Daily Water Requirements of Petunias as a Function of Plant Age and Environmental Conditions

Most ornamental plant growers use excessive irrigation water to prevent the risk of unwanted drought stress. Quantifying the daily water requirements of greenhouse crops may provide a useful tool to reduce excessive irrigation. Two petunia (Petunia × hybrida) cultivars, ‘Single Dreams Pink’ and ‘Prostrate Easy Wave Pink’, were grown in three different size pots (diameters = 10, 12.5, 15 cm) to quantify their daily water use for 6 weeks. A datalogger with dielectric soil moisture sensors was used for automated irrigation control to maintain the substrate moisture content at 0.40 m³·m^-3, and every irrigation event was recorded by the datalogger and used to calculate daily water use. On overcast days early in the experiment, plants used only 4.7 to 8.8 mL/day. The maximum daily water use of ‘Single Dreams Pink’ was 63, 96, and 109 mL in 10-, 12.5-, and 15-cm pots, respectively. ‘Prostrate Easy Wave Pink’ used more water (up to 104, 168, and 209 mL/day in 10-, 12.5-, and 15-cm pots), because of their larger size. Daily water use was modeled as a function of days after planting, daily light integral, and maximum vapor pressure deficit (0.75 < R² < 0.90). The cultivars and pot sizes affected the model coefficients. Plants in larger pots used more water (P < 0.001) and had higher dry weight and larger total leaf area (P < 0.001) than those in smaller pots. These models, describing the daily water use as a function the plant age and environmental conditions, can be used to predict the water requirements of petunias in greenhouses. This use of such models can improve irrigation scheduling in greenhouses, resulting in water, fertilizer, electricity, and labor savings.