Rain gardens are a relatively new type of garden that combines the beauty of a well designed landscape with environmental and social wellbeing. Rain gardens are an increasingly popular choice for public green spaces, but are also great for gardeners who want attractive, low-maintenance gardens that benefit the wider community.
What is a Rain Garden?
A rain garden, also called a bioretention garden, is a landscape feature designed to collect and retain stormwater (rain and melted snow), preventing it from being lost to municipal storm drains. It usually consists of a depression for collecting water and a collection of plants that enjoy wet-dry cycles. It manages the water that runs off impermeable surfaces like roofs and driveways and reduces the watering needs of your soil.
Rain gardens vary in complexity depending on the scale and purpose. At the most basic level, they include a shallow depression in the ground, soil, some type of mulch, and plants. More complex rain gardens, usually designed to manage large quantities of water in public spaces, also include specialized bioretention soils, a layer of coarse gravel or stones, a system of pipes to take in and redirect water, and various structures that enhance the garden’s aesthetic. However, for the average sized home, a basic design is all that is needed and even simple ones benefit the environment.
Why Create a Rain Garden?
Many homes are constructed to direct stormwater off the roof and send it to the street where it enters the municipal storm system. Many driveways are impenetrable and also direct water to the street. This causes two environmental problems; the soil in your garden stays dry requiring more frequent watering and the municipality has added costs to collect and clean the water. A much better approach is to keep the water on your property. Plants grow better with less watering and city costs are reduced. A rain garden can do this for you.
Bioretention gardens also trap pollutants and eroded soils that wash off roofs and paved areas which would otherwise enter streams and lakes. Rain gardens help keep soil and water onsite which is beneficial for the long term health of your local watershed and groundwater supply.
Rain gardens are also a great option for urban wildlife enthusiasts. Depending on the plants, you can attract birds, butterflies, bees, frogs, or turtles. Unlike most other types of landscapes, bioretention areas allow rainwater to pool for a short period of time. These unique conditions attract all sorts of creatures. But don’t worry about mosquitoes – they need a couple weeks of standing water to breed.
Lastly, many municipalities offer generous rebates or incentives for residents who chose to install rain gardens, which is a nice bonus on top of the feel-good reasons for doing it.
Rain Garden Design
You might be wondering about the aesthetic look of a rain garden. The good news is that rain gardens can look like any other garden because it is the plants that are most visible and you have full control over their selection.
For the most eco-friendly approach you can choose hardy, native plants that need little care. Placing the plants close together, in irregular patterns, further enhances the “natural” appearance of your garden. You could also try selecting plants that are beneficial to wildlife, such as pollinator-friendly perennials or shrubs that produce berries for birds.
Most garden styles can be used. Japanese Zen gardens use a lot of gravel and rock and could be a great option for a soothing, low-maintenance rain garden. You could nestle Japanese ferns, grasses, moss, and irises between rocks around the garden. Other styles of rock gardens would work as well.
Do you love French formal gardens? Then you could try to recreate a parterre with a geometric bed using gravel and evergreen shrubs like boxwood (Buxus) and Lavendula (lavender). If you prefer cottage style gardens try planting an English perennial garden bed brimming with color. Basically, any gardening style works if you match your plant selection to the conditions of your garden.
Adding seating, shelter, walkways, and ephemeral water features makes the rain garden an interactive feature in the garden. Imagine looking forward to rainy days!
The Best Plants for Rain Gardens
What happens to water in a rain garden? When it rains, it collects in the garden creating a flooded condition. Over time the water seeps into the soil under and around the rain garden. If it does not rain for a while, the garden can get quite dry. Keep these different moisture conditions in the back of your mind when selecting plants.
The simplest way to choose plants for a rain garden is to pick native plants that are already adapted to alternating wet-dry conditions, or at least known to thrive in your gardening zone.
Rain gardens aren’t uniformly wet or dry, however. The most important feature of a bioretention area is the bowl-shaped depression – the behavior of water in this bowl creates different planting zones. You don’t need to follow these zones precisely, but they can help if you’re stumped on how to organize the plants.
The lowest point of the depression is the ponding zone and it is the wettest area. This area will remain relatively wet even when it’s not raining. Anything planted here will need to be tolerant of high levels of moisture and even short-term flooding. Select plants that love moisture such as Iris, Asclepias incarnata (swamp milkweed), Hibiscus moscheutos (swamp mallow) and Eutrochium purpureum (Joe Pye weed). Even some grasses, like Juncus (rushes) and Carex (sedges), do well in wet areas as do some ferns.
The next planting zone is on the slopes of the basin (#2 in the diagram). The slopes will be less moist than the ponding area because the water will drain towards the ponding area. This is an easy spot to plant because most plants enjoy moist but well-drained soils. It’s a good idea to use plants with deep or robust roots to hold the soil in place, such as Hemerocallis (daylily) and various grasses. For more color you can add lots of different perennials like Rudbeckia, Echinacea (coneflowers), Amsonia (blue star), Baptisia (false indigo) and more.
The final planting zone is the upland area (#3 in the diagram) which is the driest and suitable for Panicum (switchgrasses) and Schizachyrium scoparium (little blue stem). Sometimes a berm is created on the upland area to prevent water from overflowing from the garden during a storm event. You can plant any perennials or shrubs that prefer a drier well-drained soil here.
Of course, the examples listed are just suggestions. Planting choices can be very different depending on the theme you choose or your overall goals for the garden.
Creating Your Own Rain Garden
After this introduction to rain gardens you might be thinking of the possibilities for your own garden. Here is the next post in the series Building a Rain Garden – A Step-by-Step Guide.
Written by: Marika Li