Water Conservation Glossary

ROOT DEPTH
The distance in inches that plant roots extend into the soil. Knowing the average root depth for the plants in each watering zone is important to determine an efficient watering schedule. Shallow roots require more frequent watering than deep roots, which can draw water from a larger soil profile. Average root depths vary with plant type. Trees will have root depths of 24 inches or more. Xeriscape plants will have root depths around 10 inches. Shrubs and perennials will have roots of 8 inches or more. Grass can have deep roots but the average in Utah is around 6 inches. Annuals and bedding plants have the shallowest roots at 4-5 inches. The shallowest roots of the various plants within a watering zone will dictate the watering schedule for that zone. To determine the root depth, do either of the following: 1) Poke a long screwdriver or sharp instrument into some moistened soil. Measure the depth to which the instrument easily penetrates. This is the likely depth to which your roots can easily grow. 2) Use a soil probe to remove a soil core sample. Inspect the core for root hairs. The deepest depth where roots are discovered is the root depth.