Morphology and Irrigation Efficiency of Gaura lindheimeri Grown with Capacitance Sensor-controlled Irrigation

Gaura lindheimeri Engelm. & Gray ‘Siskiyou Pink’ (gaura) and Phlox paniculata L. ‘David’ (garden phlox) were grown for 5 weeks in substrates irrigated at volumetric water contents (Θ) of 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or 0.45 m 3 ·m −3 using a capacitance sensor-controlled irrigation system. Volumetric water contents of the substrate measured by the capacitance sensors controlling irrigation were correlated with measurements with a separate handheld meter ( r 2 = 0.83) and with volumetric water content set points throughout the study ( r 2 > 0.98). Only 3.8 (at an irrigation set point of 0.10 m 3 ·m −3 ) to 53 L (0.45 m 3 ·m −3 ) of water was used to irrigate gaura and phlox and 0 to 7.74 L of this water leached out of the substrates. Significant leaching occurred only at Θ set points of 0.40, or 0.45 m 3 ·m −3 . Gaura had shorter and fewer branches and reduced dry weight when grown at lower volumetric water contents, but plants irrigated at set points above 0.25 m 3 ·m −3 were large enough to be marketable. Gaura may be grown with capacitance sensor-automated irrigation using water efficiently and minimizing or eliminating leachate and thus nonpoint source pollution.