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What Is A Rain Garden And How Do I Build One?

Rachel Burris7-Minute Read
August 19, 2020

The sound of rain falling on your rooftop, driveway and road may be pleasant to hear. But, that soothing sound is a symptom of a larger problem. These nonporous surfaces create stormwater runoff, as they prevent water from being absorbed into the soil. Stormwater runoff may not sound like such a bad thing, but as it accumulates, it can damage your property and have dangerous effects on the environment.

If you’ve noticed a large amount of stormwater runoff, it may be time to do something about it. Depending on the landscape of your property, creating a rain garden may be just the thing to keep your stormwater runoff in check. Before we get into how to grow a rain garden, let’s go over what a rain garden is and examine the problems with stormwater runoff, so you have a better idea of why you should create one. After reading this article, you’ll be able to do your part to help the environment and protect your home in the process.

What Is A Rain Garden?

Rain gardens are an environmentally friendly solution to stormwater runoff problems. Planted on downward-sloping ground, they use native plants to catch, hold and filter runoff. By creating these gardens, homeowners are able to minimize stormwater runoff, eliminate issues with water drainage and prevent pollutants from entering local bodies of water.

What Is Stormwater Runoff?

Stormwater runoff is rainwater that’s unable to be absorbed into the ground. As the rainwater flows off nonporous surfaces, like paved roads, driveways, patios and rooftops, and across flat ground, it collects a number of pollutants, like nitrogen, phosphorous, metals, oil, gas and pesticides. Instead of being soaked up by the soil or evaporated into the air, as is the case in forests, the massive amount of water eventually flows into local bodies of water.

Why Is Stormwater Runoff A Problem For Homeowners?

When it rains or snows, you may notice that your gutters overflow, your yard remains soggy or water pools in certain areas. These problems are often the result of stormwater runoff. When it’s left unmanaged, it can cause serious damage to your home, like a flooded basement, leaky roof, or cracked foundation. It can also lead mold and mildew to grow, septic systems to flood and water wells to become contaminated. Dealing with water damage can be time-consuming and costly, which is why it’s best to get ahead of the problem whenever possible. 

Is Stormwater Runoff Bad For The Environment?

As more and more land has been developed, stormwater runoff has become a growing environmental concern. With the increasing amount of construction of both properties and paved roads, there is less soil for stormwater runoff to be absorbed into. When the water isn’t soaked up into the ground, it flows to local bodies of water, where it causes floods and erosion that disturb natural habitats.

Stormwater runoff is also referred to as polluted runoff because of the fact that it picks up a large number of pollutants and carries them into waterways. As the water collects sediment and heavy metals from building sites, oil, grease and toxins from automobiles, fertilizers and pesticides from yards and bacteria and viruses from septic systems, it travels through storm drains and is deposited into streams and rivers. The polluted water decimates wildlife populations and destroys local vegetation. Furthermore, it can also find its way into local sources of drinking water, making it dangerous to consume.

Now let’s get into the details about how rain gardens help with stormwater runoff and what you can do to create one on your property.

Can A Rain Garden Solve Problems Caused By Stormwater Runoff?

To prevent costly damages to property and protect the environment, many homeowners are now building rain gardens. These gardens collect stormwater runoff and filter it through the soil before it has a chance to reach storm drains. Let’s go through how rain gardens work.

As stormwater runoff accumulates, it creates pools of water. Since rain gardens are built on sloped land, they prevent the water from traveling to the storm drain and instead allow the water to collect in the sunken planted area of the garden. By trapping the water in the depressed area, the runoff is given the time it needs to be fully absorbed into the soil. The absorption process usually takes about 12 – 48 hours.

Thanks to the vegetation planted in the depressed area, bioretention is able to take place. Bioretention is the process by which soil and plants filter out the pollutants within water. As the roots hold the water, the pollutants contained in the runoff are percolated through the soil. The sediment is retained by the stems, while the nitrogen and phosphorus are absorbed, enhancing the plants’ growth. The deeper the roots of the plants, the better the water is absorbed.

Where Should I Plant A Rain Garden?

You can minimize the amount of stormwater runoff on your property by building your own rain garden. If you live on a modest plot of land, don’t worry: Even very small rain gardens can make a difference.

To determine the best place to build your rain garden, observe how water travels across your property. Ideally, it’s best to choose a spot that’s sloped below your house and just above where runoff accumulates.

