can remove a variety of indoor contaminants such as formaldehyde, carbon monoxide, and benzene. In addition to the NASA studies, there have also been several others through the years by other research groups.

All such studies have been conducted in lab environments where the specific chemicals and their quantities have been tightly controlled. In the real world where pollutants are dynamic, changing in type and quantity continuously over time no evidence has been put forward that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. For this reason the EPA has not taken a stand to endorse houseplants as an effective air cleaning method for homes and offices.

The early NASA studies of indoor plants for air quality improvement were conducted by Dr. B.C. Wolverton, Anne Johnson, and Keith Bounds in 1989. They spent two years testing 19 different common houseplants  for their ability to remove harmful elements such as trichloroethylene, benzene, and formaldehyde from the air. Formaldehyde is commonly found in building materials and many cleaning products. Benzene is found in oils and paints. Trichloroethylene is used in paints, adhesives, inks, and varnishes. Of the 19 plants they studied, 15 were considered to be capable of reducing the studied volatile organic compounds (VOCs).

The NASA list of indoor plants for air quality improvement is as follows:

  1. Philodendron scandens “oxycardium”, heartleaf philodendron
  2. Philodendron domesticum, elephant ear philodendron
  3. Dracaena fragrans “Massangeana”, cornstalk dracaena
  4. Hedera helix, English ivy
  5. Chlorophytum comosum, spider plant
  6. Dracaena deremensis “Janet Craig”, Janet Craig dracaena
  7. Dracaena deremensis “Warneckii”, Warneck dracaena
  8. Ficus benjamina, weeping fig
  9. Epipiremnum aureum, golden pothos
  10. Spathiphyllum “Mauna Loa”, peace lily
  11. Philodendron selloum, selloum philodendron
  12. Aglaonema modestum, Chinese evergreen
  13. Chamaedorea sefritzii, bamboo or reed palm
  14. Sansevieria trifasciata, snake plant
  15. Dracaena marginata, red-edged dracaena

While a lot of publicity has been given to the NASA studies by authors of houseplant books and by the houseplant growing industry, something which is often overlooked is that it was determined the average home would require nearly 680 houseplants to filter the air. Why so many? Because there are a wide variety of pollutants that typically need to be removed and not every individual plant is effective on each pollutant. The original recommendation for formaldehyde removal alone was 70 spider plants for a home of 1800 sq. ft. The researchers revised their assessment afterward to only 15 spider plants but even this is a relatively large number for most homeowners to care for. Add to these plants a comparable number for removal of other VOC’s and the typical home becomes somewhat of a jungle.

Other researchers throughout the world have also sought to determine useful indoor plants for air quality enhancement.

In Study of absorption of VOCs by commonly used indoor plants the researchers selected three indoor plants for air quality decontamination capabilities. These three plants, Howea forsteriana Becc (Kentia Palm), Dracaena deremensis Eng Janet Craig, and Spathiphyllum Petite (Peace Lily), are commonly found throughout the world as houseplants. Each of these was evaluated for the ability to reduce or remove benzene and n-hexane from indoor air.

The plants were found to be capable of removing the individual VOC’s at concentrations equal to 2 and 5 times the maximum occupational exposure levels recommended by the Worksafe Australia Time-weighted average exposure standard. Successful removal initially took from 2–5 days, after which rates increased so that removal was achieved in 24 hours. This accelerated removal ability was determined to be due to the ability of the plant and potting media to create a soil/plant microcosm in which normal soil microflora, possibly triggered by chemical signals from the plant, to induce an enzyme response that increases the capacity of the plants to cope with their polluted environment and thus improve indoor air quality.

These studies, both NASA’s and others, have had mixed results for the use of indoor plants for air quality improvement. While certain specific pollutants may be reduced to a greater or lesser degree by one plant, other pollutants remain unaffected.

It is also important to realize that the potting soils can harbor molds that may become airborne and serve as an allergen. Also, all the water used on the houseplants either evaporates from the pot or transpires through the plants leaves raising humidity in the home. This increased humidity can contribute to increased mold growth elsewhere in the home as well as increased dust mite activity.

Conclusion

The case for using indoor plants for air quality improvement is shaky at best. Natural solutions to the problems brought on by our unnatural environments is currently all the rage in the self help circles. But as desirable as a “back to nature” approach may be, it's important to recognize the limitations of any proposed solution, natural or otherwise. Using indoor plants for air quality purposes is not the most practical way of purifying the air. It requires a vast number of plants to be effective and the plants themselves can contribute to indoor pollution in their own way by increasing humidity and mold growth.

The best solutions to indoor air quality problems remains source control where possible, increasing ventilation to replace polluted air with cleaner outside air, and air purifiers to keep the air indoors healthy and clean.