Rain Gardens in Planting Strips

Our recent sunny weather may have you thinking about the best ways to sneak out of work early, but summer is also a great time to start planning for a rain garden in your planting strip this fall!

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Rain gardens are shallow, planted depressions that collect runoff from surrounding paved surfaces, where it slowly seeps into the soil and filters out pollutants.

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Building a rain garden in your planting strip – Design

It’s important to select a good location for your rain garden:

  • Curbside rain gardens may be located in the planting strip adjacent to your property, between the sidewalk and curb.
  • The street slope must be less than 5% – in other words, there is less than a five-foot change in elevation per every 100 feet.
  • The planting strips must be at least 5 feet wide.
  • Water must drain through the soil at a rate of 0.3 inches per hour.
  • Light poles, fire hydrants, and other utility structures should be located at least five feet away.
  • Don’t pick a site underneath the canopy of a tree in the planting strip, where digging will disturb its roots.
  • Native and drought-tolerant plants are great for rain gardens. Choose low-growing or dwarf plants that do not grow taller than 3 feet. Near intersections and driveways, plants should be no taller than 30 inches.

Permit Application

A permit for a rain garden is free, but SDOT’s Street Use Division requires:

  • A Street Use Construction Permit Application. Pick up an application in-person at the front desk of Floor 23 of the Seattle Municipal Tower.
  • Or download a fillable pdf and email it to us at: SDOTPermits@seattle.gov.
  • A Right of Way Impact Site Plan. Get a template here.
  • A drawing that shows the length and width of the rain garden, a cross-section, and a plant list.

Installation

After your permit is approved, you’re ready to build your rain garden! The best time to start digging is between May 1 and September 30. This season is recommended to give you plenty of time to put in any necessary erosion and sediment control measures.

Planting anytime during the fall or early spring is recommended to take advantage of natural rainfall.

Maintenance

Rain gardens located in the public right of way will require some TLC. At a minimum, the plants will need a deep soak every three to four days for the first two summers to help the roots establish, as well as weeding and mulching in the spring and fall. Occasional pruning may be necessary if the plants grow too tall. For more tips on taking care of your rain garden, see the Rain Garden Care Guide.

Since voluntary curbside rain gardens are considered beautification projects, the permit is free. However, voluntary curbside rain gardens do not fulfill any Seattle Stormwater Code or Seattle Green Factor program requirements, and are not eligible for RainWise rebates.

If you have any questions or would like additional information about voluntary curbside rain gardens, please contact Shannon Glass at shannon.glass@seattle.gov.