Abstract/Summary

Flooding risk in urban areas has increased due to the expansion of impervious surfaces, removal of garden vegetation, and predicted rise in heavier rainfall events due to climate change. Domestic gardens cover up to 30% of UK urban areas, so plants they contain could have a significant environmental impact, with the potential to retain rainfall, reduce runoff and mitigate localised flooding. The hypothesis was tested that plants with certain traits, including higher evapotranspiration rates and hairy leaves, or mixtures of plants with diverse traits, would provide greater rainfall retention compared to certain monocultures and non-vegetated surfaces. To test this, popular perennial garden plants representing these traits were grown in monocultures or mixed planting and exposed to simulated rainfall and short-term flooding. Species with higher transpiration rates and/or hairy-leaved canopies (such as Oenothera lindheimeri ‘Whirling Butterflies’), or planting combinations including them, provided greater rainfall retention compared to planting without these traits (for example, Oenothera gardens reduced runoff by 6-20%). Plant function, and therefore ecosystem service provision, of higher transpiring ‘drought-tolerant’ Oenothera and Verbena bonariensis was unaffected by flooding, and increased the flooding tolerance of companion plants when grown in mixed pairs, reducing substrate moisture by t 79% compared to monocultures of lower transpiring plants. Gardens are privately designed spaces, therefore people’s preferences and willingness to change is also crucial to maximise the environmental benefits of planting. An experimental survey found that a combination of environmental information and trait-based planting recommendations based upon the preceding chapters, made participants more willing to change preference in favour of plants linked to greater environmental benefits. Climate change concern also increased respondents’ positivity towards pro-environmental planting by 141%. Simple planting recommendations and concern for the climate were both highlighted as key avenues to explore for influencing plant choices and improving the potential environmental benefits of gardens.