Plant lists

Wonderful plants varying in form, texture and colour, TBG ON

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 (see page links under Plant Selection).
• 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 portions of the LID facility to be used for snow storage during winter months.
• Trees and shrubs should be offset from inlets and overflow outlet locations, and lowest-elevation portions of the LID facility, where sediment, trash and natural debris will accumulate, to ensure access for completing routine inspection and maintenance tasks is not hindered.
• Trees should not be planted directly over underdrain perforated pipes and may be better located at the perimeter of LID facilities instead.
• While it is not always necessary to use an exclusively native planting palette, invasive non-native plants (i.e., invasive exotics) should not be planted in LID practices.

Plant Selection

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Select trees Select shrubs Select perennials Select climbing plants Select tall grasses Select plants for green roofs Select plants for wetlands

Plant Characteristics

Soil moisture

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.

Shade tolerance

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.

Drought tolerance

These categories represent broad generalisations regarding drought tolerance.

Salt 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.

STEP stars

These are species which have demonstrated good performance in projects designed, installed and monitored by the Sustainable Technologies Evaluation Program.

Advanced plant selection criteria

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.

Overview

A common characteristic of bioretention cells is that they have shallow earthen slopes, less than 2H:1V. The design of a bioretention cell allows for several different planting zones. Bioretention cells are suited for institutional, commercial, industrial, and residential multi-unit/multi-story land-uses. They are can be sited in large landscaped areas, parks, parking lot islands, or any areas where there is space for shallow earthen slopes and the multi-zone planting aesthetic is appropriate.

Drainage areas

There are two basic categories:

1. Exposure to roadway or parking lot runoff. Runoff is contaminated with deicers and vehicle pollutants. These can take on several forms, including parking lot islands, traffic islands, roundabouts, or cul-de-sacs and are often used as snow storage location
   • Select salt tolerant grasses, other herbaceous material and shrubs.
2. No exposure to roadway or parking lot runoff. These receive runoff from rooftops or areas that use no deicing salt and have low pollutant exposure, such as courtyard bioretention.
   • Practices allow for a greater range of species selection.

Other selection factors:

• Most bioretention cells will be situated to receive full sun exposure.
• Facilities with a deeper media bed (1 m or greater) provide the opportunity for a wider range of plant species, including trees.
• The inclusion of vegetation with a variety of moisture tolerances ensures that the bioretention cell will adapt to a variety of weather conditions.
• Proper spacing must be provided for above-ground and below-ground utilities, and adjacent infrastructure.

Selection of plant species suited to tolerate the varied conditions common to green infrastructure is essential for the success of a planting plan. A plant’s ability to tolerate flood conditions is further correlated to its age, adaptation to the site, and condition. A well-established plant has greater reserves to withstand flood events. While it is recommended to leave the LID practice offline until plants become established (one to several years), in most instances this may not feasible. Measures incorporated into the LID practice such as erosion and sediment controls and pre-treatment cells can moderate flows enhancing survival potential. In all cases, soil surfaces must be stabilized prior to allowing flow to enter the LID facility.

Selecting plant material that will be appropriate for a particular site should take into consideration the local context or setting. Some species, especially rare or potentially aggressive species, are not always conducive to the type of site or objective of the project, especially in areas near or next to natural communities. For example, a green roof that is isolated from all natural areas may be ideal for regionally rare species that are specially adapted to conditions of high exposure and shallow soils. Among the questions that should be asked are:

• Is this LID site located within, adjacent or close to a natural area? Or, is this LID site location isolated (i.e. beyond 120 m of natural feature) from the natural environment?
• What is the composition of the nearby natural area?

Native, introduced and rare plants

The goal of planting design for LID practices is to achieve a sustainable vegetation community that is tailored to the ecological qualities of the site and the aesthetic considerations of the landowner. Plant selection for LID practices is predicated on the principle of ‘right plant for the right place'. Many LID practices are carried out within a highly urbanized context that poses unnatural stresses on plant growth and survival. This guide provides general recommendations to direct species selection. Landscape professionals should use this information to generate specific plant lists that are tailored to the conditions prevalent on site while addressing surrounding urban and natural land uses.

Native and introduced species

Native plants have co-evolved with the local ecosystems and natural processes. They are genetically better adapted to local climate, soils, insects and diseases of the area, and may require less maintenance to ensure health and survival. Working with native plants helps protect local native biodiversity, allows the LID feature to function ecologically while creating a more diverse, naturally-beautiful, landscape. Where conditions for growing native plants are inhospitable, diversifying the planting palate with introduced species may have a more successful result. In addition to native species, many introduced plants are grown in nurseries and garden centers and are readily available to landowners.

