A new, experimental Raingarden at the Royal Botanic Garden Edinburgh (RBGE) has proved its worth during recent heavy rainfall. It may also influence future site management and planting schemes for coping with climate change.
The Raingarden, completed in spring this year, features a range of carefully selected plants in a special mix of soil, compost, sand and gravel. Following the August downpours, the garden successfully absorbed the excess water that fell, reducing floods on nearby paths and capturing rainwater for the benefit of the plants that grow there.
Measuring 20m long by seven metres wide, the Raingarden is a shallow basin that allows water to drain naturally into surrounding ground during heavy rain. It is located at the lowest elevation of an area known as the Birch Lawn which has suffered historically from waterlogged grass, submerged tree roots and flooded paths.
A selection of Scottish native plants and non-native plants, many of which are known to soak up water and thrive in boggy areas, have been used to create the garden. Plantings include primulas and hostas as well as the rare and endangered Alpine Sow-thistle Cicerbita alpina which can only be found on four sites in Scotland and is part of a wider programme at RBGE.
It was created in collaboration with experts from The Water Academy at Edinburgh’s Heriot-Watt University. The Raingarden is being used as a living laboratory to learn more about the trees, shrubs and wildflowers that are best able to cope with occasional temporary flooding, and can help to naturally reduce waterlogging, as well as plants that can withstand other extreme weather events such as drought.
The Raingarden’s unique bioretention system was created by RBGE horticulturists using the Botanics’ existing soil mixed with compost made on site, sand and fine gravel to a specified particle range size. The composition was specifically developed to allow for water infiltration and retention but also to provide organic material and nutrients to support the plants.