How to create a rain garden

Recently, there’s been an increased focus on water quality in Ohio that’s forced state leaders and landowners alike to consider new avenues. While legislators are pondering stricter regulations, individuals should be evaluating their management practices to reduce their impact on the environment.

The Nutrient Mass Balance Study may have cited agriculture as a major contributor to the nutrient loading problem in Ohio’s waterways, but it isn’t the only contributor. In a typical house during a rainstorm, which we’ve seen plenty of this spring, water travels out of downspouts, across lawns treated with fertilizers and pesticides, into an oily street and down into a storm drain.

So that’s that. The water went into a storm drain, carried all those pollutants with it and it’s not your problem anymore.

Wrong. That storm drain empties into a nearby stream, river or bay.

So what can you do to make a difference? Install a rain garden.

What are rain gardens?

A rain garden is a designated area in your landscape that collects rainwater and soaks it up, reducing runoff. Grasses and flowering perennials are usually planted in a depressed area, so that rainwater from your roof, driveway or even the street can be collected and soaked up. Rain gardens can also filter out the pollutants in runoff and provide food and shelter for wildlife.

How to create a rain garden

1. Choose the right location. Avoid locations within 10 feet of your house, within 50 feet of your septic system, on slopes greater than 15 percent and near any underground utilities. Once you’ve selected a site you can test the soil’s percolation rate by digging a hole two feet deep and timing how long it takes for 8 to 12 inches of water to disappear. For example, if 8 inches of water drains in 12 hours, the rate is 8 inches divided by 12 hours or 0.67 inches per hour.  If your rate is higher than 0.5, your rain garden only needs to be 18 inches deep. If it is lower than 0.5, your rain garden should be 30 inches deep. Locations with a rate less than 0.1 aren’t suitable for rain gardens.
2. Determine the size and shape of your rain garden. The size of your rain garden will depend on your goals and the typical amount of rainfall in your region. If you want to build a rain garden that has the ability to handle most of your gutter water, you should contact your local extension office to help you determine what size suits the rainfall patterns in your area. If you don’t have enough space to collect all of your gutter water, that’s ok too. A small rain garden can still help reduce runoff. Rain gardens work well in oval, kidney and teardrop shapes.
3. Dig. After you’ve chosen a shape, marked the border of your rain garden and removed any grass from its surface, dig to the depth you need making an evenly, flat bottom so the water will drain evenly. If your rain garden is located on a slope, you’ll want to use some of the soil you dug up to create a berm on the low side of the slope.You want to make the base of the berm at least 2 feet wide, the top at least 1 foot wide and make sure the peak is 6 inches higher than water level when the garden is full.
4. Establish the drainage pipe. Once you have your rain garden dug out, you want to dig a trench for the pipe that will carry rainwater from your gutters to the rain garden. You can either install more durable rigid piping with smooth walls or non-perforated corrugated tubing. Just make sure the piping extends into the rain garden by a foot or so.
5. Fill in your rain garden. After you’ve installed your pipe you want to line the bottom of your trench with stones to prevent erosion. You may also place stones over and beside the pipe to hide it. Then fill in the rest of the trench with the soil you previously removed. For the rain garden, you want to fill in completely until the soil level is about 6 to 12 inches from the top. A good mix for rain garden soil is 65 percent native soil and 35 percent compost. If you dug out clay soil, refill with a mixture of 60 percent screened sand and 40 percent compost.
6. Add plants. Your rain garden is going to be set up in three zones. The innermost zone — zone 1 — will include plants that thrive in the wettest environment. The ring around zone 1 — zone 2 — will contain plants that can handle standing water. The outermost ring — zone 3 — will contain plants suited to drier environments. See the list below for suggestions from Penn State University on what to plant in each zone of a rain garden located in the Mid-Atlantic and Midwestern regions of the United States.
7. Mulch. Once your plants are in place you want to cover the inside of your rain garden with a 3-inch layer of mulch to keep the soil moist. You’ll have to check the depth annually and replenish as needed.
8. Water. Until your plants are established, you’ll have to provide supplemental watering to help your rain garden survive dry seasons.

Choosing plants for your rain garden

Zone 1 — the deepest area in the center of your rain garden. It will hold the most water for the longest period of time. Plants chosen for this zone should be able to tolerate standing water for a period of time. Penn State Extension extension recommends the following plants for zone 1 of rain gardens located in the Mid-Atlantic and Midwestern regions of the United States.

Shrubs

• Black chokeberry*
• Buttonbush*
• Elderberry*
• Ninebark 
• Possumhaw* 
• St. Johnswort*
• Silky dogwood* 
• Smooth alder* 
• Spicebush* 
• Swamp azalea 
• Swamp rose
• Wild raisin* 
• Winterberry*

Perennials and ferns

• Blue flag iris
• Blue vervain*
• Boneset*
• Cardinal flower*
• Cinnamon fern*
• Golden ragwort*
• Goldenrod*
• Great blue lobelia*
• Green bullrush
• Horsetail
• Marsh marigold*
• Monkey flower
• New England aster*
• New York aster
• Royal fern
• Seedbox
• Sensitive fern*
• Sneezeweed*
• Soft rush*
• Swamp milkweed*
• Swamp rose mallow
• Swamp sunflower*
• Switchgrass*
• Tussock sedge
• White turtlehead*
• Woolgrass*

Trees

• Bald cypress*
• Birch*
• Black gum*
• Black willow*
• Hemlock*
• Pin oak
• Pond pine*
• Red maple
• Swamp oak
• Sweet gum*
• Sycamore*

Note: Species noted with an asterisk (*) are also typically suitable for Zone 2 of the rain garden.

Zone 2 — the second ring in your rain garden. It will hold water, but drain much quicker than zone 1. Penn State Extension extension recommends the following plants for zone 2 of rain gardens located in the Mid-Atlantic and Midwestern regions of the United States, in addition to the plants listed in zone 1 that are marked with an asterisk.

Shrubs

• American beautyberry
• Broad-leaved meadowsweet
• Inkberry
• Narrow-leaved meadowsweet
• Red-osier dogwood
• Sweet pepperbush
• Virginia sweetspire

Perennials

• Blue false indigo 
• Blue star
• Boltonia
• Bottlebrush grass
• Broomsedge
• Culvers root
• Mistflower
• Obedient plant
• Threadleaf coreopsis

Trees

• Fringetree
• Ninebark
• Paw paw
• Red maple
• Serviceberry

Zone 3 — the upper or transition zone between the rain garden and the non-garden area. It will receive water during very heavy rain events and will drain the fastest. Almost any typical native plant will work in this zone. Penn State Extension extension recommends the following plants for zone 3 of rain gardens located in the Mid-Atlantic and Midwestern regions of the United States.

Shrubs

• American cranberry bush
• Black chokeberry
• Bush cinquefoil
• Fragrant sumac
• Gray Dogwood
• New Jersey tea
• St. Johnswort
• Sweet pepperbush
• Virginia sweetspire
• Witch hazel
• Yellow root

Perennials

• Anise hyssop
• Blazing star
• Blue star
• Boltonia
• Butterfly weed
• Calico aster
• Evening primrose
• Golden aster
• Green and gold
• Mistflower
• Threadleaf coreopsis
• Tickseed

Trees

• Buckeye
• Carolina silverbell
• Staghorn sumac

Resources

• Penn State University
• United States Environmental Protection Agency
• This Old House