How to build a rain garden
There’s no doubt that our weather is getting wetter and warmer in the UK. Gardeners need to find new ways to counter these climate extremes and conserve precious natural resources, such as rainwater.
Any leafy garden will act as a soakaway for rain. Lawns, trees and diverse planting help to absorb and divert water to where it’s needed, reducing the chances of flooding. But what if you could make a more deliberate attempt to preserve water?
Benefits of a rain garden
A rain garden mimics the natural action of a forest or meadow by capturing rainwater in a plant filled shallow ditch. Fed from a downpipe on a roof (or even a driveway or street), the rain garden fills with a few inches of water when it rains, and slowly diverts and releases water that would otherwise go into the drain. This protects rivers and streams, but also offers a colourful, low maintenance and attractive garden for you and for wildlife.
Rain garden plants are carefully chosen to tolerate waterlogged or dry conditions, and tend to be deep rooted perennials. Their roots allow water to drain slowly, rather than quickly. Flowering plants also attract beneficial pollinators, such as under threat bumblebees and butterflies.
Studies show rain gardens can absorb 30-40% more water than a lawn, and can help prevent soil erosion by slowing heavy rainfall. They help reduce flooding, but because they store water more successfully, they allow your garden to better survive drought. As a natural filtering system, they also absorb sediments and pollutants, and release fresher, cleaner water.
Step-by-step rain garden 🔗
Our head gardener Emma O’Neill, explains how to make a rain garden in your own growing space.
1. Plan your space
Aim to build your rain garden when the soil is dry and not waterlogged. Ideally, choose a partially shaded, well-drained area below a roof, so you can siphon water. Ideally, you want your rain garden to be 20% of your roof area, but even a small ditch can help mop up floodwater. Aim for it to be at least 10ft from your home, and away from utilities. We linked our rain garden to a downpipe and water butt, but you could also use a downpipe diverter. Alternatively, simply note the natural low spots in your garden, where water is already collecting, and site your rain garden there.
2. Dig your ditch
Dig a shallow ditch with flat bottom, 10-12cm deep. Time how long the area takes to drain before planting, to ensure it can hold water and drains slowly.
3. Line your ditch
Cover the base of your ditch with 5cm of well-rotted compost (preferably homemade). This will help to hold moisture in the summer. Be careful not to tread on the soil in the base of your ditch so it remains uncompacted. Make a channel or rill on one side, leading from the downpipe. Line with gravel and stones to stop soil being washed away. We also added one to the other end of our rain garden to slow down drainage and help with overflow.
4. Fill with plants
Plants in the base of the ditch need to tolerate wet conditions, sometimes standing in water for up to 48 hours, while those on the edge need to be able to withstand drought. We recommend the following plants: marsh cranesbill (Geranium palustre), devil’s bit scabious (Succisa pratensis) and cardinal flower (Lobelia cardinalis), but you could experiment with yellow flag iris, day lilies and purple loosestrife. Water your plants well for the first few months while they get established. After this, they won’t need watering.
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