A rain garden is a garden that is specifically designed to take in rain, usually off of a rooftop or road. It is bowl-shaped, so that the water may stay within the garden for 24-48 hours before absorption into the ground. Sometimes the bottom of the garden is filled with stone, especially pea gravel and river stone. Low maintenance, hardy native plants with deep root systems are chosen to beautify and landscape the space. Rain gardens help to prevent and reduce flood risk, and clean and absorb the rain where it falls.
A rain garden is designed with an inlet, where the water flows into it (from a downspout off of a roof, for example). It also has an outlet, in case the garden needs to overflow. Stones are usually used to create the inlet and outlet. Sometimes the edges of the garden are raised (or bermed), in order to keep the water in the bottom of the bowl shape.
An example rain garden
Notice the bowl-shape of the garden, and the stone leading from the downspout into the middle of the garden. There is also an outlet leading away from the house in case the rain garden overflows and the water needs somewhere to go.
Rain gardens are different from regular gardens in that they have a specific function, which is to collect and absorb rain. Therefore, rain gardens are designed with this function in mind, so they are bowl shaped and have an inlet and outlet to direct water into and, if needed, out of the garden. Sometimes rain gardens also have stone in the bottom of the bowl, to slow down the water flowing in from the inlet.
The types of plants planted in a rain garden must also be designed based on the garden’s function, planted with drought tolerant native species that don’t mind sitting in water for moments of time. It is the deep root systems of native plants that helps a rain garden obtain optimal absorption.
Because of these functions, there are specific requirements when designing a rain garden. It should always be located at least 3 metres (10 feet) away from the foundation of any buildings. The rain garden size and depth are planned to maximize absorption of rain from a downspout or road. A rain garden is also a great landscaping option for a low-lying wet spot on a property.
No. Rain gardens are designed to hold water for up to 24-48 hours, as the water is absorbed into the ground and taken up by the plants’ roots. Mosquitoes need 7-10 days to complete their life cycle, so a rain garden is not suitable habitat to support them. By contract, rain gardens help support dragonflies and birds that eat mosquitoes.
In cities, storm water ponds, clogged eavestroughs, and other sources of standing water (e.g., tires, unmaintained bird baths, and unused wading pools) can allow for mosquito breeding, but rain gardens are not.
Rain gardens require some maintenance. When the plants are first installed, they require either regular rainfall or regular watering until they establish, usually within 2-3 years. Once their roots are established, the plants can survive both drought and rainy conditions.
Weeding will help to maintain the aesthetic of the rain garden, and re-mulching every 1-2 years will ensure that the garden stays healthy. Also, it is important to regularly check to make sure that the inlet and outlet and bottom of the rain garden are clear of debris.
Rain gardens come in many different shapes and sizes. They should be designed to collect and absorb any water that flows into them within a 24 hour period. The size and depth of the rain garden will depend on the size of the property, the soil type, and the amount of water that is expected to enter the garden from a downspout. A general rule is that a rain garden should be about ¼ the size of the surface area of the joining roof or driveway. Usually the deepest part of the rain garden is 30 cm (1 foot) below the outer edges of the garden. Sometimes berms are added along the sides, and then the garden doesn’t need to be as deep.
In the event of a large rain event that may exceed the capacity of a rain garden, each rain garden should have an outlet so water can safely overflow from the garden. Any water that is collected and absorbed by the garden following a rain event will help reduce flood risk and improve the quality of the water.
A rain barrel allows you to collect natural, soft rain water during periods of heavy rain. You can then use this water for your garden instead of water from our municipal supply. You enjoy healthier plants and gardens and, best of all, you are protecting the environment by conserving water. Plus you also save money on your water bill. Learn more by downloading our Rain Barrel Fact Sheet and watching the installation video below. Purchase your rain barrel via the online GreenUP Store here >
This map was created in 2016, in order to identify areas where water accumulates in the spring and fall, or during heavy rain storms. Feel free to add comments where water pools on your property or in your neighbourhood!
You can also add to the map where rain gardens could help reduce flood risk, or if you are planning on installing a rain garden on your property.