Nancy McQuillan’s rain garden was shown to green thumbs during last summer’s Naturally Beautiful Backyards Programs Earth-friendly Garden Tour. / Photo by Ruth Zschomler

You’ve heard of flower gardens and vegetable gardens, but have you heard of rain gardens? No, you don’t grow rain…that comes naturally in our part of the country. However, you do use the rain in a unique way. Instead of letting storm water run into storm drains, it is directed into a rain garden. The gardens store, filter, and slowly reintroduce the rain directly back into the depleting aquifers.

Just as rain barrels collect water for home use, keeping it from the storm drains, rain gardens also help mitigate the water cycle. Rain is meant to be absorbed back into the soil. With increasing amounts of impervious surfaces found in urban areas, more storm water is forced to bypass that stage of the water cycle. What we have always considered a renewable resource — fresh drinking water from the aquifers — is being depleted. Rain gardens help recharge the local groundwater supply.

Nancy McQuillan of Ridgefield is proud of the fact that all the water coming onto her 90’ by 100’ city lot stays on the property. Instead of sending the storm water runoff into the sewer system or waterways, she directs the water into two rain gardens through a series of gutters, downspouts and underground pipes. Her plants are thriving.

Why a rain garden?

Rain gardens help reduce flooding both on neighboring properties and in local streams. They filter chemical fertilizers and pesticides seeping from lawns into waterways. Oil and grease from driveways as well as other pollutants are filtered, too. According to the Department of ecology, storm water is the leading contributor to water quality pollution of urban waterways in Washington.

Rain gardens can also attract birds, butterflies, bees and other beneficial insects.

How to build a rain garden

Rain gardens, unlike vegetable and flower gardens, are not level or raised. Rather, they are usually dug out like a shallow pond and planted with appropriate plants:

1. Identify the best location on your property for your rain garden. It should be at least ten feet away from the basement or foundation and slightly downhill from the downspouts.

2. Test the soil for absorption rate. Water should drain out of a fully soaked and filled six-inch hole within 24 hours. If it doesn’t, look for another site in the yard.

3. Determine size and shape for your rain garden.

4. Excavate 18 to 30 inches of soil and work in compost. Level the bottom of the depression.

5. Create an entry to the rain garden for water. This can be a pipe, swale, or landscaped area. Provide a rock-lined overflow.

6. Select a variety of small trees, shrubs, herbs or grasses that have suitable water needs. Native plants and hardy cultivars are usually the best.

7. Mulch the exposed soil with two to three inches of mulch and water well. Continue to mulch as needed.
8. Do not use fertilizers or pesticides in the rain garden.

9. Keep inlet and outlet clear and protected.

Recommended plant varieties

Although native plants work best, you can try anything you like. If it doesn’t survive, don’t give up; just fill in that space with another variety.

Over a two-year period of time, McQuillan had plants die but replanted with other hardier varieties. That’s part of the fun; although, one downside is the difficult access once plants are established, she said.

Some recommended perennials are Bleeding Heart, Coneflower, Marsh Marigold, Blue Flag Iris, Black-eyed Susan, Rush, and Sedge.

Shrubs that work well include Currant, Elderberry, Mock Orange, Huckleberry, and Oregon Grape.

Concerns about rain gardens

During the first couple of summers, rain gardens need water thoroughly and deeply, at least once a week to encourage deep roots and vigorous growth.

Rain gardens are not designed to hold water more than a few hours, but they are meant to absorb the water. Mosquito larvae need several days to hatch, so if the garden is created correctly, it should not become a breeding ground. On the contrary, the gardens attract insects and wildlife that control mosquitoes.

Weeds may be a problem while the garden is being established. Weed cloth and compost can help keep down the amount of weeds…of course there’s always pulling them by hand.

“Except for weeding,” McQuillan said, “you don’t really have to do much.”

For more information on rain gardens look up Washington State University extension agency’s website at http://clark.wsu.edu/volunteer/ws/ws-raingardens-8-08.pdf.