When watering trees and shrubs, many homeowners place drip emitters close to the trunk or main stem. While this may be appropriate for newly planted trees, established plants benefit from a different approach.
The key is understanding the drip line.
The drip line is the imaginary circle on the ground directly below the outer edge of a plant's canopy. If rain were falling on the leaves and branches, the drip line is roughly where the water would drip from the outermost foliage.
As trees and shrubs grow, many of their water-absorbing roots expand outward toward and beyond the drip line. These young feeder roots are responsible for taking up much of the water and nutrients the plant needs to thrive.
For this reason, drip irrigation emitters should be moved outward as a plant matures. Watering near the drip line encourages roots to spread throughout the soil rather than remaining concentrated near the trunk. A larger root system generally supports healthier growth and better drought tolerance.
Adding emitters is often just as important as moving them. Water from a single emitter spreads only a limited distance through the soil - especially in dry climates and coarse soils. As the drip line expands, additional emitters may be needed to ensure water reaches roots around the entire perimeter.
The same principle applies to fertilization. Nutrients are most effective when delivered where active roots can access them. As trees and shrubs grow, fertilizer delivery points should also move outward to follow the expanding root zone.
A good rule of thumb is to periodically evaluate your irrigation system as your landscape matures. If a tree's canopy has doubled in size since it was planted, its irrigation and fertilization layout may need to grow with it.
Healthy plants don't just need water and nutrients—they need them delivered to the right place.