Mold can begin to grow on wet carpet within 24-48 hours. The length of time it takes for mold to fully develop depends on the type of mold, the temperature and humidity of the environment, and the amount of food or moisture available for the mold to feed on. In general, mold will continue to grow as long as there is a source of moisture present. Once mold begins growing on wet carpet, it can be difficult to remove and may cause permanent damage.