Gravity plates, also known as petri dish tests, offer a simple way to begin exploring indoor air quality. Each dish contains a layer of nutrient-rich gel that allows airborne mold spores to grow into visible colonies. When you open the plate and leave it out for a period of time—typically one hour—spores settle onto the gel naturally. Once sealed and shipped to a lab, the plate is incubated, and the lab reports on both the quantity and type of mold that grows.

This form of testing is easy to use and relatively inexpensive. It doesn’t require pumps or sampling equipment, which makes it ideal for homeowners, renters, or individuals with limited access to professional tools. While gravity plates don’t provide all the answers, they’re often a good starting point when mold is suspected but not visible.