Multi-Family and Non-Residential: Rain Garden

The application period for the Stormwater Utility credit program is officially open now through February 28, 2025. The County Board approved additional enhancements to the credit program at the December Board meeting. The presentation and Board report are available here.

Definition: Rain gardens use vegetation and soil media to aid in the infiltration and storage of rainfall and stormwater runoff.

Guidelines: A rain garden is a bowl-shaped landscaping area that allows stormwater to collect and pool following a storm. Natural underlying soils are amended with compost or replaced with a soil mix to increase infiltration, and the area is planted with native plants to absorb water and filter out pollutants.

A rain garden guidance document is available on the County’s website to provide guidance 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%

Minimum: 200 square feet

Frequency of re-certification: Every 2 years

Required Documentation:

Documents	Additional Information
Before photos (must be recent)
Diagram showing size, location, and water drainage source
Recent 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 receipts Plant receipts (if purchased) or close-up recent photos of plants. (or contractor invoices)	2-3” Double-shredded hardwood mulch For plant options, see Appendix B of Rain Garden Design and Construction: A Northern Virginia Homeowner’s Guide: http://www.fairfaxcounty.gov/nvswcd/raingardenbk.pdf
Recent photos which document mulch, planting, and depressed ponding area (target 6 inches) €Recent photo of entire rain garden €Recent perspective photo with nearest structure in background
Credit Re-certification
Recent photo of entire rain garden Recent perspective photo with nearest structure in background

Tips for success:

Take photos in recent 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. 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 re-certification: Rain Garden overtaken by weeds and/or grass; photo documentation does not show plants during growing season.