Rain gardens are one of the hottest topics in garden design in the US - yet they have hardly hit the headlines here. This is surprising, because they are one of the most exciting (if a little daunting) developments to come out of the 'eco gardening' scene.
RBC Rain Garden, London Wetland Centre (photo: Catherine Starling)
Rain gardens are simply depressions or slightly sunken areas where rain water can be collected. They are absolutely not ponds or bog gardens - the whole intention is that water is allowed to drain away into the soil. In dry periods they will be dry, and look no different from any other area of the garden.
However, in wetter times, water may collect on the surface, giving the appearance of temporary puddles. Plants to be used in rain gardens must there be able to withstand some wetness, but be able to grow in normal conditions for most of the time: rudbeckias, irises, miscanthus grasses, astilbes, many euphorbias: this list is very long.
The rain garden idea was initially developed in the States around 15-20 years ago, and has spread rapidly. There is also a very big take up in Australia and New Zealand.
The concept was first promoted as a way for gardeners to contribute to reducing the growing problem of severe flash flooding in towns and cities. The idea is that the garden soaks up as much, if not all, of the rainfall that falls on it, preventing the excess runoff running into the drainage system.
In times of very heavy rainfall, all the runoff coming from roofs, paths, pavements, roads, and all the other sealed surfaces, can simply overload the drainage system, resulting both in large areas of flooding, but also, often, the discharge of untreated waste water into rivers and streams. What with issues such as the paving over of front gardens, with the increased run-off into the streets this causes, we're becoming all too familiar with this issue in the UK too.
Rain gardens aim to prevent this happening, by using areas of planting to soak up that runoff. The underlying slogan for the movement is 'disconnect your downpipes!' - cut off the pipes coming from the house gutters, and divert the water into the garden. Paths can be drained off into planting, and large areas of paving or driveway replaced with more permeable materials.
The great thing about rain gardens is that it is all about the house, the garden, and the domestic scale (unlike 'sustainable urban drainage schemes' which are much more about large-scale engineering).
But the very best news is that this will only work with planting - you need the areas of soil and plants to soak up that rain water. So this is where gardeners and garden designers come to the very forefront of tackling climate change. But more than this - gardens with lots of good planting are, automatically, far better for wildlife, and, I am convinced, much better for people too!
I think gardens like this are so much more satisfying than gardens produced purely for ornament or decoration alone. There are so many more stories to be told; so many more interesting and exciting features to be included, and above all, there is the knowledge that your patch is contributing to something far larger than purely your own enjoyment.
If you want to see a rain garden in action, take a look at the new Royal Bank of Canada Rain Garden I designed at the Wildfowl and Wetland Trust London Wetland Centre. As a follow-up, we're also creating a full-scale rain garden as one of the main show gardens for the RHS Chelsea Flower Show 2011.
And if all this has whetted your appetite to create your very own rain garden, take a look at this step-by-step guide to how it all works:
There's more, including a downloadable leaflet on rain gardening, on the WWT's website.
Dr Nigel Dunnett is Reader in Urban Horticulture at the University of Sheffield. He is author of several books on sustainable garden design and planting, and is currently horticulture and planting design consultant for the London 2012 Olympic Park.