The vegetation is a big opportunity to maximize the co-benefits of biodiversity and amenity. Planting plans can be formalized or naturalized to suit the surrounding style. In addition to aesthetic qualities, plants have specific functions in several LID practices. These include promotion of infiltration, treatment of pollutants and stabilization of soil. When selecting plants for an LID practice, aim for species with high functionality, survivability, suitability and availability. Landscape professionals should use these lists as guides, taking into consideration the appropriate planting zone, the size of the planting area versus size of the plant at maturity, tolerances to drought or periodic inundation, maintenance requirements and adaptability.
- To help you select appropriate plants for your site, we've developed tables to indicate the suitability for use in LID features.
- For resilient and robust planting, native species which can tolerate periods of drought and periodic inundation are recommended.
- Woody and evergreen plants should not be planted in any areas of the bioretention cell to be used as snow storage.
- Dense shrubby plants should be avoided in locations where the accumulation of trash is anticipated as a maintenance problem, or where their growth can hinder maintenance and inspection of inlets or other structures.
- Trees should not be planted directly over underdrains, and may be better sited at the perimeter of bioretention cells.
- Whilst it is not always necessary to use an entirely native planting palette, invasive plants are inappropriate for LID practices.
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Plant species are adapted to specific levels of moisture to achieve establishment and sustained growth. Soil moisture has been characterized by three categories: dry (1), moist (2) and wet (3). Some plants can tolerate a wide range of moisture regimes, whereas others perform optimally in a more narrow range of soil moisture conditions. Species ranked with a dash between two numbers can tolerate a range of conditions.
Plant species react differently to varying levels of sunlight and shade. Plant adaptations to these parameters are referred to in terms of degree of exposure. Most of the LID practices will be installed in newly developed areas, thereby providing exposure to full sun, meaning at least 6 full hours of direct sunlight for plantings. As trees develop over several years, or if an LID practice is installed in an area where there are existing trees or buildings providing partial shade, plants adapted to 3 to 6 hours of sunlight exposure should be used. Plants tolerant of full shade require less than 3 hours of direct sunlight each day. However, some shade-adapted species come into leaf early in the growing season in order to take advantage of full sunlight before tree leaves emerge and create shade.
Our tables indicate whether the species in question is tolerant of shade at all. For more information, consult the sources listed below.
These categories represent broad generalisations regarding drought tolerance.
The low, medium and high categories indicate the tolerance of plant species to salt exposure and/or uptake. Plant species with low salt tolerance should not be used in any LID practice receiving runoff from salted roads and parking lots. Species with medium salt tolerance can be utilised in LID practices that will be receiving road runoff but should not be in the line of salt spray or be receiving the bulk of the runoff. Species with high salt tolerance should be planted in LID practices that receive road or parking lot runoff that routinely contains road salt. Few plants are truly halophytic or “salt-loving”. In most cases, elevated salt levels are temporary and precipitation quickly dilutes and removes salt from the soil profile. The plant lists below include recommended species for LID practices likely to receive road or parking lot runoff.
Compaction and Pollution Tolerance
Development nearly always causes compaction of on-site soil, and bioretention facilities in road-right-of-ways should be pollution tolerant.
These are species which have demonstrated good performance in projects designed, installed and monitored by the Sustainable Technologies Evaluation Program.
|Plant characteristic||Potential benefit to LID performance|
|Plant mass||Higher biomass consumes more nutrients (decreases nutrient discharge from bioretention) and increases transpiration rate.|
|Growth rate||Higher growth rate consumes more nutrients, particularly in combination with root characteristics as below.|
|Root lipid content||Higher root lipids have been associated with increased plant uptake of organic contaminants such as polyaromatic hydrocarbons (PAHs)|
|Root length||Longer roots are associated with plants consuming more nutrients, although roots which reach the bottom to the media may contribute nutrient...|
|Root mass and thickness||Larger overall root mass and many dense fine roots are associated with increased nutrient uptake by plants. Thicker roots help to preserve hydraulic conductivity of the media.|
|High-nutrient tolerance||Plants adapted to high nutrient environments are likely to uptake nutrients at a higher rate.|
|Organization||Coverage||Types of Material||Website|
|Watersheds Native Plant Database||Canada / Ontario||Grasses, Ferns, Shrubs, Trees, Vines||https://watersheds.ca/plant-database/|
|Online Plant Guide||USA||Grasses, Ferns, Herbaceous, Shrubs, Trees, Vines, Ornamental||http://onlineplantguide.com/Index.aspx|
|North American Native Plant Society||N. America||Grasses, Ferns, Herbaceous, Shrubs, Trees, Vines||http://www.nanps.org/plant/plantlist.aspx|
|United States Department of Agriculture||N. America||Grasses, Ferns, Herbaceous, Shrubs, Trees, Vines, Ornamental||https://plants.usda.gov/java/|
- Leaf and fruit identification for trees and shrubs
- Hunt, W. F., Lord, B., Loh, B., & Sia, A. (2015). Plant Selection for Bioretention Systems and Stormwater Treatment Practices. Singapore: Springer Singapore. https://doi.org/10.1007/978-981-287-245-6
- Muerdter, C.P., C.K. Wong, and G.H. LeFevre. 2018. Emerging investigator series: the role of vegetation in bioretention for stormwater treatment in the built environment: pollutant removal, hydrologic function, and ancillary benefits. Environ. Sci. Water Res. Technol. 4(5): 592–612. doi: 10.1039/C7EW00511C.