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The success of bioretention areas is very dependent on the proper installation specifications that are developed by the designer and subsequently properly followed by the contractor. The specifications should include the procedures for installing the plants and the necessary steps taken before and after installation. Specifications designed for bioretention should include the following considerations:
The sequence of construction describes site preparation activities such as grading, soil amendments, allowance for compaction of soils, and any pre-planting structure installation. It also should address erosion and sediment control procedures. Erosion and sediment control practices should remain in-place until the entire bioretention area is completed. Ideally, bioretention areas should be constructed concurrently with final grading and permanent site stabilization operations. The contractor's responsibilities with respect to landscaping and plantings should be itemized within the contract specifications. The responsibilities include any penalties for unnecessarily delayed work, requests for changes to the design or contract, and exclusions from the contract specifications such as vandalism to the site, etc. The planting schedule and specifications include type of material to be installed (e.g., ball and burlap, bare root, or containerized material), timing of installation, and post installation procedures. Balled and burlapped and containerized trees and shrubs should be planted during the following periods appropriate for your climate. Ground cover excluding grasses and legumes can follow tree and shrub planting dates. Grasses are best seeded in late summer through early fall. Legumes typically should be planted in the spring of the year. The planting of trees and shrubs should be performed by following the planting specifications set forth in your local Landscape Manual or guidance. Maintenance needs of bioretention areas differ little from other landscape areas. However, it is important to use maintenance practices in and around bioretention areas, which will not compromise the facility’s pollutant-removal capacity. Avoid blocking inflow entrance points with mounded mulch or raised plantings blocking flow dispersion over the entire surface area of the facility. Adopting a low input maintenance regime will lessen the chance of overwhelming the facility with pollutant loadings above design capacity and will protect soil life. Reducing pesticide use will also reduce the risk of damage to bioretention plants, beneficial birds and insects, and soil organisms. Moreover, such conservation techniques can also save money. For example, switching to integrated pest management (IPM) has allowed the National Arboretum in Washington DC to cut pesticide costs an estimated 80%3. For more information about IPM and other low-input techniques see the Alliance for the Chesapeake Bay’s BayScapes publications. Maryland Cooperative Extension also has a number of publications, including Mimeo #HG 62, IPM: A Common Sense Approach to Managing Problems in your Landscape and Bulletin 350, Landscape IPM Guidelines for Integrated Pest Management of Insect & Mite Pests on Landscape Trees. BACK TO PLANT MATERIAL GUIDELINES
The above information was derived from the Prince George's County Bioretention Manual. |
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