Gardening in a changing climate
Mediterranean plants: the key to tomorrow’s gardens?
Claire King is working on an RHS-funded studentship at the University of Reading to investigate the effects of waterlogging on Mediterranean plants. This study aims to understand how such species are likely to behave in the UK under the projected future climate-change scenarios.
Hotter, drier summers are predicted for much of the UK. This has led to the notion that future plantings may rely strongly on Mediterranean species, due to their adaptation to drought and high temperatures. The climate forecasts, however, also predict wetter winters, and such species may not tolerate long periods of winter rainfall and flooding. In contrast to Mediterranean soils, which tend to be stony and free draining, UK soils are often composed largely of clay or silt and this exacerbates problems of poor drainage.
Experiments were set up to determine the effects of waterlogging on a range of widely-available Mediterranean garden plants (Lavandula angustifolia (right), Cistus, Salvia officinalis and Stachys byzantina) at different seasons. Interestingly, the plants proved more sensitive to flooding in spring and summer; as the plants recovered, the penalties to growth were most severe at higher temperatures.
About one-third of Salvia officinalis (sage) and Cistus x hybridus (syn. C. x corbariensis) died in summer; on average, the test plants’ growth was reduced by more than two-thirds. This suggests that roots are suffering directly from a lack of oxygen (anoxia), caused by higher respiration rates in warmer weather.
In contrast, survival rates were relatively good during the cooler winter months - for example, plants survived flooding for 17 days or more. There were major differences between species too, with sensitive plants such as Salvia having poor root growth after flooding, compared with the more tolerant Stachys.
Work is continuing to investigate the strategies Mediterranean species have adopted to counteract waterlogging.