Reduced nutrient and water availability to Hibiscus rosa-sinensis 'Cairo red' as a method to regulate growth and improve post-production quality

The intensive use of water, fertiliser, and chemical growth retardants in horticulture reflects a need for developing new and more environmental suitable production methods to reduce the usage of water and fertiliser, and to reduce the use of pesticides for growth control. We have focused on drought as a single stress factor or combined with reduced phosphorus (P) or reduced nitrogen (N) availability to regulate the growth of Hibiscus rosa-sinensis. Drought stress was applied as cyclic drought, alternating between container capacity and drought to visible wilt (-650 to -800 hPa as measured with tensiometers placed in the growth substrate). We used a P buffer technique (Compalox®-P) to maintain a predetermined and stable P concentration in the growth substrate. Reduced N was either provided as a constant low N fertigation or as a dynamic supply where the N availability varied throughout production according to plant demand. Drought as a single stress factor reduced plant height by 32 % and low P reduced plant height by 15 % as compared with the control. Combining drought and low P did not reduce the plant height much further. Continuous low N availability reduced plant height by 21 %, whereas there was no clear growth regulating effect of dynamic N availability. Post-production evaluations showed that chemically growth regulated plants had by far the highest percentage of senescent flower buds throughout the post-production evaluation test compared with plants from all other treatments. Reduced P and N availability during production improved the post-production stress tolerance by significantly reducing the number of senescent flower buds and increasing the number of open flowers compared with chemically growth regulated plants. Several cycles of drought reduced post-production quality compared with control plants but improved it compared with chemically growth-regulated plants. The potential benefits of using combinations of reduced water and nutrient availability as methods to reduce the use of pesticides for growth regulation in horticulture, and how these production treatments influence the post-production stress tolerance are discussed.