However, it’s crucial that your rain garden is neither on top of your septic system nor less than 10 feet away from your house. If your rain garden is built too close to your foundation, it could cause flooding. Since creating your rain garden will require digging, you also want to ensure that you don’t place it above utility lines or under trees. If necessary, it’s possible to run a pipe through the area that directs the runoff to the garden.

Planning A Rain Garden

Although creating a rain garden necessitates more planning than your typical garden, it requires minimal maintenance once it’s fully set up. Let’s take a look at the five necessary steps for planning and establishing your rain garden.

1. Consider Your Plants

Before you begin building your rain garden, it’s important that you determine what you’ll be planting in it. Rain gardens typically have three different zones that each incorporate plants with different levels of water tolerance.

The first zone in the center of your rain garden is where most of the water will pool, so you’ll want to use plants that can withstand standing water. Native plants are recommended for this area because they have deeper roots that can absorb more water.

The second zone wraps around the perimeter of the first. This area should be filled with plants that can endure intermittent periods of standing water.

The third zone, which is the outermost ring or edge of the garden, should include plants that are drought-tolerant. Plants that are accustomed to drier climates are preferable in this zone because they’ll receive the least amount of water.

Speak to someone at a local gardening store to find out which plants are native to your area and how each species tolerates water.

2. Test Your Soil

After determining the location of your rain garden, you must test the soil to ensure that it can infiltrate the water fast enough. The ideal rate is of infiltration is .5 inches per hour or higher. To test the rate of your soil, dig a 2-foot deep hole in the desired area, time how long it takes for 8 – 12 inches of water to be absorbed and divide the amount of water by the number of hours.

For instance, if 10 inches of water is absorbed in 16 hours, the infiltration rate would be .63 inches per hour. If your rate is below .5 inches per hour, you’ll have to dig a deeper hole. If your rate is below .1 inches per hour, you’ll have to find a better site for your rain garden.

3. Cut Your Grass And Begin Digging 

Once you’ve decided on the size and shape of your rain garden, mark the perimeter and remove the grass within the area. It’s best to do this with a sod cutter, so you can sever the roots and roll large sections of the grass off the area. Then, it’s time to start digging.

Most rain gardens range from 4 – 8 inches deep and consist of 100 – 300 square feet. As you dig, make sure to create a flat base in the center of the garden that’s at least 2 feet wide to ensure that the water can infiltrate uniformly. You’ll want the sides of the garden to be sloped so that it's shaped like a bowl. Just make sure the outer edge of the garden is high enough to keep the water from flowing out – shoot for at least 6 inches above the highest expected water level. 

4. Add Soil, Plants And Mulch

When adding soil to the area, leave about 6 – 12 inches empty. For regular soil, combine it with compost before refilling, so it’s 65% soil and 35% compost. For clay soil, fill the area with 60% sand and 40% compost.

When you begin planting, make sure that you put the native plants that can withstand the most water in the center. Then, move to the middle ring, and plant the second most water tolerant plants along the slope of the garden. The drought-tolerant plants should be reserved for the edge of the garden. After everything has been planted, you’ll want to add 3 inches of mulch across the entirety of your rain garden. 

5. Upkeep

As your plants begin to grow, you should water all of them, including the species in zone 3, which require the least amount of water. This additional watering will ensure that all of your plants live through the drier seasons.

Because you included compost in your soil, you will not need to fertilize your rain garden. However, you should add mulch on an annual basis to ensure that the mulch layer never gets below 3 inches. As time goes on, your rain garden will become mostly self-sufficient. Just be sure to weed and prune it regularly.

Summary: Good For Your Home, Good For The Planet

Stormwater runoff is detrimental not just to your home but also to our planet as a whole. If we want to eliminate pollution from our waterways, protect the wildlife in our communities and ensure the planet outlives us, we need to start taking measures to limit the amount of runoff that enters our storm drains. Creating a rain garden on your property is a fantastic way to start doing your part. Your rain garden will increase the amount of runoff that’s absorbed into the ground and add beauty to your yard.

If you think the rest of your land could use some sprucing, check out some other ideas for how you can elevate your landscaping.

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    Rachel Burris

    Rachel Burris is a writer covering topics of interest to present and future homeowners, as well as industry insiders. Prior to joining Rocket Companies, she worked as an English teacher for the New York City Department of Education and a licensed real estate agent for Brown Harris Stevens. She holds a bachelor's degree in creative writing from Bucknell University, a postbaccalaureate certificate in psychology from Columbia University and a master's degree in English education from Teachers College, Columbia University.