Rain Garden Success After Recent Downpours

A new, experimental Raingarden at the Royal Botanic Garden Edinburgh (RBGE) has proved its worth during recent heavy rainfall and may 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 20 metres 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.

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 University’s Dr David Kelly, whose research focuses on finding nature-based solutions to rainwater flooding problems, said: “The Royal Botanic Garden Edinburgh has witnessed changing weather patterns that reflect how climate change is impacting Scotland.  Longer dry periods followed by heavy downpours have proved particularly problematic in terms of maintaining plant health and avoiding localised flooding issues. 

“This experimental garden will be helpful in understanding and planning future site management strategies for coping with an unpredictable, changing climate and ensuring uninterrupted provision of the important public amenity at RBGE.”

RBGE’s Herbaceous Supervisor Kirsty Wilson, said: “Raingarden creation is great news for plant lovers.  Lawns are simply not as effective at soaking up or trapping excess water.  Replacing hard surfaces and grass areas with a mixed selection of herbaceous perennials and shrubs can capture water runoff and increase the wildlife and habitat value of the area.”

“The mix of plants we have chosen will encourage a great diversity of wildlife, providing nectar sources for insects and bees in the summer, and we will leave the stems of the perennials and grasses standing over winter to provide a home for invertebrates and food for seed-eating birds.”

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.

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For further information and images, please contact Sandra Donnelly on 0131 248 1037/07554115908 or Shauna Hay on 0131 248 2900/07824529028

Note to Editors

Plantings within the Raingarden:

The selected Scottish native plants include: Succisa pratensis, Anthyllis vulneraria, Filipendula ulmaria, Knautia arvensis, Cicerbita alpina and Festuca altissima.

The selected non-native plants include: Aruncus gombalanus (China), Gunnera manicata (Brazil), Ligularia fischeri (E Asia), Aquilegia Formosa (Western N America), Primula poissonii (China), Rodgersia pinnata (China) and Hosta sieboldiana (Japan).

A number of established native and non-native trees were already growing at the Birch Lawn, including: A. glutinosa (native), B. pendula (native), C. avelana (native), Quercus robur ‘filicifolia’ (cultivar of a native species), Alnus japonica (Japan), Alnus rubra (N. America), Betula alleghaniensis (NE North America), Betula papyrifera (N North America), B. nigra (USA), Corylus sieboldiana (Japan, Korea), and Populus alba (S and central Europe).