Irrigating trees with drip irrigation
Nearly all species of ornamental, specimen and fruit/nut bearing trees, at any stage of growth, will benefit from irrigation applied through a drip or low-volume irrigation system. Considering that trees are the longest living and largest growing living things planted by landscapers, it’s more than a bit ironic that trees are often overlooked when planning and installing a landscape irrigation system.
Maturing and established trees typically have much deeper and more extensive root systems than shrubs and other landscape plants, and young trees are frequently planted in turf or shrub areas, perhaps only receiving irrigation from a sprinkler system more suited and scheduled for shallower rooted plant material.
With drip irrigation systems, the flow rate and spacing of the emitters can be tailored to suit the soil type, so deep watering can be accomplished without run-off, even in heavy, dense clay soils.
When designing a drip system for landscape trees, in addition to normal irrigation system hydraulic calculations, be sure to allow for increased water use per tree over time. Many clients and contractors prefer to install PVC pipe sub surface for the lateral supply lines, and tee off to each tree hole where it terminates with a 1/2” nipple, about 2”above grade.
At this point, ½” drip line (with the appropriate flow rate and spacing)can be connected to the riser with a ½” marlex street ell and adapter. It is then coiled around the dripline of the tree, and ended with a flush cap.
For their first 1-2 years in the ground, younger, newly planted containerized trees need to be irrigated more frequently, on the root ball and out to the drip line. This is best accomplished by coiling the ½” drip line around the top of the root ball, in concentric circles, about 12” apart (space farther apart on clay soils). As the tree matures, the dripline can easily be moved away from the crown, and extended to cover the growing root zone.
Maturing and established trees are best irrigated with ½” emitterline as well; however the tubing should start well away from the crown of the tree. Established trees should be irrigated for longer durations but less frequently than trees that are newly planted, as they have a deeper and more extensive root system.