What is a Rain Garden?

Rain Garden

Wild petunias, red-twig dogwood, and scrumptious elderberry –– a charming rain garden will accentuate your landscape and invite nature’s guests for an afternoon snack. But did you know a rain garden in your yard serves a useful purpose?

A rain garden intercepts and absorbs contaminated rainwater runoff from your rooftop, driveway, or lawn. If your yard typically has excessive runoff and heavy water flow after a storm, a rain garden may be just what your landscape needs to look good and do good.

What is a Rain Garden?

A rain garden is not a water garden, and it’s not a wetland either. Rain gardens are generally dry and are only wet for up to 48 hours after a significant rainfall.

A rain garden is a spread of native shrubs, grasses, and perennials planted in a shallow depression, typically at the bottom of a natural slope. A rain garden intercepts and absorbs rainwater runoff from roofs, downspouts, sump pump discharge, and lawns.

How a Rain Garden Works

A rain garden removes pollutants and sediments from stormwater runoff. According to the Groundwater Foundation, rain gardens can remove up to 90% of nutrients and chemicals and up to 80% of sediments from runoff. Rain gardens also may absorb up to 30% more water than a conventional lawn.

Rain gardens are designed to block the rainwater’s path of travel and soak up the runoff. This absorption helps limit erosion and prevent rainwater runoff from entering and polluting the waterways and storm drains.

What is the History of Rain Gardens?

Natural water retention areas have existed in the Earth’s ecosystems long before urbanization. Yet the role of these first rain gardens has decreased over time as urbanized developments have obstructed natural water flow and redirected runoff to waterways and storm drains.

Rain gardens for residential use originated in 1990 when developer Dick Brinker began building his subdivision in Prince George’s County, Maryland. His thought was to replace expensive engineered drainage and retention systems with rain gardens that mimicked the natural retention process.

With the help of Larry Coffman from the county’s Department of Environmental Resources, Brinker managed to install a rain garden in each home of his subdivision.

Why is Rainwater Runoff a Concern?

As rainwater passes along roofs, driveways, and lawns, it collects pollutants such as fertilizer, pesticides, oil, bacteria, and litter. The contaminated water then enters storm drains and flows into streams and ponds, damaging the water quality.

If these pollutants enter the waterways, they may block sunlight from reaching marine life at the water’s bottom. These pollutants also may encourage rapid algae growth, depleting the water’s oxygen levels, and suffocating other organisms.

Your rain garden can collect this rainwater runoff before it reaches the storm drains. The water percolates through the rain garden’s soil, which filters out the pollutants and replenishes the groundwater supply.

Where to Plant Your Rain Garden

Rain gardens are the most useful when they intercept the runoff from impervious surfaces and provide stormwater management. Plant them in an area where they’ll interrupt the runoff’s flow and have good soil percolation.

Avoid placing your rain garden near buildings, utility lines, and or sewer systems. Functional areas to plant your rain garden include a slope’s downward depression or running curbside along the street.

A rain garden is usually 4 to 8 inches deep. The stormwater runoff should spread evenly across the rain garden for optimal absorption.

What are impervious surfaces?

Impervious surfaces are paved or hardened surfaces, like roads, sidewalks, patios, or driveways, that don’t allow water to reach the soil.

The lack of water absorption can limit groundwater supply, which can be a problem for communities that rely on wells for their drinking water. A rain garden can help to increase the absorption of rainwater and replenish the groundwater.

Plants Perfect for a Rain Garden

Good plant selection can also turn your rain garden into a natural habitat that invites wildlife, such as butterflies, toads, and birds. The PennState Extension offers an extensive list of plants that thrive in rain gardens and create a natural habitat, including:

  • Asclepias incarnata (swamp milkweed)
  • Caltha palustris (marsh marigold)
  • Eupatorium perfoliatum (common boneset)
  • Iris versicolor (blue flag iris)
  • Aesculus pavia (red buckeye)
  • Hamamelis virginiana (witch hazel)
  • Ruellia humilis (wild petunia)

A rain garden can make an attractive addition to your yard, even when it’s busy collecting rain. Consider how various heights, sizes, and flower colors can add beauty and appeal to your rain garden.

Lower your rain garden maintenance requirements by growing wildflowers and native plants, including grasses, trees, shrubs, and perennials. The perfect rain garden plants should have deep roots to absorb water and tolerate both the wet conditions after rainfall and dry conditions when rain levels are low.

Take note if your rain garden’s location receives full sun or shade, as this will affect which plants will grow best. You’ll also want only to grow plants the United States Department of Agriculture (USDA) recommends for your Plant Hardiness Zone.

Best Rain Garden Soil Conditions

A rain garden requires a permeable soil type (like sandy soil) that allows the water to percolate easily. When you build a rain garden with your existing soil, keep in mind that clay may cause moisture and drainage problems.

An infiltration test can help you determine how fast water can move through your soil. Unless your soil is permeable and water percolates quickly, you’ll likely need to create a sandy soil mixture.

The University of Maine Cooperative Extension recommends creating a soil mix that is 50% to 60% sand with the remainder as native soil. If you want to enhance the initial plant growth, the Cooperative Extension suggests replacing 20% of the mix’s native soil with compost. This soil mixture will help increase drainage and ensure the functionality of your rain garden.

When to Call a Professional Landscaper

Call a professional landscaper near you if you need assistance with installation or planning your rain garden design. Choosing the best plants, finding the location, and getting the soil just right can be difficult. Hire a landscaping professional, and they’ll do the hard work for you, so you don’t have to lift a finger.

FAQ about Rain Gardens

1. How do I maintain a rain garden?

Your water garden likely will need plenty of water during the first two years of its growth, especially when rainfall is low. Fertilization is typically unnecessary since rain gardens are designed to absorb excess nutrients.

Consider laying down an organic mulch, such as shredded bark, in your rain garden to manage excess weeds. Your mulch will need routine replacement, but it will act as a sufficient ground cover and add nutrients to the soil as it decomposes.

After heavy rainfalls, inspect your rain garden to ensure the water flow or any potential litter didn’t damage any plants.

2. Do rain gardens attract mosquitoes?

A well-designed rain garden that has no standing water after 48 hours should not attract mosquitoes.

3. What are bioswales and bioretention?

Rain gardens with complex drainage systems and engineered soil layers, such as bioswales, are often referred to as bioretention or bioretention systems. Bioretention is the removal process of pollutants and sedimentation from stormwater runoff.

Like rain gardens, bioswales are made up of native plants to help absorb water, prevent erosion, and absorb and filter runoff pollution. Yet bioswales capture a larger amount of water coming from greater impervious areas, such as parking lots and streets. Their more complex design also contains layers of soil and gravel, perforated pipe underdrains, and structural features that manage overflow from big storms.

Main image credit: James Steakley, CC BY-SA 4.0

Jane Purnell

Jane Purnell

Jane Purnell is an artist, writer, and nature lover. She enjoys teaching readers about the importance of eco-friendly lawn care, integrated pest management, biodiversity, and sustainable landscaping.