What Are Planters?
Planters are concrete walled landscape areas that capture, store, and filter stormwater runoff. They can be designed for full or partial infiltration. They can be lined if conditions do not allow for infiltration.
How Planters Work
Planters collect and temporarily store runoff. Depending on the soil infiltration rate, planters will either allow the water to slowly soak into the soil (infiltration planters) or collect the water and then pipe it to a safe location to drain or into the stormwater system (lined planters). In both cases, the planters help by collecting and slowing down stormwater runoff while plants and soil filter the runoff to improve water quality. Planters come in many shapes and sizes.
Summary of Design Requirements for Planters
These site and design requirements can help you decide if stormwater planters might be appropriate for your project. Consult the Stormwater Management Manual for complete requirements on sizing, placement, and design for planters.
- The maximum slope of the finished grade of the planter is 0.5 percent in any direction.
- The minimum width of a planter is 2 feet, measured from the inside.
- Choose a soil from the City Blended Soil List for proper infiltration rate. Consult the Stormwater Management Manual for more information.
- A fully lined planter is required when building on or near steep slopes or where there is contaminated soil.
- No setbacks are required for lined planters. For infiltration planters, to stay safe and avoid damaging buildings, consult the Stormwater Management Manual for the required distances from foundations, basements, and property lines. If you have a drainfield or grade changes on your property, additional setbacks are required.
For best results, keep in mind the following construction considerations:
- Protect the subgrade from over-compaction during excavation. Keep equipment out of the excavation and do not store materials there.
- Prevent runoff and sediment from filling the site during construction.
- Planters require specific plants that perform well in wetted/ponding conditions. See the Stormwater Management Manual’s plant list and select zone A and B plants:
When to Call a Professional
When using the simplified approach described in the Stormwater Management Manual, a designer is not required.
You will need a professional designer:
- If your site is larger than 10,000 square feet.
- If the infiltration rate is less than 2 inches per hour.
- To downsize the planter if infiltration rates exceed 2 inches per hour.
- If the planter is large enough to avoid the requirement for a piped overflow.
Costs and Permits
Planters range in cost depending on the size and type of system.
A permit is needed to install planters. Your permit application will be reviewed by at least two City bureaus:
- The Bureau of Development Services will require a site development permit.
- Environmental Services will review the stormwater components. Find permit application requirements in the Stormwater Management Manual.
Maintenance for planters is like that for other landscaped areas. Inspect planters on a regular basis and complete maintenance.
- Water the plants deeply once a week during dry months (May to October) to encourage root growth and keep plants strong, especially while plants are getting established during the first two summers.
- Pull weeds by hand before they become established (avoid chemical weed killers).
- Remove sediment and debris, watch for erosion, and replace plants as needed.
- Regularly check gutters, downspouts and inlet pipes to ensure they are free and clear of debris and rainwater can enter the garden.
- Once a year, layer compost or mulch 2 inches deep to suppress weeds and feed plants.
- Thin and prune plants as needed. Divide dense plantings every two to five years.
- Remove leaves in the fall. Leaf build-up reduces the planter's capacity and can smother plantings.
With adequate maintenance, planters can last indefinitely.
Stormwater Management Manual
Consult the City’s Stormwater Management Manual for the complete set of requirements on how to safely site, build, and maintain planters or other stormwater management solutions on your property.
Portland's Clean River Rewards Program
Residential and commercial property owners who install qualified stormwater management solutions may be eligible for discounts on the stormwater charges of their sewer, stormwater, and water bill through Portland's Clean River Rewards.
Find More Resources
When selecting plants for your planters, see the Stormwater Management Manual Plant List for suitable native and non-native plants. Planters need plants best suited for zones A and B.
Vendors of the required soil blend can be found in the City’s list of Soil Vendors. Permission is required for alternative blends.