Green Infrastructure

A biorentention area is a shallow stormwater basin or landscaped area with well-draining soils such as sand, fines, organic matter, and vegetation to capture and treat stormwater runoff.

Routine maintenance should be performed on bioretention areas. During the first year that the bioretention area is built, maintenance may be required at a higher frequency to ensure proper establishment of vegetation in the practice.

In addition to routine maintenance, bioretention areas require seasonal and intermittent maintenance. For example, in case of snow, ensure that snow does not pile up in the bioretention area. During the winter, trim plants and make sure the materials used to de-ice surrounding areas stay out of practice to avoid clogging and further pollution.

After a large rainstorm, keep drainage paths, both to and from the area, clean so that water can properly infiltrate into the ground. Mulch the area as needed to keep a thickness of 3-4 inches. Shredded hardwood mulch is preferred. For more information on vegetation in bioretention areas, see [Link to Appendix D: Planting and Soil Guidance].

If the bioretention area is not draining properly, check for clogging in the inlet and outlet structures.

Fertilizers and pesticide should be used sparingly and only if necessary.

Some of the common problems to be aware of when maintaining a bioretention area include, the following:

• Sediment build-up
• Clogging in the inlet and outlet structure
• Establishing vegetation within the bioretention area
• Clogging the underdrain (if applicable)
• Mosquitoes breeding in the practice
• Ant mounds
• Maintaining the proper pH levels for plants
• Pruning and weeding to maintain appearance

Should the bioretention area become a breeding ground for mosquitoes, the problem is likely with the soil media or the overflow structure. 

Bioretention Area Routine Maintenance Schedule
Schedule	Activity
As needed or 4 times during growing season	Prune and weed to maintain appearance. Dissipate flow when erosion is evident. Remove trash and debris. Remove sediment and debris from inlets and outlets. Remove and replace dead or damaged plants. Mow around the bioretention area as necessary, ensuring grass clippings are not placed in the area. Observe infiltration rates after rain events. Bioretention areas should have not standing water within 24 hours of a storm event. Inspect for evidence of animal activity
Semi-annually in spring and fall	Inspect for erosion, rills, or gullies and repair. Inspect filter strip/grass channel for erosion or gullying, if applicable. Re-seed or sod as necessary. Inspect trees and shrubs to evaluate their health, and remove and replace any dead or severely diseased vegetation. Obtain a mulch depth of at least 3 to 4 inches should be inspected and obtained. Additional mulch should be added as necessary.
As needed or during winter months	Trim planting material. Inspect for snow accumulation.
Annually	Testing the planting soils for pH levels. Consult with a qualified licensed professional to determine and maintain proper pH levels.
2 to 3 years	Replace/repair inlets, outlets, scour protection or other structures as needed. Implement plant maintenance plan to trim and divide perennials to prevent overcrowding and stress. Check soil infiltration rates to ensure the bioretention area soil is draining the water at a proper rate. Re-aerate or replace soil and mulch layers as needed to achieve infiltration rate of at least 0.5 inches per hour.