Although I am writing this at a time when the challenge of keeping a conservatory, shed, extension, garage or any other garden outbuilding cool in the summer heat seems a little premature, I can only hope that you are reading this in warmer – and more pertinent – weather.
This post, though, has been triggered by some interesting research* just published by the Universities of Sheffield and Reading into the effects of planting a Cherry Laurel hedge (Prunus laurocerasus) against an outside brick wall. Their findings show conclusively that the temperature of a wall behind the Laurel hedge is up to 10oC (1ooF) lower than a corresponding bare wall in the same conditions. Additionally, the air adjacent to the walls was 3oC cooler than nearby bare walls. On sunny days, walls screened by plants were significantly cooler between 11:00am and 6:00pm, with the greatest differences in mid-to-late afternoon.
So, if you want to keep your garden office, for example, cool and don’t want the financial costs or energy consumption of air conditioning, you know what to do.
The Cherry Laurel is particularly effective because, the research has revealed, it cools through both direct shading and evapotranspiration (the combined effect of evaporation and plant transpiration), while climbers like ivy, jasmine and honeysuckle cool by shading only and fuchsia, for example, cools by evapotranspiration only. The research team also looked at plants (like lamb’s ear) that cool by reflectivity.
Of course, any plant on or near an outside wall will also have an insulating effect in colder weather, though the research did not quantify it. Either way, though, this is yet one more example of the versatility of hedging
*The research was conducted by HTA-funded PhD student Jane Taylor, led by University of Sheffield senior lecturer in landscape management Ross Cameron using a replicated wall system outdoors.