The 2009 ASHS Annual Conference

The effect of root medium water status, supplemental calcium (Ca) fertilization and vapor pressure deficit (VPD) on the occurrence of the physiological disorder oedema was evaluated on ivy geranium (Pelargonium pelatum L’Her ex Ait) in two greenhouse experiments (summer and fall). Cultivars in the experiments included ‘Amethyst 96,’ ‘Lambada,’ and ‘Sybil Holmes.’ Root medium water status treatments included dry (plants were re-watered when pot weight dropped by 65% from container capacity), optimal (30% water loss), wet (15% water loss) and saturation (pots were placed in a saucer filled with water at all times). Supplemental Ca was applied at rates of 0 and 300 mg∙L^-1 from CaCl₂ at each irrigation and weekly to saturated treatments. Two VPD environments were created by building tent-like structures out of PVC and plastic film. The high VPD tent had plastic film only on the top, and fans blew over the plants at all times. The low VPD tent had plastic film on all surfaces except the bottom, and mist supplemented humidity. At harvest, all plant leaves were scanned using a flatbed scanner to quantify % leaf area affected by oedema. Growth, measured as fresh weight, dry weight and leaf area was different based on the water status treatments with dry consistently smaller than the other treatments. Water status, Ca and VPD had no effect on the leaf area damaged by oedema in either experiment, but cultivar, water status, and Ca did influence % damage in the summer experiment. The traditional recommendation that growers produce ivy geranium ‘on the dry side’ to minimize the occurrence of oedema should be reevaluated.