Our Community Growing Project frequently receives enquiries from people who want to make their gardens more sustainable. Questions about rain gardens, for example, or wildflower meadows. Sometimes it can be a challenge to work out how to scale these ideas so that they work in your own back garden. In this new series of posts, we will respond to some of these queries. If you have a question you would like us to feature – whether related to food growing or sustainable gardening in general – please contact Nicky. If you have tried these ideas at home, let us know how it goes!
This month we discuss, “what is a rain garden, and how do I create one at home?”
Essentially, a rain garden is a hollow in the ground that rainwater is directed into, with a planting scheme that can cope with periods of both flooding and drought. In recent years, many local authorities have removed sections of concrete pavement and replaced them with planted areas, allowing water to drain naturally into the ground. This enhances biodiversity and reduces pressure on drainage systems. Removing an area of concrete is, of course, a great way to make an area more sustainable, but it’s not necessarily a cost effective or practical solution in your own garden. Nevertheless, you can create a rain garden at home without carrying out any hard landscaping.
Example of a rain garden at home (Source: How to make a rain garden – WWT)
One of the easiest ways to create a rain garden at home is to simply place a planter under a downpipe and allow the water to flow into the planter. However, if you want to create something more extensive, you will need to do a bit of planning. First, you need to think about the layout of your garden. Where are the impermeable, hard surfaces (rooves, patios etc) and where are the soft, permeable surfaces (flower beds, lawns etc)? The idea of a rain garden is to divert water from the hard surfaces, which might currently be running straight into urban drainage systems, into the soft surfaces, so it can drain away naturally. You then need to think about how to intercept the run-off from the hard surfaces; by using a water butt, for example. After that, you’ll need to find a way to connect this to a hollow – you might dig a rill, or attach another pipe.
When digging the hollow, there are a number of things that need to be taken into consideration. The hollow should be on a well-drained area, and should not be located in full shade, or on a steep incline. It is advised to seek expert advice if locating it 5m or closer to a building, to ensure that the infiltrating water doesn’t do damage to the foundations. You also need to be mindful of tree roots, and underground pipes. In order to test whether the soil is suitable, you can excavate a small hole and fill it with water, and observe how long it takes to drain. Ideally, the water needs to infiltrate at a rate of 1.25 to 5cm per hour. If it takes longer, the site is not suitable. Ideally, the size of the rain garden should be 20% of the area of the impermeable surface the water is coming from. A smaller rain garden will still work – it will just flood more frequently.
Once you have decided on the location and size of the rain garden, you can dig the hollow. Use the soil to create a berm around the edge, with a gap for the water to run into it. You can then incorporate organic matter such as leaf mould or manure into the area, to aid drainage, and re-fill it.
The garden is now ready to plant, and choice of plants is important, as they need to be able to withstand both flooding and drought conditions. Plant choice will also be dictated by the size of your hollow; Sambucus nigra, for example, is a good choice, but it does get very large. Ajuga reptans is a much smaller plant that is great for ground-cover. There is a lot of advice online about what plants might be suitable – WWT’s website is a good starting point.
Once you have established your rain garden, observe how it is working and make any tweaks necessary. Maintenance will essentially be the same as for any other planted area. And remember to sit back and enjoy the sight of pollinators buzzing around your new, sustainable planting scheme!
Header image: Rain garden in a pavement (Source: The Ranty Highwayman: Rain Gardens)
Are you looking for more information on flood resilience? Barnes Common is a partner in the Community BlueScapes (CBS) project, alongside the London Borough of Richmond upon Thames and WWT. We are coming together to create healthier neighbourhoods in the Beverley Brook catchment in Richmond and ensure our communities are flood and weather resilient in the near future. Find out more on the CBS website here.