Rain gardens are a great way to both have an attractive landscape feature and also enhance water quality in the drizzly Pacific Northwest. Forests and soils act as a filter for rainwater, cleaning it and releasing it slowly into creeks, streams, wetlands, lakes and eventually the ocean. Rain that falls on solid surfaces such as sidewalks, roads and roofs, collects the pollutants on these surfaces, bypassing the natural filter process, and carries them directly into waterways such as the Columbia river.
As more land is developed for human use, the amount of impervious surface increases, delivering ever more polluted runoff to these water bodies, where we swim, fish and play.
Rain gardens are designed to gather, soak up and filter rainwater coming from any surface water can’t move through. They function as temporary ponds, filling with the water running off these surfaces, holding it and allowing it to soak into the soil where it is filtered and cleaned. In this way, rain gardens prevent pollutants from reaching natural water bodies.
These special gardens add external appeal to the home landscape, reduce flooding and erosion issues, create habitat for wildlife and recharge local groundwater.
With careful planning and some sweat equity, homeowners can install their own rain garden. Selecting an appropriate site is important so check with your municipality on specific regulations and to have existing utilities located.
A rain garden should be placed where it can drain selected hard surfaces efficiently, but it should be at least ten feet from any building foundations. Other things to avoid are buried utilities, steep slopes, septic tank and well areas, existing intact natural areas, and spots with high existing ground water. You’ll also need to find out how fast the soil of your rain garden drains.
When building a rain garden, a variety of tools and materials are needed for things like marking the garden shape, excavating, planting, and mulching. You may also need soil or soil amendments depending on the type of existing soil in the location. Drain rock, gravel and larger rocks or boulders will also be very useful. You’ll also need mulch and some fabulous plants!
Your rain garden should include an entry point for water coming from the hard surfaces you are draining. This might be a downspout, pipe, or perhaps a dry creek bed connecting the spaces. The size of the garden will be determined by the size of the area it is draining and how quickly your soil drains. The garden will need a level, excavated bottom, an overflow point, and properly prepared soil. Water entry and exit points must be lined with drain rock and possibly larger rocks to prevent erosion and silt movement as the water moves into and out of the garden.
There are many great plants which will grow happily in a rain garden. Rain gardens are divided into three planting zones. Zone 1 is the bottom of the garden; plants here need to be very tolerant of wet conditions. Zone 2 plants are on the side slopes of the garden and need to handle occasional standing water. Zone 3 is the top edges and perimeter of the garden. Plants growing here must do well with normal to dry soil conditions. There are many lovely plants both for sun and shade which can be included. Selecting plants that are drought tolerant once established will allow your rain garden to function without supplemental water. The first one or two years, you will need to provide some extra water for young plants to help them develop and ‘stand on their own roots’ without extra water support.
Select a mix of plant types – small trees, shrubs, and perennials. Remember to base your selections on their mature size to avoid overcrowding. Ultimately, a mature rain garden should have 90 percent to 100 percent of its bottom covered with plants. Narrow your choices based on your individual preferences and interests. Grasses and grass-like plants, evergreens, plants for beneficial insects and wildlife, fragrant flowers, natives. There are many options for multi-seasonal beauty.
After your garden is planted, it should be mulched with a good quality natural wood mulch – avoid colored mulches, grass clippings and mulch from questionable source wood like chemically treated pallets. Place a sturdy drain rock layer around the entry and exit points instead of mulch. You can also add extra rocks, gravel or boulders to create accents here and there in the garden, enhancing its natural look.
As your rain garden matures, you’ll need to do routine maintenance to keep it looking attractive year-round. Avoid using fertilizers and pesticides in your rain garden if possible. Weeding will always be necessary but should lessen as plants take up more space. Occasional top-dressing mulch, seasonal pruning and clean-up might be necessary as well as removal of any general debris which falls into the garden. Watch out for erosion, areas where this occurs should be repaired and stabilized with extra drain rock and larger rock pieces if necessary.
Your personal rain garden can do great things for your own garden happiness and home environment. The awesome bonus is it also does great things for the health of the very special part of the country we live in.
To learn more about rain gardens, attend the upcoming “Let it All Soak In: A Rain Garden Webinar” from 6:30 to 8 p.m. April 13. A stunning landscape feature and stormwater device all in one, rain gardens are a unique way to protect the water quality of your local creek, lake or the Columbia River while spiffing up the garden at the same time. Come away with a solid understanding of rain gardens –their benefits, suitable locations and tools for design and installation.
Attendees of this 90-minute webinar led by Colleen Miko will learn about rain garden plants for sun and shade and become familiar with the “Rain Garden Handbook for Western Washington Homeowners.”
WSU Clark County Extension Master Gardener Program will host a free webinar in collaboration with Clark County Public Health’s solid waste outreach, from 6:30 to 8 p.m. Tuesday, April 13. To register in advance, visit bit.ly/3cDItdJ
After registering, you will receive a confirmation email containing information about joining the meeting. Email Erika.email@example.com or call 564-397-5738 for more information.
Christine Anderson is a master gardener with Washington State University Extension, Clark County.