How To Design A Rain Garden

Photo credit – Rain Dog Designs, Gig Harbor, WA

What Is a Rain Garden?

A rain garden is, at its core, a garden that collects rainwater, holds it for a limited amount of time, and filters it before slowly releasing the water into the ground. It collects rainwater from impervious surfaces like roofs, pavements, driveways, patios, parking lots, or waterlogged yards, allowing the water to slowly seep back into the ground, preventing runoff from reaching local waterways.

Installing rain gardens in our communities can be essential for the health of our waterways.  As our green spaces become overdeveloped, rain gardens will become vital.  Read on to find out how to design a rain garden in your yard …

Benefits of a Rain Garden

These specialized gardens have features that make them distinct from your typical flower bed. The unique nature of a rain garden offers many advantages:

• A rain garden is your personal way to practice environmental stewardship.
• The primary purpose of a rain garden is to reduce runoff, so it should be placed in a location enabling the garden to collect water.
• A rain garden will provide food and shelter for pollinators, such as butterflies, and offer protection for songbirds and other wildlife.
• Rain gardens can control soil erosion.

Best Plants For Rain Gardens

Rain gardens can be placed just about anywhere—sun or shade—as long as you choose the appropriate plants. Rainwater generally soaks into the ground in 24 hours or so, depending on the intensity and frequency of the storms. With that in mind, know that rain gardens are not always moist. You need not use all native plants, but you should give consideration to the type of plants.

Create a rain garden as you would any other perennial border. Select plants based on their ornamental qualities—flower and foliage color, form, texture, and seasonal interest—and plant them in drifts or groupings. Choose plants that not only tolerate occasional flooding, but those that can also handle the hot, dry months of July through September in the Midwest.

Mesic-prairie plants such as big bluestem, black-eyed Susan, and compass plant are native plants that can tolerate wet soil for short periods. Mesic soils are considered “medium-moist soils” and comparable to average well-drained garden soil, while wet-mesic soils are medium moist to soggy most of the year.

Herbaceous native plants for rain gardens in sun include swamp milkweed, common tussock sedge, blue flag iris, wild bergamot, marsh blazing star, rosin weed, spiderwort, switch grass, Joe Pye weed, and cup plant. If an area in your garden is continually moist, you’ll want to choose plants that tolerate wet soil for long periods.

Select The Best Native Plants By State – Click Here To View

Rain Garden Drainage

• When installing a rain garden, you are not creating a pond; ideally, the garden should drain within 24 hours after a storm and able to collect and enter the ground slowly. 

• The rate at which water is absorbed is controlled by estimating the amount of runoff entering the rain garden. The amount of runoff determines the depth of the depression and the size of the rain garden. Absorption will be aided by adding native plants with deep root systems or amending the soil if it is not ideal. 

• Perform a simple water percolation test to determine your site’s soil drainage rate before you start working. (Watch the “how to” video below for tips)

How Does a Rain Garden Work?

• Rain gardens collect water from impervious surfaces such as rooftops, roads, sidewalks, compacted gravel, etc. The depression of the rain garden allows the collected water to infiltrate into the soil, which helps remove harmful pollutants and allows them a place to breakdown naturally.
• On the very edge of the garden, plants must be able to tolerate dry conditions. Plants installed along the slope should be able to thrive in conditions that are sometimes dry or wet. In the deepest section of the rain garden, known as the base, place plants that can handle wet soil for an extended time.

  

Where To Locate A Rain Garden?

• The most important consideration when planning a rain garden is site selection. Locating your rain garden in a spot that receives little to no water or too much water defeats its purpose.
• You want to choose a location between two impervious surfaces, for instance, a roof, a lawn, and a street. Examine where the rainwater pours off the roof via downspouts, watch how it flows to the lawn, and see how where the runoff water enters the street.
• Locate a rain garden at least 10 feet away from your home to avoid damaging the foundation. But it should go in an area where you can easily capture water from a roof, lawn, or a paved area.

In fact, properly constructed stormwater basins and rain gardens decrease mosquitoes in your community. Mosquitoes cannot breed successfully in wetlands, ponds or flowing streams, because either the water is moving, or there are predators to eat any mosquito larvae.

A rain garden is not a water garden. Nor is it a pond or a wetland. Conversely, a rain garden is dry most of the time. It typically holds water only during and following a rainfall event. Because rain gardens will drain within 12-48 hours, they prevent the breeding of mosquitoes.

What’s The Best Shape For A Rain Garden?

Ovals, kidneys, and teardrops often look best, but rain gardens can also be long and skinny. Use a garden hose to test possible shapes. Once you settle on a design, decide where the water will flow in and where any overflow will exit. Mark the shape with spray paint.

Quick facts:

A rain garden is a planted low area that allows rainwater runoff to soak in from hard surfaces like roofs, driveways, walkways and parking lots.

What Kind of Maintenance Does a Rain Garden Require?

When native plants are used, your rain garden will not require pesticides or fertilizer. As the rain garden is establishing during the first and second year or during periods of little to no rainfall, occasional watering of the plants may be necessary.

Rain gardens often require less care than other types of perennial beds. There is no need to buy bags of mulch, especially if the perennials are placed closer together when planting. As they fill out, they will help deter weeds. If you are planting a rain garden this fall, provide irrigation if the season is dry.

A helpful tool is a triangular hoe to remove weeds from between the plants the first season. Cut the perennials down in spring, leaving some stems standing 6 inches tall for tiny native bees that will lay their eggs in them. If the clippings are chopped fine, you can leave them as a mulch that will break down quickly.

Why Design A Rain Garden?

A rain garden filled with wildflowers and native plants adds more than beauty to your home. It’s an attractive and environmentally-friendly way to catch stormwater that runs off roofs, driveways and other surfaces. A rain garden also creates a welcome habitat for birds, butterflies and other creatures.