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  • Writer's pictureCorey Provencal

Houseplants and Indoor Air Quality, Fact of Fiction?

I should start by saying that I really do love a houseplant and there was a time when my home resembled a jungle.  I also noticed that it was increasingly difficult to maintain so many houseplants properly.  As time went on the number of houseplants was reduced slowly but surely as attrition took over and the little air scrubbers past away from lack of care.  I don’t recall the air quality as being better or worse to be honest but I do know that if I knew then what I know now I would have helped with the attrition.  I will get to that in a minute after we review what the EPA and NASA have to say about this touchy subject.

First the EPA acknowledges that over the past few years there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments.  The EPA also points out that there is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices.

The EPA also makes a sure to remind us that Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic individuals.  I know you already want to jump ahead but let’s see what NASA has to say first.  Be patient.

They report that the foliage of indoor houseplants is capable of removing low levels of pollution; while the roots, assisted by activated carbon filters, removed air pollutants at higher concentrations.  In these tests NASA reports that these filters removed and biologically degraded pollutants before they accumulated.

I am clearly not a NASA scientist so it’s easy to see why I have trouble wrapping my mind around why the activated carbon filter assisted houseplants that remove biological pollutants aren’t listed as activated carbon filter assisted houseplants as opposed to just houseplants.  One would think that activated carbon filter assisted houseplants is truly much more NASA than just plain old houseplants, right?

NASA Simulated Plant Chamber

Regardless of my humble opinion and inability to comprehend the forgotten role of the activated carbon filters and the whole controlled environment issues here is NASA’s list of the top house houseplants that were most effective in removing formaldehyde, benzene, trichloroethylene and carbon monoxide. (I’ll have to get back to you on where to purchase the activated carbon filters)

  1. Bamboo palm

  2. Chinese evergreen

  3. English ivy

  4. Gerbera daisy

  5. Janet Craig” Dracaena

  6. Dracaena “Marginata”

  7. Corn plant

While NASA is making us aware that houseplants are great at filtering out contaminants and adding oxygen back into the air, they seem to leave out the carbon assisted filters role, and that all of their testing was conducted in small controlled environment of a test chamber.  They also neglected to point out that to be effective at the lowest levels of any measured improvement NASA recommends 15 to 18 good-sized houseplants in 6 to 8-inch diameter containers for an average 1,800 square foot house.

John R. Griman (Chief of the Analysis Branch at EPA’s Indoor Air Division) calculates that at the most favorable conditions, it would take 680 plants in a typical house to achieve the same pollutant removal rate NASA reported they achieved in their test chamber.

Many of you may think that I am splitting hairs here but I’d like to share the findings that I’ve documented over the years.  I have conducted my share of indoor air quality assessments in homes and offices and prefer to document the temperature, humidity, particle levels, and any contributors to these areas such as aquariums, pets, those cute little water falls, and yes houseplants.

There are many other contributors to elevated humidity and particle levels but the patterns of elevated humidity and particle levels are far too often found in homes and offices with several houseplants.  I have had several clients tell me that the large number of houseplants in their home or office was to them help improve their indoor air quality.  Then why call me?  I guess the plants just really weren’t helping.

Would you believe that my first recommendation was to remove the houseplants? Well it was.  Would you believe that the air quality as monitored over the next few weeks was drastically improved?  Well it was.  Okay we implemented other means of improving the indoor air quality; I just thought I would file those with NASA’s activated carbon filters.

The truth is that I more often than not find houseplants over watered and often even dead and forgotten.  In many offices houseplants are the responsibility of the custodial service.  I’ve found that these individuals that are hired to maintain the houseplants are rarely trained on the frequency or correct amount of water to provide the plants.

The improvement of indoor air quality is a reduction of airborne and settled particles and the elimination of environments that can support microbial growth and/or areas that may contribute to the airborne and settled particle levels of the indoor environment.  This would include children and pets, I’m kidding.  Children and pets are huge contributors to poor indoor air quality but we would never consider getting rid of them, would we?

Houseplants on the other hand can be a major contributor to poor indoor air quality simply because most of us will never care for our houseplants as a NASA scientists care for their houseplants during experiments.   This I have found to be very consistent in my field assessments.  A few well maintained houseplants are a great asset to any indoor environment but as few as one poorly maintained houseplant can be to sole source of poor indoor air quality.

As for houseplants improving the indoor air quality of an indoor environment such as a home or office, I haven’t found that environment in any of my assessments over the years, not yet anyway.  I believe that far too many houseplants would be necessary to have a measured improvement in indoor air quality.  I also believe that the amount of time it would take to care for that many houseplants sways the pendulum back to the side of source rather than solution.

I just haven’t found that houseplants can improve indoor air quality in a real world indoor environment.  I do find houseplants often poorly maintained and the source of poor indoor air quality in indoor environments.  So I would have to vote fiction on this one.

Enjoy your houseplants but please maintain them properly.

John P. Lapotaire, CIEC

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