Snoqualmie Valley Master Garden Ask: A Rain Garden? In the Pacific Northwest?

In this month’s guest article, Snoqualmie Valley Master Gardeners walk you through the ins-and-outs of rain gardens – from what they are, to how they work, why they were created and how to build your own.  They also provide a list of deer resistant plants for you – if you’ve been battling local deer hunger in your yard this summer. 

What exactly is a rain garden?  

Lately, we have been hearing a lot about rain gardens in the news.  A rain garden is a sunken, generally flat-bottomed garden bed 18-30 inches deep that is designed to collect and filter storm water runoff from rooftops, driveways, sidewalks, parking lots and streets.  The concept behind rain gardens is that they help mimic raingardennatural forest conditions by filtering rain water from hard surfaces to keep the water from going straight to our lakes, rivers and the Puget Sound.  As the Puget Sound landscapes have become more developed, the rainfall that lands on hard surfaces is routed into pipes, ditches, and storm drains, and much of that is routed directly to streams or into the sewer system, untreated.  The polluted rainwater runs unfiltered straight into the Puget Sound.  Between 14 million and 29 million pounds of pollutants enter the Sound every year according to the State Department of Ecology.

What can a rain gardens do for me?

Ultimately, rain garden benefits result in healthier waterways, fish, wildlife, and people.  Rain gardens keep our watersheds healthy by reducing flooding because they absorb rainwater from hard surfaces around our homes and filter out toxic chemicals like oil, copper, lead, phosphorus, and nitrates before they pollute our water supplies.  In addition, rain gardens also slow down water run-off thereby recharging groundwater aquifers by allowing water to slowly soak into the ground.  As if that were not enough benefit, they also provide beneficial wildlife habitat in our home gardens for birds and other creatures.

How do you build a rain garden? 

Rain gardens must be designed carefully to capture and treat storm water on-site and send any excess overflow during a large rainstorm off-site, without damaging structures and other property.  Some cities and counties have specific regulations regarding disconnecting downspouts, routing or piping water off-site, and setbacks to structures.  If you plan on building a rain garden check with your local planning department to find out what the regulations are for your home location.  The figure here (courtesy of WSU Rain Garden Handbook, 2013) shows the different layers or zones involved in a rain garden.

Some of the steps you must consider before you begin are:

  • Is your site’s soil drainage adequate?
  • Where is the best location for the rain garden?
  • What size should my rain garden be to handle the run-off in my yard?
  • What shape is best for my landscape?
  • What plants will do the best job in my rain garden?
  • What type of soils will I need to add into the rain garden so it drains and filters properly?

An indispensable handbook is offered free of charge by WSU and can be downloaded at their rain garden website.  It will answer all these questions and gives a step-by-step guide on rain garden construction.  The rain garden researchers at WSU have done all the calculations for you and have laid it all out in layman’s terms.  The Handbook also helps you find qualified people to assist you.  There are also organizations that will possibly help you with the cost of installing a rain garden. For community assistance, also check out the  12,000 Rain Gardens in Puget Sound Campaign – they want to establish 12,000 rain gardens in the Puget Sound region by 2016. Want to join in the fun?

Plants We Love: Deer Resistant Summer Flowers

Gardens that double as free range for deer and other wildlife aren’t often sites for colorful blooms. The garden may start off with lovely flowers, but once the deer find them, the blossoms are bitten right off as soon as they bloom. The key then, is to plant flowers that the deer don’t find appealing.

Russian Sage. Often mistaken for lavender on steroids, Russian sage (Perovskia atriplicifolia) is a stunning semi-woody perennial for a full sun, drought tolerant russian_sage_algarden. The browsing deer don’t find it at all tasty, but the bees love it. Depending on the variety and climate, this plant will bloom from early summer into fall with tall wands of lavender or blue flowers and silvery, deeply cut, aromatic leaves.  It has an airy appearance, growing 3 to 5 feet tall and about 3 feet wide, and provides an excellent backdrop in perennial gardens. Unlike some other perennials, however, Russian sage can remain in the garden for winter interest and can then be pruned short in early spring.

Coneflower. Daisy-like flowers with raised centers, coneflowers (Echinacea purpurea) are the perfect companion to Russian sage. Blooming also from early coneflowersummer into fall, coneflowers are disease and pest resistant (even from the 4-legged varieties), need very little water once established, and provide a colorful vista in any sunny garden. Varieties can provide blossom colors from white to purple to orange, and range in height from 2- to 4-feet tall. Coneflowers make good fresh and dried cut flower arrangements, but leave some of the flower heads for winter to attract a variety of birds to feed on the dried seeds.


Additional information on rain gardens and deer resistant plants can be found on our website at Bring your gardening questions to the Snoqualmie Valley Master Gardeners at the North Bend Farmers Market through mid-September.

[The authors, Beverly Ann Morrow and Ann Acton, are master gardeners in the WSU Extension Master Gardener Program; Bev is also a Rain Garden Educator. Extension programs and employment are available to all without discrimination. Evidence of noncompliance may be reported through your local Extension office.]

Comments are closed.

Living Snoqualmie