How to Build a Rain Garden: 6 Steps

Rain garden under construction

If repeated rains have turned your lawn into patches of puddles or miniature wading pools, a rain garden could be the answer.

Also called a bioretention area or stormwater garden, a rain garden is a landscaped area that catches and filters stormwater runoff from impervious surfaces such as driveways, parking lots and patios.

The landscape feature creates a spot for water to pool, preventing it from going down the drain. Capturing surface area water and filtering it (rather than sending it through the stormwater system) helps improve water quality in several ways.

What a Rain Garden Does

Rain gardens:

  • Provide environmental protection for local waterways from toxins such as fertilizer, pesticides and motor oil.
  • Give habitat to valuable pollinator habitat.
  • Alleviate flooding and drainage issue.
  • Add a layer of stormwater management that protects local aquifers from overflowing.

“A rain garden solves a landscape problem,” explains Paula Gross, adjunct professor of horticulture at Central Piedmont Community College. “It’s not just pretty, it is part of an ecosystem that can have a positive impact on the environment.”

How to Build a Rain Garden in 6 Steps

Follow these six steps to establish a rain garden in your landscape:

1. Select a location

The ideal spot to build a rain garden is close to the house — but not too close — where it can capture water running off the roof. Gross suggests choosing a spot at least 10 feet from the foundation to avoid saturated soil from threatening the structure.

You can also choose a spot farther afield and direct downspouts toward the garden but avoid sunken spots where water pools (which means that infiltration is slow). Rain gardens should absorb water quickly; if you choose an area where it takes too long for water to dissipate, a rain garden will be less effective.  Avoid underground utilities and septic systems.

The size of the garden is up to you, but the Wisconsin Department of Natural Resources estimates that a typical residential rain garden runs 100-300 square feet. Anything smaller and you can’t fit in many plant varieties; anything too big requires a lot of time to tend.

Pick a spot with at least partial, and preferably full sun.

2. Prepare the site

Frankie Barker with the Mat-Su Borough walks the perimeter of the large in-progress rain garden installation at Palmer Senior Center in south-central Alaska. Credit: USFWS/Katrina Mueller

Outline the rain garden area, remove all of the grass and dig out the area until the center is the lowest point and the sides form a gentle slope toward the middle. The berm around the perimeter creates walls that will hold the water in when it rains. A well-designed rain garden can filter up to 1 inch of rainfall in four hours, according to the American Society of Landscape Architects. To help prevent erosion, surround the edges of the rain garden with landscape rocks.

Garden depth is generally 4-8 inches.

3. Direct Downspouts

Rather than letting water run from the roof, into the downspouts and across the driveway into the storm drain, redirect downspouts toward the rain garden. “You want to purposely direct rainwater into the garden, not just have it capture the rain that falls,” Gross says.

Dig a shallow trench that runs from the downspout to the rain garden; attach a rigid plumbing pipe to the downspout and cover with soil.

4. Pick the Right Plants

A good rain garden design captures rainwater so your plant selection must include species that can withstand deluge and drought. Native plants and wildflowers have evolved to adapt to these alternating wet and dry conditions. Gross recommends a plant list that includes perennials such as black-eyed Susan, cardinal flower and asters.

Your rain garden plants can include grasses and sedges, too. These “marginal” plants — so-called because they grow near the edge (or margins) of a pond in wetlands — include horsetail, sweetflag, bushy beard and swamp milkweed. All are well-suited to moisture extremes. The landscape designs that incorporate sedges and grasses tend to look a little unkempt and less formal, Gross adds.

Soil type will have a big impact on which rain garden plants you choose. Soil conditions determine how quickly percolation takes place. Sandy soils drain more quickly than clayey soils.

5. Maximize Mulch

A layer of organic mulch covering the soil in your rain garden helps the soil retain moisture and prevents weeds from sprouting up in the rain garden. Aim for at least two to three inches of mulch (and choose shredded hardwood mulch that has not been dyed). As the rain garden is established, check the depth of the mulch and add more as needed.

6. Maintain

A rain garden, like other landscape features, requires maintenance to thrive. Look for areas where the garden overflows when it rains. Adding more rocks or soil will keep the water in the garden. Do regular weeding and prune and replace plants as needed. You might need to water the garden during the first year until the plants are established.

“You can’t think you’re going to plant it and walk away,” Gross says.

Local Support, Cost-Saving Incentives

A few cities offer grants or cost-share programs to encourage homeowners to establish rain gardens in their landscape. In Northfield, Minn., homeowners can apply to be reimbursed for 50% of the cost of their rain gardens, up to $250. Lincoln, Neb., offers homeowners a rebate of up to $2,000 for “rainscaping” projects, including rain gardens.

Even if your community does not offer rebates, it may have a pilot program and offer advice on local plants — and encouragement.

Cities with informational support include:

Jodi Helmer

Jodi Helmer

Jodi Helmer is a North Carolina-based journalist who writes about farming and the environment.