How to Build a Rain Garden

By Natalie Yerger

Installing a rain garden not only serves as your personal contribution to clean water efforts in the community, it creates a lush, low-maintenance area that can provide your property with many benefits, like reducing runoff and creating a habitat for birds and butterflies. In this guide, we’ll explain what a rain garden is, how to create one, which plants to consider, and how to maintain it in the first year and beyond.

What is a rain garden?

A rain garden is a shallow, man-made depression that’s strategically located to capture water runoff from driveways, streets, lawns, walkways, and gutters. Like a native forest, a rain garden leverages heavy rain to recharge the aquifer, filters toxic materials before they can pollute waterways, and supports wildlife habitats.

Once the bowl-like depression is constructed, the area is landscaped with deep-rooted native flowers, shrubs, mulch, rocks, and grasses that excel in deflecting rainfall by slowing it down before it reaches the ground, filtering pollutants, and holding water in the subsoil. When properly placed, the depressed basin will draw the flow of water from large storms, allowing the water-loving plants within it to act like a living sponge.

Rain gardens vs. bioswales

Rain gardens are often confused with bioswales, another landscaping feature used to slow and filter stormwater. Bioswales are designed to accommodate larger quantities of stormwater and, as such, are longer and wider than rain gardens. Their intent is not only to filter the water but to redirect it away from roads and parking lots, so they typically slope to a destination.

Rain gardens focus on the absorption of water from rooftops and walkways, are shallow, and are completely vegetated for maximum absorption. The construction of a bioswale is a larger undertaking, often requiring engineered soils, higher investment, and deeper basin creation, whereas a rain garden is usually a DIY project.

Rain gardens vs. traditional gardens

A rain garden also differs from a traditional garden. Traditional gardens are small pieces of land used to grow vegetables, fruit, herbs, or flowers and are planted for a number of reasons, from cultivating food to stress management and aesthetic pleasure. Rain gardens, while pleasing to the eye and a welcome invitation for wildlife, have a specific functional purpose: to absorb and purify rain water.

Benefits of a rain garden

Much of the land in urban areas is covered with concrete or asphalt, meaning that stormwater runoff will flow into rivers at an accelerated pace. It’s one of the reasons developed areas tend to experience flooding more quickly than rural areas.

According to the EPA, urban runoff is the leading source of water pollutants that causes water quality impairment. In the case of a heavy rain, a well-planned rain garden will soak up the water, preventing it from cascading quickly into storm drains and carrying pollutants, oil, debris, and garbage with it. 

Aiding in your community’s clean water efforts can have personal payoff, too. Some municipalities require homeowners to reduce stormwater runoff or pay higher storm sewer fees, so a rain garden is an easy way to avoid those fees. Other regions grant rebates from local water boards for installing a rain garden. It will also indirectly save you time and money on lawn care by taking the place of turf.

Additionally, it’s a common misconception that rain gardens are an open invitation for mosquitoes to breed. On the contrary, properly designed rain garden basins will remove standing water within 24 to 48 hours and are an excellent habitat for more welcome wildlife, like birds and butterflies.

How to build a rain garden

Installing a rain garden is a task that most homeowners can take on without professional help, but its construction is more complex than a traditional garden and requires some knowledge and resources. Typically, a rain garden can be completed over a couple of days if you have the tools and plants on hand. Here’s a step-by-step guide to building a rain garden:

1. Do your due diligence

Before beginning, you’ll want to check with your municipality regarding any regulations. You’ll also want to check in with your local utility company to ensure the area is free of lines and septic tanks.

2. Choose a location

Once you’re in the clear, choose a location for your rain garden. The area you select for the basin should be in a place that can collect as much runoff as possible but is five to 15 feet away from your home to prevent damage to the foundation. An ideal spot would be in partial shade and downhill from a downspout or paved area (use a level to predict the flow of water).

Some homeowners will lay river rock or run an underground PVC pipe to channel water from a downspout to the garden. Other considerations for location include existing tree roots, retaining walls, and the groundwater table. 

3. Perform an infiltration test

Prior to digging, perform a soil infiltration test on the selected area. If the infiltration is low, it won’t be an appropriate spot for the garden. The infiltration test can also inform the garden’s size, as the garden’s surface area should be based on the size of the drainage that will contribute to the garden. 

