What is a rain garden and how do you build one?

Rain gardens are attractive solutions to water problems, turning poor drainage or gutter runoff into a beautiful, low-maintenance garden display piece. They slow rainwater from running off your garden onto the street and sewers, and help reduce lawn bare spots and erosion from fast currents, all while keeping your garden watered.

Rain gardens also filter rainwater through the soil before it drains into storm sewers, making your local streams, ponds, and lakes cleaner. Even better, most rain gardens are low maintenance, don’t require watering, and encourage birds, butterflies, and pollinators to visit your garden. How to create a rain garden in your backyard.

What is a rain garden?

In their simplest form, rain gardens are flat, bowl-shaped spots or depressions in your yard planted with flowers, shrubs, or grasses that thrive in moist soil and during droughts. Rainwater collects in a rain garden during storms, and then gradually seeps into the ground a day or two after the rains have stopped—too fast for mosquitoes to lay eggs.

Most residential rain gardens are fairly compact, ranging from 60 square feet to 180 square feet. They can be of any shape, like a straight rectangular flower bed along a walkway, a circle of flowers in a low spot in a yard, or a crescent moon along a slope.

What all rain gardens have in common is that they are made of soil that drains well after a storm. If you are planning a rain garden for that low spot in your yard where there is always a puddle, you will need to spend time digging up the soil and changing it so the location will drain faster.

How do I create a rain garden?

Step 1: Identify a waterlogged area or low spot in your yard

Look for a spot in your yard that allows water to drain away from impervious surfaces that won’t absorb water, such as a patio. your roof, patio, deck, driveway, or sidewalk. Keep the rain garden at least 10 feet from the foundation of your home to prevent water from draining into your basement. You can use a gutter extension to channel water into your rain garden. Just make sure to clean your gutters regularly. Keep rain gardens away from septic systems and tall trees that could damage their roots.

Step 2: Test the soil and add additional nutrients as needed

For a rain garden, you want soil that will drain within a day or two after storms. To test your soil, dig a hole six inches deep and fill it with water. If the water drains in less than 24 hours, the soil is suitable for a rain garden. If it doesn’t drain within 24 hours, you may have clay soil and you need to modify it (add different materials) to make it drain.

The soil consists of a mixture of three types of particles: sand, silt or clay. Sand consists of the largest particles, clay the finest particles, and silt particles are in between. If your soil has a lot of clay or silt it can drain slowly, and if you turn it over wet it can become a hard, compact lump.

You may need to add garden sand and compost to ensure your rain garden drains. Never add sand alone to clay soil or you will end up with a mix like concrete. Instead, for new rain gardens in clay soil, try mixing amounts of 50% sand, 30% compost, and 20% existing soil to a depth of 6 inches.

Step 3: Now it’s time to add rain garden plants

The most important thing to remember is that rain garden plants need to be able to stand up to two days in standing water and periods of drought as the site they are planted in can completely drain between rain showers. Fortunately, a wide variety of native plants are adapted to these conditions and thrive with little attention.

Plant flowers and shrubs that thrive best in dry conditions around the edges of your rain garden, and water-loving plants in the center that stay wet the longest when your rain garden drains.

Below are some of the easiest rain garden plants to grow in American rain gardens with average garden soil, adapted to hardiness zones four through seven (areas where the minimum winter temperature is between -30°F and 10°F. For more plant options, see the Environmental Protection Agency list of aquatic plants by state.

Here are ideas for rain garden plants to control rainwater runoff depending on where you live

Rain garden plants for the dry zone

• anise hyssop (Agastache foeniculum): Butterfly milkweed (Ascelpias tuberosa) makes cheerful, bright yellow-orange flowers on 2-foot plants in mid-summer in zones three to eight, and provides food and flowers for monarch butterflies and nectar for hummingbirds. Pink Marsh Spurge (Asclepias incarnata) prefers wetter conditions; Plant it in the wet zone of your rain garden.

• coreopsis (Coreopsis tinctoria): Also known as tick seed, this plant with fluffy yellow flowers also comes in red, orange, white, or pink. It grows in hardiness zones five through nine, and individual cultivars can persist in zones two through 11.

• New England asters (Symphyotrichum novae-angliae): These rain garden plants bloom from late summer until frost on 3-foot to 4-foot stalks in zones three through nine in shades of purple, lilac, and pink. They are particularly well adapted to dry locations. New York American Aster (Symphyotrichum novae-belgica) is a related flower with larger flowers; The ‘Purple Dome’ cultivar grows in a mound shape fringed with purple-petaled flowers with orange centers.

Central zone rain garden plants

• Blue false indigo (Baptisia australis): This flower blooms to a 3-foot bush in early summer in zones 3 through 10. If purple isn’t your jam, go for white false indigo instead.

• Boltonia (Boltonia asteroids) Stars: These produce mounds of white daisy-like flowers on 3-foot stalks in mid-summer and can bloom until frost in zones four through nine. The pointed, grey-green leaves are a good foil for purple blooms like blue false indigo.

• Japanese Maples: These plants are grown for their colored, lacy leaves, not their flowers, and vary from 5 feet to 25 feet in height at maturity; Check the label carefully and plant by their final height, not the size they are today. For small sites, choose a dwarf variety like the deep red Pixie Dwarf. Most Japanese maples are hardy in zones five through eight.

Rain garden plants for the wet zone

• Blue flag iris (Iris versicolor): This blooms in late spring with large, showy purple flowers veined with yellow and white. Hardy in zones three through eight, Blue Flag Iris thrive in moist rain garden soil.

• elder (Sambucus nigra): Here grow small fragrant white flowers, then purple-black berries known for their medicinal value – and attractiveness to migratory birds. The “Black Lace” hybrid grows up to 6 feet to 8 feet tall in zones three through seven with dark, deeply dissected leaves and pink flowers; ‘Adams’ does well in zones three through eight and can grow up to 10 feet tall with common green foliage.

• royal ferns (Osmunda regales): Ferns like to keep their feet wet and grow happily in shade as well as sunny spots in zones three through 10. Expect a maximum height of 2 feet to 6 feet, depending on how much sun it gets.

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