Rose-scented geranium oil is extracted from the shoots (mostly the leaves) of the Pelargonium spp. through steam- or hydro-distillation. To extract less than 0.2% oil, farmers must transport and distil bulky herbage. This makes geranium oil production costly, and high time- and energy-consuming process. To investigate the effect of different paclobutrazol (PBZ) concentrations (0, 100, 200, 300 mg/L of water) on vegetative growth, and oil yield and composition of rose-scented geranium, three pot experiments were conducted. The experiments were conducted in a glasshouse of the University of Fort Hare, Alice, South Africa (located at 25°45′S and 28°16′E, an altitude of 520 m above sea level), between Oct. 2011 and May 2013. The treatments were arranged in a randomized complete block design (RCBD) in four replications. The PBZ was sprayed on the plants at 1 month of regrowth stage. Chlorophyll content increased with concentration of PBZ. The reduction of plant height in all PBZ-treated plants was significant, ranged between 18% and 33%. Plant canopy also reduced by 5% to 23%, and the differences were more noticeable in the plants grown between January and May (summer/autumn season), producing compact plants. Leaf area and internode length reduced as PBZ concentration increased. Paclobutrazol had no significant effect on leaf number, and essential oil yield and composition. This implies that, through applying PBZ, compacted (less bulky) rose-scented geranium could be produced without significant change in essential oil yield per plant and essential oil composition.
Knowledge of essential oil content and composition of leaves of different ages could be used as a guide for the right herbage harvesting stage in rose-scented geranium. Change in essential oil yield and composition with leaf age in rose-scented geranium was investigated in a glasshouse of the University of Fort Hare, during the 2012 and 2014 crop seasons. The topmost five pair of leaves on shoots were separately harvested as treatments. Leaf fresh and dry mass were significantly lower in the topmost and the oldest leaf pair. Essential oil in the topmost pair was colorless; but with advance in leaf age, the oil tended to have a blue-green color. Oil content (on a dry mass basis) from the topmost to the bottom most were about 7.0%, 4.9%, 3.2%, 2.4%, and 1.9%, respectively. Oil yield was consistently the highest in the second youngest pair of leaves, and it progressively declined with leaf age. Contributions of the five leaf pairs from the topmost to the bottom most, in respective order, to the total yield were 19.3%, 22.0%, 17.71%, 12.03%, and 8.5%. The citronellol:geraniol ratio was lower in the young leaves than in the old leaves. Linalool and geranyl formate concentrations were the highest in the youngest leaves, and the opposite was true of isomenthone. The current results indicate shorter regrowth cycles would increase essential oil yield and quality of rose-scented geranium, provided an efficient harvesting technique was innovated.