Rain Gardens: What They Are and Why They're So Important

A Beautiful Way to Help Protect Our Water

Overhead of a rain garden

DigiPub / Getty Images

Rain gardens are often misunderstood, with many misconceptions around what they are and why you would have one. Maybe you've heard rain gardens are important for the environment, or you've heard that they are little gardens that go in soggy areas in your yard.

It's true that rain gardens are eco-friendly, but there's so more to this great garden project that would make you want one in your own yard.

What Is a Rain Garden?

A rain garden is a landscaped, shallow depression that captures, filters storm water and recharges our water sources.

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

Installing rain gardens in our communities are essential for the health of our water. As our green spaces become overdeveloped, rain gardens will become vital for the environment. They play a huge role in guarding our waterways from runoff which allows nonpoint source pollutants to enter.

What Are Nonpoint Source Pollutants?

 Nonpoint source pollutants (NPS) are pollutants that are picked up and carried to waterways by runoff (water, melting snow) flowing above or through the ground. Examples of NPS include:

  • motor oil
  • gasoline
  • fertilizer
  • herbicides and pesticides
  • pet waste

Characteristics of a Rain Garden

A rain garden is your individual way to practice environmental stewardship. These specialized gardens all have some features that make them distinct from your typical flower bed. A rain garden should reduce runoff, so it should be placed in a location enabling the garden to collect water.

The plants used in a rain garden should all be native species. Native plants control erosion by stabilizing soils and increase the recharge rate of water. The importance of using native can be seen in the comparison between Big bluestem grass (Andropogon gerardii) and Kentucky bluegrass (Poa pratensis) roots. Blue big stem roots can reach down to 12 feet, whereas Kentucky bluegrass will reach down as far as only 1 ½ to 2 feet, allowing for far less water infiltration.

Finally, a rain garden should recharge groundwater. When installing a rain garden, you are not looking to create a pond; ideally, the garden should drain within 24 hours after a storm.   

How Does a Rain Garden Work?

The principle of how rain gardens work is pretty simple. You have seen water run downhill before and have seen a puddle on a lawn slowly disappear. A rain garden creates a channel to an artificial depression or serves as an artificial depression, where water will be 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. A simple test can be performed to check your site’s soil drainage before you start working. The native plants and soil will also filter any contaminants in the runoff before it enters the groundwater.

Tip

How to conduct a water absorption test:

  1. Dig a hole at your rain garden site, 12 inches deep and six inches wide.
  2. Fill the hole with water and then let it stand until it has all drained into the soil.
  3. Refill the hole so that there is water one inch from the top. Push a pencil into the side of the hole to show the starting water level. Check what time it is and measure how deep the water in the your hole is with a ruler.
  4. Measure how deep the water is with a ruler every hour for at least four hours. 
  5. Figure out how many inches of water drained per hour.  

Considerations Before Making a Rain Garden

Putting in a functional, aesthetically pleasing rain garden won’t require you to bring in a landscaper or environmental scientist. With the help of a few assistants (friends, family members, neighbors), you can finish the project over a weekend, but it will require some planning.

Budget

Expect to spend around five dollars a square foot on the project. Most of your budget will be spent on plant material. Shop at local nurseries specializing in natives or grow your own from seed to save money on plants. Look for local plant sales that offer native plants for sale, as many extension services offer spring plant sales that will offer plants perfect for rain gardens. By installing the rain garden yourself, you will save a good deal of money compared to paying someone to install it for you.

Site Selection

The most important thing when planning a rain garden is site selection. Putting your rain garden in a spot that gets no water or too much water defeats the purpose. You want to look around and pick a spot between two impervious surfaces, for instance, a roof, a lawn and, a street. Examine where the water runs off the roof and exits the lawn, and runs to the street. These pieces of information will give you the location of your rain garden and your inlet and outlet.

Planning

To design and layout your garden, you will need to determine its depth and size, estimate the runoff amount, and use the soil percolation test mentioned above. Placing plants need to be done specifically to allow for water uptake and optimum plant health.

On the very edge of the garden, plants will need to tolerate dry conditions. Plants installed along the slope should be plants that can thrive in conditions that are sometimes dry or wet. In the deepest section of the rain garden, known as the base, you can place plants that can handle wet soil for an extended time.

The last part of planning before putting shovel to earth, call for utility markouts to safely identify your utilities in the area before beginning a project. Make this call before you dig to prevent damage to property and injury to you and your loved ones. Markout the area of your garden with white landscapers spray paint before they arrive.

Warning

Any time you dig at a depth of a foot or more, you should call your utility companies to safely identify your utilities in the area before beginning a project. Colored flags and markouts will be placed to alert you of any danger.