Having healthy plants indoors is a wonderful thing. Communing with nature and other life forms tends to have a positive impact on the human psyche. Plants produce oxygen and help to eliminate carbon dioxide that humans and other animals exhale. There are also studies that suggest plants help to eliminate mold spores and bacteria. All of the above statements express sentiments with which I substantially would agree. Having lots of plants indoors, however is a double-edged sword.
There is growing evidence that plants do have a positive impact on the quality of the indoor air, so the basic belief or instinctual reaction is valid. It has been demonstrated that plants, and there are specific plants that have been shown to perform better than others, can help to control some airborne microorganisms. Plants can also remove substantial quantities of volatile organic compounds (VOC), including formaldehyde, from the air. Research shows that photosynthetic action of the leaves plus the activity of some soil microorganisms both contribute to this purifying action. English Ivy, Asparagus Fern, and Purple Heart Plant are some of the most effective toxin removing plants.
Indoor plants, however, also have their negative side that often more than counteracts their enhancement of indoor air quality. One of the first items I check when conducting an indoor air quality investigation are plants, which are sometimes more of a contaminant source than they are a benefit. In order to produce sufficient oxygen or to eliminate enough carbon dioxide to have a significant impact on the quality of the indoor air, it would be necessary to have a virtual jungle of plants, but the toxin reduction can still be valuable with fewer plants. The overall effect of indoor plants tends to be quite beneficial in terms of helping to purify the air if they are properly maintained. Plants become a contaminant source due primarily to improper care. Over-watering is not only destructive to the health of the plant, but can result in substantial growth of molds and bacteria. Using wadded up newspaper or paper bags to center a potted plant inside a decorative pot opens up the possibility of mold growth on that paper when it becomes wet when watering the plant. Mold growth on paper or other materials containing high levels of cellulose is often a potentially toxic mold, such as Stachybotrys. This is the notorious villain in most news reports that deal with mold contamination. I should state at this point, that health effects due to inhaling mold toxins is a controversial topic and has not been clinically established.
Sphagnum moss is a high cellulose containing decorative material often placed on top of the plant's soil in part to help retain moisture. Placing this material on top of wet soil, thereby causing the moss to become wet, can produce mold growth on this material as well. Again we have mold growth on a high cellulose containing material, so the possibility for growth of potentially toxic molds.
Using a professional plant service to maintain the plants is by no means a guarantee that the plants conform to proper indoor air quality standards. I have found that even though the plants appear to be healthy and beautiful, they often have the problems presented above. This can result in mold growth potentially contaminating the air in the vicinity of the plant and beyond. To ensure that plants are indeed a benefit to the quality of the indoor air, properly maintain them. There must be certain restrictions. Those restrictions must include prohibiting the use of any paper product inside the decorative pot either for centering or any other purpose. Sphagnum moss, if it is to be used, must be regularly replaced in the event that it becomes wet and moldy. It is not as susceptible to mold growth as paper, but it has been found to be a source of mold contamination numerous times in my experience.
Senior Indoor Air Quality Investigator