Established plants of Kalanchoe daigremontiana inhibit the growth rate of daughter plantlets that fall within the radius of their root systems. Plantlets which were detached from their parent leaves and planted in fresh substrate increased in stem length at about twice the rate of sister plantlets grown in substrate that had been used previously to grow K. daigremontiana Addition of water extracts of finely cut stems and leaves from older plants caused a retardation of growth similar to that observed in substrate containing Kalanchoe roots Nutrient levels were adequate in all of the above cases. Inhibition is apparently caused by one or more water-soluble, allelopathic substances which are secreted into the substrate through the roots of established plants, and which are present in extracts from stems and leaves of older plants.