The development of a smart irrigation control system for living wall system

Most recent studies of Living Wall Systems (LWS) have emphasized their benefits in terms of aesthetics, improving urban vegetation cover and thermal benefits. However, few have focused on the plant water consumption and irrigation management. LWS often use a fixed irrigation period (e.g., 5 min/day) rather than designed based on actual plant requirements and their adaptation to water availability. The aim of this research was to investigate the potential of irrigation controllers that regulated water availability more precisely, and determine how plants respond. Maximum growth is not always desirable in LWS as this relates to greater maintenance (and hence costs) with trimming and pruning requirements. Thus, the research investigated if drier irrigation regimes could control excessive plant growth whilst maintaining quality. Differential irrigation regimes (‘wet’, ‘medium’ and ‘dry’) were set up to determine their effect on growth, leaf number and aesthetic quality. Comparisons were made across two different climates (Jingmen, China and Sheffield, UK) and at different phases of the annual growth cycle. Four taxa (Hosta, Vinca, Heuchera and Hedera) were included in the study, with plant communities being composed of single species or mixed species combinations in a LWS cell unit. Results showed that plant growth and quality was determined by the irrigation treatments. It was feasible to control growth and retain respectable plant quality, although optimum regimes for this could vary with time, species and location. Experiments with single species per cell, suggested overall the best regime for Sheffield was a medium irrigation treatment (from 40% to 65% soil moisture content) during May-June followed by a wet treatment (from 65% to 90% soil moisture content) during July-October. For Jingmen, a medium to wet treatment during May to June and a medium treatment during July to Oct was considered the best compromise. Drier regimes however, were considered better when plant species were mixed together, with dry treatment (from 15% to 40% soil moisture content) during May to June and the medium treatment during July to August being recommended for both Sheffield and Jingmen. Some LWS systems are subjected to heavy shade. A small sub-experiment explored the relationship between shading and irrigation level. Based on the treatments imposed shade seemed to have a greater impact on growth than irrigation level, but further research is required to find critical levels of shading and how that implicates plant water use. The author developed a model for controlling irrigation in a mixed species LWS and an original framework for a smart irrigation control system has been provided within the thesis.