Watering Trees in Turf
Watering Mature Trees
Provide sufficient water to keep trees healthy, while following drought regulations and not wasting water.
Reduce tree losses, as trees take many years to mature, and dead trees are dangerous and expensive to remove.
1. Change irrigation hardware
Change the heads to low volume (MP rotors or similar to allow for deeper watering. (Turf spray heads usually deliver 0.5 to 1 gallons per minute). Much more info on tree irrigation scheduling and hardware at 23 slides from Loren Oki at UC-Davis.
2. Change irrigation schedule
Irrigation schedules need to be changed slowly. For example, if the original schedule included watering 3 times a week, reduce to twice a week for 2 weeks, than once per week for 2 weeks, than one time every two weeks.
Apply 3 to 4 inches of mulch under the tree canopy. Start about a foot from the trunk and extend 2 to 3 feet past the dripline of the tree. This will also gradually eliminate the turf.
4. Provide sufficient water without overwatering
The following guidelines from the San Diego Regional Urban Forestry Council (SDRUFC) are for tree survival during drought. Click on the table for full guidelines (pdf).
Local Certified Arborist Robin Rivet also details options for installing drip irrigation hoses and hardware, and calculates tree watering costs. Article with parts list.
Transition for Trees in Turf
Transition trees from turf irrigation to deep, infrequent watering. With time, the tree's roots will deepen, reducing stress on the tree as watering is reduced. The following timeline depicts the gradual root changes of a healthy tree.
Trees take many years to mature and dead trees are dangerous and expensive to remove. Standing dead trees are also a fire hazard. Turf, on the other hand, is quickly and inexpensively replaced with sod or seed. Remember that trees in all locations are expected to be watered, with the volumes and schedule that keep them healthy.
Watering Young Trees
Newly planted trees usually require more water than established, mature trees. The suggestions above will work for young trees, with increased frequency to retain soil moisture. Once a tree is five-years-old, it can be watered following guidelines for mature trees.
If the turf around the trees is eliminated, the trees will still thrive if watered deeply. Spraying pesticides or diffing out the turn are unnecessary and can damage the trees' roots. The following videos show low-no cost steps of "sheet mulching" with mulch, cardboard and newspaper: 5-minute video, 2-minute video.
Irrigating Urban Trees During Drought, presentation by Loren Oki and Chuck Engels, University of California
Scheduling Irrigation: How Much and When, presentation by Loren Oki
Assessing Irrigation System Performance: Is yours wasting water? presentation by Loren Oki
Preparing Your Trees for the Next Drought presentation by Igor Lacan, University of California