A rain garden is a landscaped area that captures and holds stormwater, allowing it to infiltrate into the ground rather than to become harmful surface runoff. Functional gravel or perforated pipe features allow for an increase in water storage, and are hidden under a mixed layer of mulch, soil, sand and compost. For a most effective design use native and perennial vegetation such as grasses, rushes, sedges and shrubs.
- Place garden in low-lying areas where stormwater runoff can be easily directed, or depress the bed approximately 6 inches lower than surrounding land.
- Garden should be at least 4 metres away from buildings, wells, utilities, underground fixtures, and septic tanks.
- Do not situate the garden in an area where water already pools. Instead, capture the water in an area before it reaches this location.
- Ensure the land has sandy, gravelly or loamy soil with little clay content to ensure proper drainage of stormwater. Determine your soil type here.
- Avoid disrupting large tree roots by staying away from the area under the tree canopy.
- Make sure you have enough space for your garden.
- Choose a location that is level or with a slope lower than 12% to minimize stormwater outflow from the bed.
- The base of the rain garden should be at least 1 metre above the groundwater table.
Before beginning any major projects or alternations, make sure you are aware of the locations of any underground pipes, gas lines, or electrical wires and be sure to obtain any permits that may be necessary.
Mark the area where you wish to start digging. Follow the guidelines for depth of your rain garden based on the slope:
- >4% slope, build a 3 to 5 inch deep rain garden
- 5-7% slope, build a 6 to 7 inch deep rain garden
- 8-12% slope, build an 8 inch deep rain garden
Ensure that the base of your garden is level by taking soil from the uphill area of the garden and adding it to the downhill area. Then, heap soil around all the edges except the uphill edge – this is called a berm. A berm acts to help hold water in your garden.
Enhance Your Soil
Depending on your garden’s soil type, mix in the following soil amendments. For more details on improving your soil quality, check out the soil enhancements page.
- Sandy Soil: Your soil needs more nutrients for your garden to flourish. Add compost and other organics. Adding mulch will minimize water evaporation.
- Clayey Soil: Clayey soil tends to be compacted, so add organic material to break up these compacted sections and allow the soil to breathe.
Picking Your Plants
It’s time to get creative – there is no single way to plant a rain garden but here are some tips for picking your plants:
- Select plants that have a well-established root system.
- Native perennials, especially shrubs and bushes, may have a higher initial cost but only need to be purchased once. Native plants adapt to your property and last longer if tended to properly. Check out our list of native plants here.
- Ideal rain garden plants should perform well in both wet and dry periods. Avoid larger trees as the roots may absorb too much water and deprive other plants in the rain garden.
- You may want to conduct a percolation test to determine the best suited plants for the level of soil moisture.
Well-designed rain gardens require minimal maintenance. Gardens with native plants do not require fertilizer or pesticides, but can benefit from fresh compost every year. As the plants are establishing their roots, typically the first two years after planting, the garden will need periodic watering. After this time, upkeep simply involves weeding.