249 Effects of Shading and Moisture Stress on Yield and Oil Quality of Hydroponically Grown Rose Geranium M.M. Sedibe Central University of Technology School of Environmental Health and Agriculture P/ Bag x20539, Bloemfontein, 9301 South Africa J. Allemann Department of Soil, Crop and Climate Sciences University of the Free State P.O. Box. 339, Bloemfontein, 9300 South Africa Keywords: osmotic pressure, flavouring agent, oil quality, greenhouse, moisture stress Abstract Rose geranium oil is used as a flavouring agent in many major food items and alcoholic and soft drinks. Relatively high radiation levels occur in South Africa during summer months and some hydroponically grown crops may need shading for optimum production. This study was conducted during spring and summer to evaluate the effects of shading and moisture stress on growth, oil yield and oil quality of rose geranium. A split plot experimental layout was assigned in randomized complete block design. Treatment with 0, 20, 40, 60 and 80% shading were allocated to the main plots. Subplots were exposed to two moisture stress levels of 0 and -0.15 MPa of osmotic pressure. The results show that rose geranium performs well when grown at a shade netting of 40%, where the number of branches, foliar fresh and dry mass, branch:height ratio as well as the oil yield peaked. Proline content was significantly higher at a low level of shading, where high levels of radiation were found and where moisture stress was applied. However, moisture stress did not affect any of the quality parameters measured for rose geranium oil. Most of the chemical substances produced at 40% shading level were of good oil quality. This study shows that 40% shade should be used to grow rose geranium in summer. INTRODUCTION The oil of rose geranium is used as a flavouring agent in many major food items, as well as in alcoholic and soft drinks. Fresh rose geranium leaves infuse a rosy flavour to desserts and jellies (Gough, 2002). The oil is also used as an important ingredient in the perfume and cosmetic industries (Kulkarni et al., 1997). Although rose geranium plants grow well under full sunlight in summer, lower light intensities may be beneficial to improve plant growth and yield. Herb-, oil yield and oil quality decreased when rose geranium was grown under tree shade (Kaul et al., 1997). The total radiance at the upper boundary of the atmosphere is 1360 J m -2 s -1 . Most of this radiation is lost by absorption and scattering caused by dust, water vapour, CO 2 and O 3 in the atmosphere. The average midday radiation in Bloemfontein during the summer months varies from 500 to 800 MJ m -2 s -1 . Most greenhouse growers in South Africa use lime or removable paints to reduce radiation in greenhouses and plastic tunnels. More expensive structures with light reflecting screens (nets) are also used for high-income crops (Combrink, 2005). The aim of this study was to evaluate the effects of shading and moisture stress on yield, oil yield and oil quality of rose geranium. MATERIALS AND METHODS The trial was conducted at the West campus facility of the University of the Free State in Bloemfontein, South Africa, during spring and summer seasons. The facility is located at latitude 29°06’S and longitude 26°18’E, and an altitude of 1351 m a.s.l. An automated weather station, located at the facility was used to collect weather data throughout the trial period. A completely randomized block experimental design with a split-plot experiment Proc. IS on Medicinal and Aromatic Plants Eds.: N. Chomchalow et al. Acta Hort. 1023, ISHS 2014