Depending on the size and type of the plant, you will need to water to different depths and widths. A large tree needs more water than a small groundcover, because it has a larger root zone-the area in which the plant's feeder roots are concentrated. Your plants will be healthiest if you completely wet the root zone each time you water.
After plants are established, most water absorbing roots are located near the drip irrigation line which is beneath the outer edge of the plant's canopy, not close to the trunk or stem. Concentrate your emitters along the dripline of each plant. The water will spread down and horizontally as it soaks into the soil.
The 1-2-3 Rule is an easy way to remember how deep to water:
- Water small plants such as annuals to a depth of 1 foot.
- Water medium plants such as shrubs to a depth of 2 feet.
- Water large plants such as trees to a depth of 3 feet.
A good way to test how deep you have watered is to use a soil probe such as a sharpened piece of rebar or a very long screwdriver. About an hour after watering, push the probe into the soil. It will slide easily through wet soil but will be difficult or impossible to push through dry soil. Water your plants and lawn until you can easily slide the probe to the recommended depth.
The term "established" refers to the point at which a newly planted tree, shrub, accent, or ground cover begins to produce new growth. New growth appears as fresh foliage or new stems. Typically, the root system of a shrub will be well established after one year. A tree will be well established after three years. New plantings need to be watered more frequently than established plants.
Grass or turf should be watered to a depth of 10 inches. Apply about .75" (¾ inch) of water each time you irrigate your lawn to wet the root zone.