Bioretention (rain garden)
Bioretention facilities, also called rain gardens, use engineered soils and specific plants to trap and uptake pollutants in stormwater. Often located along roads and in parking lots, bioretention cells also store stormwater, which is meant to drain within 48 hours. Excess stormwater overflows to an adjacent drainage system. Treated water is either infiltrated into the underlying native soil or collected by an underdrain and discharged to drywells or surface water.
Routine maintenance throughout the year is necessary to keep your bioretention cells functioning properly. Maintaining plants, soil, and mulch helps ensure optimum infiltration, storage and pollutant removal capabilities. The majority of routine maintenance procedures are typical landscape care activities that can be performed with common tools.
Virtual tour
Click on the image below to get inside of a bioretention cell (rain garden) and learn about common components and maintenance tasks.
Where to find it:
Bioretention cells are typically found along roads and in parking lots. There can be multiple cells throughout a neighborhood or in a parking lot.
When to maintain it:
Remove sediment and clear curb cuts in late fall and early spring. Remove weeds and water new plants throughout the summer and early fall. Water new plants for the first three summers. Remove weeds and clear litter and debris throughout the year as needed.
What you'll need:
- rake
- bucket lined with trash bags
- gloves
- safety equipment (cones, high visibility clothing, etc.) if working near traffic
You many also need a shovel, mulch, replacement plants and water for irrigation.
Tools you'll need:
Before:
After:
Bioretention cells needs maintenance in these areas:
Weeds
meant to be there. Pull weeds early before
they go to seeds.
Plants
during the first three summers. Contact your local
jurisdiction for a list of approved plants.
Mulch
survival. Arborist mulch is effective, low cost
and may be required by your jurisdiction.
Trash and debris
Curb cuts
information on maintaining curb cuts.
Overflow
Riprap
Click on the photo for more info.
Maintenance sheets
Maintenance is needed if you see these signs
this biofiltration swale.
Bare, exposed soil without mulch cover
Pest infestations, including rodent holes or mounds that disturb water dispersion flow paths and damaged vegetation
Large amounts of pet waste
Inlets or outlets clogged with leaves, trash or sediment
Water ponding for more than 48 hours after the end of a storm
Erosion around inlets, outlets and on slopes
Sediment buildup, usually near inlet
Unhealthy or dead vegetation
Blackberries or other problem vegetation
Diseased or dead vegetation
Leaves, trash and other debris
Tips for fixing problems and general maintenance
Remove weeds such as blackberries and English ivy, then check for them on a regular basis and remove new vines. Contact Clark County Vegetation Management (360) 397-6140 for information.
Prune trees and shrubs and remove dead plant material regularly.
Replace vegetation damaged or removed during maintenance.
Avoid using fertilizers, herbicides, or pesticides in facility. These chemicals pollute the water and can cause unwanted plant growth.
Mulch areas annually with 2-3 inches of compost in the bottom and wood chips on side slopes and rim.
Maintain side slopes and replant bare areas.
Removing sediment is best done in dry months before winter rains set in.
If needed, seed and water during dry months to re-establish grass.
Identify and control source of sediment.
Check roads and fencing in the facility. They must be maintained to allow easy access.