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Divert, Capture, and Filter Rainwater

    Divert, Capture, and Filter Rainwater

    Gardeners can face many challenges on their property—poor soil conditions, steep slopes, invasive plants, roots that produce juglone, insect and four-legged pest issues, among others. A rain garden addresses the challenge posed by heavy rainstorms, especially if they consistently leave a wet area on your property. The garden can also absorb the water from your rain barrel overflow and downspouts, and filter water before it reaches the sewer system. Not only is a rain garden a practical solution for a gardener, it also helps the environment at large.

    This article is going to dive into rain garden benefits, as well as how to go about planning for a typical residential rain garden. It will also offer some suggestions on what to plant.

    dry bed in a front yard
    A river rock swale was an integral part of the landscape design for this front yard. It diverts water away from the home’s foundation, but also serves as drainage. The surrounding garden features native plants. Photo by Mike Prong of Fern Ridge Eco Landscaping Inc.

    What is a rain garden?

    During every big rainfall, as water flows down driveways and sidewalks, and off rooftops, it washes everything it encounters in its path—chemicals, fertilizer, dirt, road salt—into storm drains, as well as into our lakes, rivers, and streams . A rain garden is a shallow depression or basin (referred to as a swale or bioswale), typically filled with native perennials and groundcovers, that holds and slowly filters some of that rainwater. It captures and holds rainwater runoff from patios, downspouts, pathways, and the downpour itself.

    When I was researching Gardening Your Front Yard, I liked the way certified fusion landscape professional Mike Prong described a swale. He liked it to digging a pool in the sand at the beach and then diverting the water along a channel to another pool.

    A rain garden can also feature a dry creek bed (also referred to as an arroyo) as part of the design. This also helps to divert and slow the water from a deluge.

    According to the Groundwater Foundation, a rain garden can remove up to 90 per cent of nutrients and chemicals, and up to 80 per cent of sediments from stormwater runoff, and allow for 30 per cent more water to soak into the ground than a traditional lawn .

    newly planted rain garden
    New green thumb Jessica Hachey requested a Catch-The-Rain consultation (offered through a non-profit organization called Green Venture). The contractor, AVESI Stormwater & Landscape Solutions, came to the house, reviewed the property and made recommendations, one of which was to create a rain garden in an area where there were issues with water leaking into the home. Plants were chosen to fit Hachey’s love of a woodland garden aesthetic, and more will be added this spring. Photo by Jessica Hachey

    rain garden benefits

    There are several benefits to having a rain garden on your property. I think the best one is knowing you’re doing your part to help your local environment. Also, there isn’t a lot of ongoing maintenance required once the rain garden has been built!

    Rain gardens:

    • Provide the water from your downspouts with a place to go (if they’re not diverted into a rain barrel). Or, manage the overflow of your rain barrel.
    • Remove impervious surfaces so that excess water has a place to go during heavy rain events.
    • Allow you to see where the water is going and make changes accordingly if there’s an issue.
    • Help to minimize flooding.
    • Manage consistently wet areas of your property.
    • Keep your basement and foundation of your house safe by diverting water away from it.
    • Filter rain into the ground to minimize water pollution from it being washed into sewers, creeks, streams, etc.
    • Attract beneficial insects and other important wildlife to your garden with the biodiversity you create via plant selection.
    • Prevent polluted rainwater from reaching streams, creeks, and other waterways.
    A rain garden after a storm
    The coolest thing about a rain garden is when you get to see it in action after a big rain event (as my weather app likes to call it). Photo by Elizabeth Wren

    It’s worth noting the intention is not for the garden to hold the water indefinitely like a pond. It’s meant to drain. I mention this because of concerns some may have about mosquito-borne illnesses, like the West Nile virus, and not leaving standing water on the property. It should take no more than 48 hours for the garden to drain.

    How to build a rain garden

    Before you plan to do any digging, move earth around, or change the grade of your property in any way, I would recommend consulting a professional and also making sure you know where any underground utilities are located (check with your municipality or utility companies to see if they offer a “call before you dig” program). Even if you want to do the bulk of the work, a professional can guide you with a drawing and some instruction, so you’re not inadvertently diverting water to a neighbor’s property or towards your home.

    A rain garden doesn’t have to take up a lot of space. It can be anywhere from 100 to 300 square feet and you’ll want to place it at least 10 feet away from the house. An infiltration test, which determines how fast the water drains through your soil, will alert you to any issues. It shouldn’t take longer than 48 hours to drain.

    The rain garden “dish” is generally amended with good-quality soil and compost, and sometimes sand. You want to make sure the soil is absorbent. After everything is planted, a layer of mulch helps with maintenance (especially during that first year) as plants fill in, by keeping weeds down, enriches the soil, and limits evaporation.

    Other elements that can help with properly capturing stormwater include permeable pavers for both pathways and driveways, as well as installing a rain barrel, so you can save the water for your garden (if it’s permissible in your area).

    a rain garden sign
    Rain gardens are often accompanied by a sign, either from the company that designed the garden, or the municipal program that helped spark the project. It’s a great way to share what you’ve done with your neighbors and those who happen by. Photo by Jessica Hachey

    what to plant

    When you’re making a list of rain garden plants, look for native plants. These options will have adapted to the conditions in your region. These will also attract beneficial insects and support wildlife, and are generally pretty low maintenance. Once plants become established, deep root systems help with the filtration process and work to absorb nutrients.

    a rain garden filled with native plants
    In this garden (also created through the aforementioned Green Venture program), the downspout was rerouted into a rain barrel. The overflow pipe runs along a rock swale that drains into the garden. Upturned sod was used to create a berm. The garden was then filled with triple mix soil and mulch. Plants include Doellingeria umbellata (flat-topped asters), Helianthus giganteus (giant sunflower), asclepias incarnata (swamp milkweed) Symphyotrichum puniceum (Purple-stemmed aster), Lobelia siphilitica (great blue lobelia) and Anemone canadensis (Canada anemone). Photo by Steve Hill

    You’ll want to consider plants for the parts of the rain garden that hold the most water. Keep in mind that different plants will be added to the sides, which tend to be drier. Look for double-duty plants that can tolerate heavy rains as well as drought, such as Pee Wee hydrangeas and Invincibelle Spirit smooth hydrangea, coneflowers, Phlox paniculatafountain grasses, globe thistle, etc.

    lobelia cardinalis
    Lobelia cardinalis (cardinal flower) in a rain garden. Photo by Steve Hill

    native plant resources

    US: Native Plant Finder

    Canada: CanPlant

    Other eco-minded articles and ideas

    rain garden tips and benefits

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