A series of experiments were conducted to determine the ranges of irrigation frequency and N and P fertilization regimes that produce ivy geranium (Pelargonium peltatum L.) plants of optimum commercial quality. Two cultivars, `Sybil Holmes' and `Amethyst', were grown. Data collected included fresh and dry weights, ratings, leaf area, height, width, ratings, and nutrient tissue content. Individual pots were weighed daily and irrigated when weight of pots dropped by 15%, 30%, 45%, or 60% of container capacity (CC). Leaf water potential was measured using a pressure chamber. At both mid and end of crop, plants irrigated when pot weight dropped by 30% of CC were under least water stress (e.g., water potential of –7.0 to –4.7 MPa). Irrigation frequencies at 15%, 45%, or 60% of CC had similar water potentials (e.g., –9.9 to –9.1 MPa). At 15%, a plausible explanation of the stress is that oxygen was limiting in the root zone due to water-logging; at 45% and 60%, water was the limiting factor. Single factor experiments with N at five concentrations ranging from 2 to 32 mm and P at five concentrations ranging from 0.08 to 2.56 mm were conducted. Quadratic equations were fit to curves of growth responses plotted against concentration of N or P applied. As an example of results, N fertilizer rates of 16 and 32 mm for `Amethyst' resulted in similar, commercially acceptable dry weights (37g), but different N tissue concentrations of 3.4% and 3.9% respectively. For `Sybil Holmes', N fertilizer rates of 10 and 26 mm resulted in similar dry weights (21g) but different tissue concentrations of 2.8% and 3.4%, respectively.
Effects of Irrigation Frequency on Growth Responses of Indoor Foliage Plants
