When plants are stressed (like being cut or dehydrated), they can emit tiny sound vibrations. These sounds are in the ultrasonic range (around 20100 kHz). Humans cannot hear these frequencies (our Clay Soil Garden Plan for Your Front Entry The Old Farmer's Almanac Store How to Care for an Orchid So It Keeps Blooming Extra Large Pot for Trees Eco Friendly Outdoor Planter for Huge Garden Plants and Flowers, Customizable Sizes Available