What Is a Rain Garden and How Do You Make One?

What Is a Rain Garden and How Do You Make One?
Photo: Peter Turner Photography, Shutterstock
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Rain gardens one of those rare examples of something that is useful, sustainable, cost effective and also beautiful. If you’re not familiar with the concept of rain gardens, they might look like a small (in some cases), randomly placed garden in someone’s yard, but it’s actually the opposite. Rain gardens require planning, precision, and yes, a little maths. Here’s what to know about rain gardens, including what they are, and how to make one.

What is a rain garden?

First things first: a rain garden is a garden where native shrubs, perennials and flowers are planted in a small dip in the ground, usually formed on a natural slope, the Groundwater Foundation explains. The goal of a rain garden is to temporarily hold and absorb rain water runoff coming from roofs, driveways, patios or lawns. Sounds good, but do they work? We’ll let the Groundwater Foundation break it down:

Rain gardens are effective in removing up to 90% of nutrients and chemicals and up to 80% of sediments from the rainwater runoff. Compared to a conventional lawn, rain gardens allow for 30% more water to soak into the ground.

Keep in mind that a rain garden is not a water garden, pond or a wetland. In fact, it’s dry most of the time, with the exception of during and within 12-48 of a rainfall, the Groundwater Foundation explains. And so, unlike areas of stagnant water, rain gardens do not give mosquitoes a place to breed.

Great, but how does planting a garden in an indentation in your yard make a difference? According to Jeanne Huber at This Old House:

Rain gardens allow water to pool during a downpour, then slowly percolate into the soil. The shallow catch basin is a flower-bed destination for water rather than a travel route, like a swale. A fast-draining soil mix encourages water to sink in and promotes lush plant growth. Runoff may flow into a rain garden from a swale or pipe, or may simply run in from a sloping yard.

How to make a rain garden

Before you start digging, find a spot at least three metres from your house, and at least 12 metres away from a septic system or steep slope. While there are several steps involved with setting up a rain garden, the project should take between three and four hours. Here’s exactly what you need to do, per Huber at This Old House:

  1. Before digging, call the utility locating service to mark any underground pipes and wires.
  2. Use marking paint to draw borders for the rain garden.
  3. Scrape off any existing grass and roots in the garden location using a shovel.
  4. Dig down 18” using shovels and discard the removed soil. A pick axe may be used to break up heavier soil.
  5. Add 1-2” of coarse sand to the hole and spread it evenly with a metal rake.
  6. Remove the plants from their nursery pots and stage in place.
  7. Use a hand claw to tease the roots and encourage outward growth.
  8. Backfill the hole using a soil mix that is 1/3 coarse sand, 1/3 compost, and 1/3 bark mulch.
  9. Water the plants thoroughly, then cover in a layer of bark mulch.
  10. Continue to water for a month until the plants are established and then the plants should survive on only rain water.

And what should you plant in a rain garden? Huber recommends planting species that tolerate wet conditions — native sedges and lady fern — in the centre of the garden, surrounded by plants that can handle occasional standing water, like red twig dogwood. On the outer perimeter of the garden, opt for plants that prefer ­drier soil, like native evergreen and deciduous shrubs.

For more information on all-things rain garden, this page on the U.S. Environmental Protection Agency’s website likely has what you need.

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