
Rain gardens are becoming increasingly popular in our gardens as they provide an attractive aesthetic and diversity of habitat as well as offering a highly practical alternative to the use of water in our gardens and designed spaces. Whats more they can work in virtually any size of garden. With low environmental impact they challenge the more traditional view of water, so often regarded as either as an individual ‘feature’ effectively divorced from the rest of the landscape or, especially in the case of urban stormwater, simply an irritation to be drained or culverted away at the earliest opportunity.

In essence rain gardens are planted areas of lower lying ground, swales, dips or depressions, into which water collects during rainfall or flood. The rain garden then acts as a temporary holding area for the water which gradually seeps away into the ground. As with a green roof, a rain garden can be seen as a natural sponge; soaking up excess water in a relatively short space of time to release it more slowly over a longer period.


Rain gardens are therefore periodically both very wet and very dry, which in horticultural terms may appear as something of a contradiction. But in the natural world such changeable conditions are frequently encountered where water and land coincide and so a range of plants such as carex, juncus, luzula and deschampsia have adapted to take advantage of these sometimes challenging environments.


In our natural systems these plants are generally found in damp and wet areas such as water meadows and stream sides. Such places are frequently wet but as the seasons alter streams and wet areas can become quite the opposite until the moisture returns. To successfully colonise these places some plants have learned to cope with the sometimes wet, sometimes dry environment, and this successful strategy can be used to great effect in our designed spaces and especially when planting rain gardens.

Our Rain garden at Knoll consists of four linked swales that run alongside the immediately adjacent Dry meadow. The garden soil is for the most part a very dry sand though with heavy rainfall local flooding can occur and the rain garden was sited in part to help alleviate this problem from over a wider area. With the swales set at a lower level than the surrounding Dry meadow any excess water would flow off the meadow and into the rain garden.

Each of the four separate but linked swales were planted with a different mix of plants including; Acorus Golden Edge, Carex divulsa, Calamagrostis x varia, Luzula Snowflake, Luzula Marginata, Deschampsia Goldtau, Deschampsia Mill End and Molinia Poul Petersen.

Although the rain garden palette was radically different from that of the Dry meadow, plants from both areas were allowed to mingle at the margins to help merge one area into the other. The winter rainfall soon proved the value of the rain garden. Flooding of nearby pathways was virtually eradicated and while often full the individual swales collectively held the volume of water; releasing it into the ground over a period of time.

Simply by altering the ground levels this project provided a low impact solution to local flooding and created a distinctive growing environment that is as attractive to wildlife as it is to the gardener.
