Investigating The Planting Potential For Urban Rain Gardens: Plant Selection, Establishment and Performance

Rain gardens refer to planted shallow depressions widely adopted in urban areas to integrate vegetation and soil to mitigate the increasing urban stormwater issues, and are also perfect spots to adopt taxonomically diverse plantings to provide habitat values and aesthetics. However, few studies to date have successfully reflected the horticultural aspects and planting potential in rain gardens. This PhD is divided into three separate studies, which aim to characterise the success of a range of potential plants with different traits and different geographical origins in typical rain garden conditions and to access the relative hydrologic performance of different vegetation types to make informed planting decision, as well as to investigate the establishment of low-input in-situ sown vegetation in rain gardens. The first study tested a range of potential native and non-native forbs and grasses in simulated rain garden cyclic flooding and extended drought. Results confirmed existing expectations with respect to which plants would be best suited to the bottoms, slopes and margins of periodically-inundated rain gardens. In the second study, experimental rain gardens planted with taxonomically diverse plantings composed of forb-rich perennials, mown grasses and bare soils were tested with artificial rainfall. The forb-rich perennial mixes featuring greater species richness and structural diversity consistently provided the best hydrologic performances, and can therefore be recommended for use in rain gardens. In the third study, in-situ sown forb-rich plantings were created in practical rain gardens with the involvement of two low-impact weed control measures including the use of felt mats and mulching. Mulching shows significant effectiveness on weed control, whereas no valid conclusion could be drawn on the effectiveness of felt mats due to the contamination of the potentially weedy compost mulching. The ‘dry-wet’ moisture gradient in rain garden depression was determined to significantly influence the establishment of sown plantings.