Mold Problems - Are House Plants A Cause? Question about sources of mold in homes

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Q. I love houseplants and have many. I have read before that they can cause a problem for mold-sensitive individuals. The article suggested changing from clay pots to plastic pots. Do you recommend this, or suggest getting rid of them entirely? - Debbie, MA
A. Houseplants by themselves do not pose any unique risk of excessive mold exposures.
Many common mold species are described as being phylloplane species, that is, they commonly grow on leaves, particularly dead leaves. On houseplants, it would be dead leaves that would most likely be a source of mold spores that would become airborne. Mold also grows on the surface of soil. As such, soil surfaces in plant pots also have the potential to be a source of airborne mold.
Mold growth on soil surfaces and dead leaves is not likely to be significantly affected by the type of pots that one uses. Switching from plastic to clay pots does not seem to have any scientific basis.
There are very few scientific studies that have attempted to evaluate the potential effect of houseplants on airborne mold spore levels. Early studies approximately two decades ago did not observe any differences in houses with and without houseplants. Most reports are anecdotal, that is, based on personal observations that have not been scientifically evaluated.
On an intuitive basis, one would expect houseplants to be at least a limited source of mold spores. How much of a source would depend on how many are being grown and how well they are being taken care of. Lots of plants with lots of dead leaves would pose a greater potential for airborne mold than a house in which plants are fewer or very well taken care of.
Houseplants can affect airborne mold levels in a house indirectly by causing high-localized relative humidity and damage to materials as a result of excessive and careless plant watering. Water-damaged materials can be a significant source of mold. High relative humidity can result in condensation on wall surfaces and subsequent mold growth.
In my personal and consulting experience, it is these indirect effects that pose the greatest risk of mold exposure to sensitive individuals. Growing many houseplants with careful watering and attention to providing adequate ventilation in high plant density rooms should pose little or no risk to mold-sensitive individuals.