When it rains it pours – rainfall retention within the canopy of popular garden plants

Increased impermeable surfaces and decreased vegetation in urban areas lead to surface water accumulation. Domestic gardens account for approximately 30% of UK urban areas, therefore the careful selection of garden plants that can either retain water in their canopies or remove water quickly from the soil are helpful for homeowners aiming to reduce localised flooding. Planting design and plant combinations can play an important role in this research. Combinations of popular garden plants Erysimum and Oenothera in monocultures and mixtures were subjected to controlled rainfall application to determine the efficiency of the plants to reduce rainwater runoff during both summer and winter months. We investigated whether an evergreen plant (Erysimum) can reduce water runoff and increase rainfall retention within the canopy when planted in combination with a deciduous plant in winter, or if a hairy-leaved deciduous plant (Oenothera) in a combination can improve canopy retention in summer. Results indicated the traits of the plants (in this case hairy leaves or stems of Oenothera) increased rainfall retention capacity within the canopy more than evergreen foliage alone (Erysimum) in either summer or winter. It was also found that mixing plants, when one has beneficial traits, could alleviate the impact of a poorly performing monoculture, which could be beneficial for improving the performance of garden planting beds and reducing localised flooding.