Here, Nicky Roeber, Online Horticultural Expert at Wyevale Garden Centres, tells us what we need to know about a rain garden and how we can build one at home.
A rain garden is a small garden, usually planted in a shallow dip, which collects rainwater runoff from hard surfaces like roofs. They’re an eco-friendly way to remove excess water from around your home and can even filter out the harmful pollutants that rainwater collects from outdoor surfaces. This means that less of these pollutants will enter your drainage system and make their way into local streams and ponds. Want to create one of your own? Just follow my advice to plant a rain garden at home.
Where should you plant your rain garden?
Ideally, your rain garden should be planted in full sun or partial shade on a slight incline of 10% or less and in an area where the soil can drain quite easily. You can test how well the soil will drain by digging a 25cm hole and filling it with water. When it empties, fill it back up and time how long it takes to drain completely. For a successful rain garden, the drainage rate should be between 1.25–5cm per hour. If you’re worried about your drainage level, you can mix in some gravel or stones to aid it, but if your garden has heavy clay soil, it’s probably best to find a different location.
To avoid damp and flooding in building foundations, you should try to plant your rain garden at least 10 feet away from your house. It’s also important that you check that there are no tree roots or underground pipes or wires where you plan to build. You can check this by digging carefully in the area. If the ground is clear, you are free to plant your rain garden.
How big should your rain garden be?
The width of your rain garden will vary based on the amount of space you have to work with, but to avoid it overflowing, it should be around 20% of the size of the roof area. The depth of your rain garden depends entirely on how quickly it will drain. As a guide, it should be between 10 and 20cm deep and the surface should be level.
How do you build your rain garden?
Now here comes the fun part — start digging! It’s important to remember not to compact the soil base of your rain garden, as this will curb drainage. As you’re digging, don’t get rid of the excess soil, as this can be used as a ridge around the lower edge and the sides of the garden to keep it watertight. This ridge should be about 30cm wide and 10cm tall, and well-compacted. You should also leave a slight gap in the ridge around the lower edge and fill it with gravel to allow any excess water to drain out without washing away the soil. Then, using a trail of bricks, create a path to guide the rainwater from the drainpipe to your garden. Again, you can add some gravel to the entrance of your rain garden to avoid washing away the soil.
What kinds of plants should be in your rain garden?
The kinds of plants you add will depend on your soil and local average rainfall. If your soil will take a while to drain or you live in an area that gets a lot of rain, your garden might get slightly waterlogged, which means you’re going to need to choose moisture-loving plants that can handle being in damp areas for a few days. These kinds of plants include yellow iris, ferns, pendulous sedge, cardinal flowers and arum lilies.
If your rain garden will drain well, but might see a few dry spells here and there, it’s best to pick plants that can tolerate both wet and dry conditions. You could choose plants such as clustered bellflower, geranium and Siberian iris for a bit of colour. Grasses like Korean feather reed grass and tufted hair grass can also tolerate these conditions. If your rain garden is big enough, you could also plant shrubs like dogwood or hydrangea.
A rain garden is the perfect way to filter and dispose of rainwater, helping the environment and keeping your home safe and dry in the process. By following these easy tips, you’ll have your rain garden planted and ready in no time!