Rain gardens

Rain gardens

What is a rain garden?

A rain garden can come in several different formats; either a shallow depression or a raised planter. They are designed to capture rain water flowing off roofs and slow the flow of the water back into drains and eventually watercourses.

Rain gardens can help to reduce flooding by storing rain water and reduce pollution by filtering water, whilst also allowing you to create a wildlife friendly feature for your garden that may need less maintenance and watering.

Rain garden

Why make a rain garden?

Extensive areas of sealed surfaces like tarmac in towns and cities cause problems in heavy rainfall, with drains often becoming overwhelmed. When this happens localised flooding can occur, damaging property and blocking streets. In some cities water run-off into drains may wash oil, heavy metals and other pollutants into watercourses, damaging the plants and animals that live in aquatic environments. 

These problems have become worse as towns and cities have grown and are expected to be exacerbated by climate change, which is likely to bring about more frequent and heavier downpours. One of the most effective ways of tackling these problems and adapting to climate change is to increase the quantity and quality of vegetation and soils in towns and cities.

Rain gardens help gardens to deal more effectively with rainfall, but they also filter and clean run-off. By providing more rain gardens we will be able to reduce the risk of flooding and rain gardens can be planted to attract wildlife, such as pollinating insects, and reduce maintenance costs.

Rain garden example

How to make a rain garden?

Choose the right location
Rain gardens are best located at low points where surface water will flow. However, the location might be determined by the downpipes from your guttering, ideally below a downpipe and near an existing drain. Check guidance on the best place to position your rain garden.

How big should my rain garden be?
The bigger the better, however if space is an issue then any size rain garden will help. Ensure you construct an overflow to take excess water back to the drain to avoid flooding.

Hand digging is best when constructing a sunken garden to ensure you don’t hit any buried existing services. If constructing a planter-style rain garden, ensure there is a solid bottom to retain water. Layers of substrate should be approximately 26% gravel at the bottom, next a 13% sand layer, then a 53% sand/soil mix and finally 7% gravel mulch on top. Work out exact quantities based on the size of your planter and consult a detailed guide (see back of leaflet for references). Ensure your overflow pipe is at least 100mm above the top of the gravel mulch and 100mm below the top.

Consider how much sunlight your garden will get and how much water (a smaller garden will hold more of your roof’s rain water). You could plant shrubs such as dogwood and guelder rose, or smaller flowering plants such as bugle, yellow flag iris, ferns, sedges and grasses.

Your garden may need weeding occasionally and some plants might need replacing. Keep checking your overflow pipes to make sure they are draining freely and not blocked up.

Gloucestershire Wildlife Trust are working in partnership with The EnvironmentAgency and Gloucester City Council to create healthy, functional watercourses for people and wildlife. As part of this work two demonstration rain gardens have been created in Gloucester. An example of a planter-style rain garden can be seen at Abbeydale Community Centre and a sunken rain garden has been created outside the Matson Baptist Church in Gloucester.

To find out more, including how to make your own rain garden, visit:
• environmentagency.blog.gov.uk and search for ‘rain gardens’

To find out more about river improvement works in Gloucester please visit
consult.environment-agency.gov.uk and search ‘Gloucester rivers’.