Rain Gardens: The Essential Guide

By Land8: Landscape Architects Network on August 28, 2014 No Comments / 6718 views

Rain Gardens: Embracing the Environment to Create Thoughtful Spaces. You probably know from our previous article “Permeable Paving: The Essential Guide” that it is possible to allow water to infiltrate paths and roads with the use of permeable paving. But have you ever heard of the possibility of imitating natural forest infiltration within your own garden?

What is a Rain Garden?

The rain garden, as its name suggests, is a group of planting arrangements that make use of rainwater. The rain garden is usually small and can be incorporated into pretty much any outdoor design. While rain gardens are most commonly found in residential yards, they can also be planted in parking lots and parks. They can even function by themselves as small independent gardens.

Balam Estate Rain Garden provide an effective stormwater management. Water from rain, passes through the rain garden, and the filtered water then flow into the stormwater drain. Credit: Rogersoh, CC 3.0

Balam Estate Rain Garden provide an effective stormwater management. Water from the rain, passes through the rain garden, and the filtered water then flow into the stormwater drain. Credit: Rogersoh, CC 3.0

What differentiates this planting design from others is that it includes a shallow constructed depression planted with deep-rooted plants and grasses. Why Would I Need to Have One? Rain gardens are vivid mélanges of plants of different colors and shapes. But their benefits are not merely aesthetical; they also provide ecological and economic advantages.

Rain gardens serve as an inexpensive method of reducing stormwater runoff volume and improving stormwater quality as they effectively absorb and reduce pollutants.
They function like the natural absorption of rainwater in a forest or meadow, often absorbing 30 percent to 40 percent more runoff than a typical garden lawn.
They endure the extreme moisture and concentration of nutrients such as nitrogen and phosphorus present in stormwater runoff.
These planting arrangements also contribute to facilitating the infiltration of clean water, therefore conserving it and recharging groundwater.
Birds and butterflies are provided with an ideal habitat, which in its turn reduces mosquitoes and pests.

What Sort of Plants Should Be Used? In order to attain the desired outcome, one must pay attention to selecting the appropriate plants. Rain gardens work as a balance of properly engineered soils, available space, a well-studied budget, and the right type of vegetation.

Swale and Rain Garden in Traffic Triangle, near Bartrams Garden. Credit: Philadelphia Water Department, CC 2.0

The kind of plants to be selected naturally depends on the climate of the area. There are, however, criteria that apply to all cases:

It is best if the plants used are native. A good investigation of the available local vegetation is thus needed. But native plants are not the only option, as other non-invasive species also can be planted.
Most rain gardens are generally planted with trees, woody shrubs, or herbaceous perennials. Annuals also can be an option.
When choosing the rain garden plants, the priority is not the seasonal aesthetics, color, or texture, but creating a garden that needs little maintenance.
The plants should be tolerant to drought and temporary ponding of rainwater. They must also naturally have deep roots and be able to survive the stress of heavy rainfall, pollutants, and nutrient excess.

RBC Rain Garden at the London Wetland Centre Nearly a year after it opened the Rain Garden (funded by the Royal Bank of Canada) is maturing well. In the photograph is one of the creature towers to provide habitats for insects and small mammals. They have been put together with a variety of materials from slates to sticks. Credit: CC 2.0 © Copyright Marathon

How Does a Rain Garden Work and How to Install it?

The rain garden serves its purpose by capturing rainwater from the roof or ground surfaces and allowing it to soak gradually into the ground. By doing so, the garden filters contaminants and conserves clean water, which would have been otherwise wasted in the sewer system or flooded in the streets.

Image credit: Tip of the Mitt Watershed Council.

In order to successfully build the rain garden, the first step is to find a suitable location. In residential areas, it is recommended that a rain garden be placed a minimum of three meters away from the house so that it doesn’t damage the foundation. It is also best if it is located in full or partial sun and distributed into smaller rain gardens, rather than having a single large one. In order for the rain garden to function well, it is important to ensure that it receives enough water during a rainstorm. For that, it should be located in a low spot; otherwise, measuring the drainage area is needed. Before digging the garden, the design must be well planned on paper first with the proper shape, boundaries, mulching material, and plants selected. WATCH: Rain Garden at Elk Grove

The next step would be, after checking the underground utilities, to remove any existing grass and dig about 10 to 20 centimeters deep, prepare a mix of soil and compost, and plant the garden as planned (a reservoir can be added to the ground for faster infiltration). Adding a layer of mulch to the rain garden is crucial for better erosion control and moisture maintenance. WATCH: An overview on building rain gardens

Learning about rain gardens has given me with one more reason to think that plants are the finest magicians of the environment we live in. So when designing a garden — or any open space –make sure to keep that in mind and make the best of their powers. Recommended Reading: