Handling Rainwater in Your Garden

by Ben Bowen
rain water in portland landscapes

I am not going to start this by talking about how much it rains in Portland...

But when that rain hits your roof, ADU, driveway, and landscape what happens? Some of it soaks into the ground (great). But much of it is collected in gutters and drains. It then goes either to a treatment facility and then to a river or, in some locations, directly into a stream or river.

The problem with this is twofold. First, water treatment is expensive and requires a lot of infrastructure. Look at your water bill. You most likely pay more for the the water leaving your property than the water coming in. Second, stormwater picks up pollutants from roofs, driveways, lawns, and streets. If those pollutants go directly into streams they cause problems.

You can do something about this. Instead of burdening streams or waste water systems with water from your property you can catch it. Wondering how to catch it and what to do with it? Here are a few of the ways to manage your rain water:

Rainwater Management Guide For Portland Homeowners


Step 1: Capture The Rain

Before you can do anything with stormwater you have to catch it. Your house most likely already has ways to do this. Gutters and downspouts direct roof water. Surface drains collect water from driveways, patios, and landscapes. French drains collect surface and subsurface water.

Where does your water go from there? If you home is not new-ish and if you have not disconnected these from city stormwater lines then they are going to treatment plants and/or rivers.

To capture this water you have to interrupt the supply by disconnecting from the city's system. Portland wants you to do this! There is even an incentive program, which you can check out here.

Disconnecting downspouts is pretty simple. You simply take your downspout out of the drain line near the ground and then direct the water elsewhere (more on that in a second).

If your surface or French drains connect to the sewer you are going to need to work a little harder. These connections are underground, and you may have no idea where they are. Contacting a landscaper or drainage specialist may be in order.

Ah, but what if you have surface water and soggy areas but no drains? Then you need to install them- and move to the next step.


Step 2: Manage The Rain

We are now capturing much of the rain that hits your little piece of Portland (or Beaverton, Lake Oswego, whatever). Pat yourself on the back but don't pull a muscle because there is still work to do. Now it is time to do something with all that water.

The ultimate goal is to return it to the ground. Running lines from all your collection points to a dry well, or multiple dry wells, will allow the water to slowly percolate into the soil. This solution is elegant and pretty simple. It can be more complicated if you have really, really, bad clay. But for most of the Portland area that is not a big worry.

Dry wells may be the simplest solution, but there is more that you can do. You need a rain garden.

Taking the water to a rain garden adds another layer of goodness to your endeavor. Now you are not simply getting water into the ground but also using plants to add another layer of filtering. 

Dry wells can be part of the plan when you are building a rain garden, either to add water capacity below ground or to handle overflow if the rain garden gets full. With or without a dry well a rain garden is basically just a place where rainwater can be stored until it can soak into the ground.

Done properly a rain garden is the ultimate landscape win-win situation. They are extremely practical and should be beautiful as well. Rocks can be used to create a feature that is not a mud pit and that looks good even when the weather is dry. Rain garden plants (see list in sidebar) can handle the bog/dry cycle and put the "garden" in rain garden.

Many homeowners are taking space that was previously lawn and turning it into a rain garden. Now they use less water on the landscape, don't need to fertilize as often in addition to all the other benefits. I think you can see why rain gardens are a key component of my imaginary 'guilt free' gardens!

Here at Ross NW Watergardens we try to design rain gardens that blend into the landscape, so no one even realizes what a workhorse they are! You can read more about designing rain gardens here. And this book will help you design your own beautiful rain garden.

What if you don't have the space for a traditional rain garden? Consider a container stormwater garden, which requires a lot less space. This article from EMSWDC will show you exactly how to do it.

Step 3: (optional) Use The Rain

Yep, you can take this even further if you want. Instead of simply returning the water in a respectful way you keep the water until you can use it to water your existing plants.

Rain catchment systems can be as simple as a rain barrel with a hose bib at the bottom. Larger scale systems exist that can hold thousands of gallons and then dispense them using a pump.

Regardless of scale, the concept is very simple: store the rain water and then use it during our dry summers. Watering your vegetable garden in August with water that fell in February is pretty cool.

Need help designing and installing one of these systems? Leave a comment below and we can talk.

Maintaining Your Rain Garden

Rain gardens are generally low maintenance, especially when they are installed properly. But a little care will keep them functioning properly and looking great. The basic of rain garden maintenance:

  • Keep all drains, pipes, and overflows free of debris. It is a good idea to check these in December, after most trees have dropped their leaves to make sure the water can easily flow to the garden. A couple average sized maple leaves can block a drain and send that precious water into the street!

  • Remove weeds, exotics, and invasives from the rain garden. One of the big problems with invasives (like horsetail) is the way they can clog small natural streams. Don't let your rain garden become a distribution point!

  • Periodically clear the area of fallen leaves, dead grass, and other debris. This will keep you and the neighborhood happy with the appearance of your rain garden.

For a more detailed look at maintaining a stormwater management system visit this guide from the City of Portland.

A downspout connected to a dry well.

A downspout connected to a dry well.


Stormwater Planter Plant List

Latin name – Common name

Evergreen Groundcovers

Carex densa – Dense sedge

Carex stipata – Sawbeak sedge

Carex obnupta – Slough sedge

Deschampsia cespitosa – Tufted hairgrass

Juncus patens – Spreading rush

Flowering Accent Plants

Camassia quamash – Common camas

Mimulus cardinalis – Monkey Flower

Lupinus polyphylus – Large-leaved Lupine

Lupinus rivularis – Stream Lupine

Source: City of Portland, Vegetated Stormwater Facilities in the Public Right of Way, 2007

rain barrels hold water for plants
rain garden we designed

Yes, it does rain a lot here in the PNW. But if you catch that water, let it filter naturally back into the ground, and maybe even use it to beautify your yard? Well then let it rain, let it rain.

Looking for more rain garden ideas? Check out the great examples in the galleries below:


Rain Garden Pictures: