Evergreen elm (Ulmus parvifolia), southern live oak (Quercus virginiana), and South American mesquite (Prosopis alba) were irrigated at 75%, 50%, and 33% of reference evapotranspiration for 2 years in Phoenix, Ariz. Each tree was irrigated with twenty-nine 3.8-L·h–1 drip emitters to a depth of 90 cm. Initial trunk diameters were about 4 cm. Water use was monitored by heat balance sap flow gauges and related to canopy volume, projected canopy area, and total leaf area. Oak used more water than elm, and elm more than mesquite under all irrigation regimes. Irrigation regimes had a greater effect on oak and elm water use than on mesquite, but all trees maintained an acceptable canopy regardless of treatment.