Many urban soils have poor permeability and infiltration of water (slow drainage). Wet soil that drains slowly can damage roots and make plants susceptible to root decay pathogens. One method to assess infiltration rate of topsoil is to conduct a percolation test. Dig a 12-inch-deep hole the width of a spade. Roughen the bottom and sides to eliminate any glazed, packed soil. Fill the hole to the top with water at least once and soak the surrounding surface so that soil around the hole becomes saturated with water. Wait 24 hours, refill the hole with water, and observe how long it takes for all the water to drain. If any water remains after 24 hours, drainage probably is too slow. An optimal rate of soil drainage for many landscapes is about 1 to 2 inches per hour (roughly 6 to 12 hours are required to drain a 12-inch hole). Credit: Adapted from an illustration by Valerie Winemiller.