4. Plan size and depth

The size of your garden should be determined by the volume of water it will filter. To estimate, use this calculator from the Rain Garden Alliance.

5. Excavate

You’ll need a spade and wheelbarrow to dig. A good depth to aim for is 1836 inches with a 6-inch ponding area and 1230 inches of soil amendments. Make sure to hang on to the topsoil, as it can be amended and reused or spread elsewhere on your property. Fill the excavated garden area with 50% sand, 25% topsoil with low clay content, and 25% compost.

6. Pick your plants

When choosing plants, know that native plants are preferred because they require little maintenance and will offer the most benefits to wildlife. The center of the garden should include perennials and native plants that tolerate wet feet, like cattails and cannas. Around these, prioritize plants that tolerate occasional standing water, like day lilies and bugbanes. On the outer edges, place plants that prefer dry soil like rosemary and butter daisies.

7. Mulch

Pile stones and extra soil on the downhill side to act as a berm—this will help water pool to a depth of roughly six inches. Mulch with compost can be added to the edges of your garden, and a well-placed rock or two can help prevent water from washing out of the space.

Rain garden design tips

We recommend keeping the following in mind when designing your rain garden:

  • Raised berms around the perimeter of smaller rain gardens can help contain runoff from particularly large storms.
  • If you live in a wet climate, consider adding three inches or more of gravel beneath the soil to help conduct excessive water away.
  • Consider the effects of rain garden plantings on your home and the surrounding environment. You can shade the south side of your home with trees and shrubs in sunnier climates.
  • Local and state government agencies and universities sometimes offer assistance for installing rain gardens, so check with your municipal office prior to installation.

Additional plants to include in a rain garden

Rain gardens can be divided into three zones, including a wet zone with plants that are tolerant of up to six inches of water, a mesic or middle zone with plants tolerant of several inches of water for a short period of time, and a transition zone with plants tolerant of drier soil. 

The ideal trees, shrubs, and perennials for each area of the garden will vary depending on where you live, but plant selections are relatively standard. For example, aster, iris, sedum, coneflower, artemisia, and daylily are common rain garden choices.

While most plants with the right moisture requirements will do well, native plants are best. These varieties require the least amount of maintenance, are best for local wildlife, and have deep root systems. Your local nature center and state department of natural resources can serve as helpful guides.

As you’re planning, select plants that bloom at various points throughout the year for season-long color. For visual purposes, a variety of plants will work best, like grasses, sedges, and rushes as a backdrop for flowers.

Left Day lily

Right Cattails

Rain garden maintenance

The first year after installation, you’ll want to baby your garden. Try to mulch often with shredded hardwood rather than pine bark and wood chips, which can float away. Regularly weed to allow the plants to get established. Decorative rocks can prevent heavy rains from washing out young plants, and new plants should receive about an inch of fresh water weekly to encourage deep roots that are efficient at absorbing water.

Once your garden plants have taken root, maintenance is limited to some weeding and regular watering during dry spells.

Frequently asked questions

Does a rain garden form a pond?

No, the rain garden fills with several inches of water after a storm. This water will be slowly filtered into the ground rather than released quickly into a storm drain. A rain garden actually allows more water to soak into the ground and drain in under 48 hours.

Will a rain garden become a breeding ground for mosquitoes?

No, rain gardens are not mosquito breeding grounds. They typically drain in 24 hours, while mosquitoes require 710 days of standing water to lay and hatch eggs.

How much does it cost to build a rain garden?

According to the Rain Garden Alliance, the cost to install a rain garden can range from $35/square foot when installing on your own to $1015/square foot when professionally installed. Use this calculator to determine how much it will cost you to build your own rain garden.

How do rain gardens help the environment?

Impervious surfaces such as roofs, driveways, sidewalks, and roads prevent rain water from soaking into the ground. When this occurs, rain water becomes stormwater runoff, which picks up pollutants like pet waste, fertilizers, litter, oil, and gasoline, and sweeps them downstream into storm drains.

These drains then empty into nearby waterways untreated. Stormwater is the greatest threat to water quality, and rain gardens mimic the natural water cycle by soaking the water into the soil, recharging groundwater for uptake by plants, and filtering water to prevent pollution from flowing into local waterways.

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