Multi-Family and Non-Residential: Rain Garden

For more detailed information, please refer to the Stormwater Credit Manual.

Definition

A rain garden is a bowl-shaped garden that allows stormwater to collect after a storm and slowly soak into the ground. Natural underlying soils are amended with compost or replaced with a soil mix to increase infiltration, and the garden is planted with a mix of native plants to absorb water and filter out pollutants. Rain gardens use vegetation and soil media to aid in the infiltration and storage of rainfall and stormwater runoff.

Guidelines

A rain garden guidance document is provided to guide your work to achieve the best results.  The minimum documentation required to qualify for credit is shown below.

Existing or New: Both are eligible

Annual or Ongoing credit: Ongoing

Percent Credit: 10% (no duplication)

Minimum: 200 square feet

Frequency of Recertification: Every 2 years

Required Documentation

If pre-existing, provide the documentation denoted with *

• Before photos if newly installed

• Diagram showing location, size and water drainage source (new or pre-existing) *

• Photos of excavation or depth of amended soil (minimum 18 inches total)
  • 200 square feet minimum area

• Materials receipts for soil media or compost amendments (or contractor invoices)

  • Bioretention soil mix from an approved Arlington County vendor

    Click on ‘bioretention’ to find list of approved vendors OR Mixture of approximately: ·80% -90% sand ·10%-20% topsoil ·3% -5% organic matter (compost) OR Compost material should be well composted and free of viable weed seeds. Fresh manure should not be used because of its high bacteria and nutrient levels.

• Mulch and plant receipts (if purchased) or close up photos of plants (or contractor invoices) *

• 2-3” Double-shredded hardwood mulch

• For Plant options, see Appendix B of the Rain Garden Design and Construction: A Northern Virginia Homeowner’s Guide

• Photos which document mulch, planting, and depressed ponding area (target 6 inches)

• Photo of entire rain garden *

• Perspective photo with nearest structure in background *

Credit Recertification

• Photo of entire rain garden

• Perspective photo with nearest structure in background

Tips for Success

• Take photos in summer during growing season; take all required photo types.
• Follow maintenance guidelines: For the first year after the garden is installed, you may need to water the new plants if it doesn’t rain for an extended period of time. Once the native plants are established, they should be able to survive dry periods. Adding leaf mulch one to two times per year will nourish the plants and minimize the growth of weeds. Rain gardens often thrive without the addition of fertilizers or pesticides because the native plants are well-suited for this area. Remove any weeds that do appear in the rain garden by hand-pulling.

Typical Reasons for Denial of Recertification

Rain Garden overtaken by weeds and/or grass; photo documentation does not show plants during growing season.