Some introduced species escape from gardens and other managed landscapes and begin to reproduce in the wild. Invasive plants are typically non-native plants that out-compete native species. These species lack natural predators, grow aggressively and reproduce rapidly and can be problematic in the natural environment. Invasive species have not been included on the recommended plant list for LID practices and should not be planted in any situation.

Recommendations:

• In all applications of LID, designing with native plant species is the preferred and strongly recommended option.
• In areas containing, adjacent to, or within a linkage to an existing natural heritage feature, native plants should be used exclusively. In areas regulated by a conservation authority, native plants will be required for approval.
• In settings that have restricted or harsh conditions for plant growth (e.g. limited root volume, unusual patterns of drought and/or inundation, exposure to salt, sun, wind, shade and pollutants) introduced species can be used to substitute/augment native species selection. Introduced species shall be chosen to be functionally and aesthetically appropriate for the location.
• Introduced invasive species should not be planted as these can compromise the function of an LID practice, the ecology of nearby natural areas and can lead to higher maintenance costs. Non-native invasive species have not been included in the LID plant list.
• Except unless otherwise noted, the use of cultivars of native plants should be avoided.
• When sourcing native plant material, especially from commercial nurseries and garden centres, always refer to the scientific (botanical) name for the desired plants. Confusion over cultivated varieties of plants can be avoided by asking questions of the staff to ensure that only the correct native varieties are sourced. Species that are often mislabelled and other common concerns are noted in the Plant lists.

Rare Species

Some of the native plants in the LID plant list are ‘rare’ and/or ‘uncommon’ within the Province of Ontario . STEP do not support the incorporation of rare native species in planting plans and designs unless locally sourced material can be obtained and there is little to no threat of escape into naturally occurring populations. Genes from plants adapted to other areas can inadvertently introduce harmful traits that weaken the ability of the native population to thrive. Rare species are not always appropriate for LID practices depending on the project objectives or the characteristics of the site, especially in situations where rare species may be planted near natural communities. In these situations, the opportunity for genetic contamination of native populations is higher and the planting of rare species is unadvised. Some native species are rare because they require specific habitat conditions in order to grow which may not exist or be able to be restored easily. The benefits to landscaping with native, common plant material is that plantings may be better adapted to a wider range of conditions, and may tolerate more disturbance. A higher success rate and lower maintenance requirement may be achieved.

The method and collection of native plants is an important consideration when sourcing rare plant material. Ecologically responsible methods of seed collection and propagation ensure that wild populations are not over harvested and that they have the ability to keep adapting over time. Seeds should not be collected or existing plants relocated from the wild for use in LID practices. When sourcing material from growers and nurseries, the plant material origin should be confirmed as well as its method of collection and propagation. Recommendation: In areas containing, adjacent to, or within a linkage to an existing natural heritage feature, common native plants should be used exclusively. In areas regulated by a watershed authority rare species are not suitable for planting unless the local source/provenance is documented and approved. Rare species should only be used sparingly when there are no suitable common species available and reasons for selection should be provided. Where rare species are included in a design, it should be ensured that the plants are procured from locally adapted seed sources. Biologists, botanists and ecologists can help guide the sourcing and selection of plant material. Nurseries that specialize in native plants should be contacted to source material.

Natural processes

A plant community is not a static entity; rather it is always growing and changing in response to natural processes and disturbance events. When utilizing a plant community as an analogue for design, it is essential to understand the role of agents that affect the composition of the plant community over time. Designers and managers may need to mimic or compensate for the natural processes in a management plan. Consideration should be given for the impact of natural processes and disturbances to the long term vision of the LID landscape design. Natural ecosystems develop and are maintained through natural changes such as the onset of shading, and disturbance events such as:

• Seasonal storm events / flooding outside the design norms
• Prolonged drought
• Microclimate change and progression - sun / shade / moisture
• Plant competition, successional growth, invasive behaviour
• Weeds entering from other sources
• Herbivory
• Pests and diseases
• Changes in soil chemistry / nutrients
• Development of soil structure
• Maturation and decline of plants

External resources

Organization	Coverage	Types of Material	Website
Watersheds Canada	Canada / Ontario	Native Grasses, Ferns, Shrubs, Trees, Vines	https://watersheds.ca/plant-database/
Columbia University, University of Maryland, Smithsonian Institute1	North eastern USA and Canada	Native and non-native trees and shrubs	http://leafsnap.com/species/
Louisiana State University	USA	Grasses, Ferns, Herbaceous, Shrubs, Trees, Vines, Ornamental	http://onlineplantguide.com/Index.aspx
United States Department of Agriculture	USA	Grasses, Ferns, Herbaceous, Shrubs, Trees, Vines, Ornamental	https://plants.usda.gov/java/

1. Leafsnap is an on-line field guide, available as a free mobile app that uses visual recognition software to help identify tree species from photos of their leaves, flowers and fruits.

See Also

• Planting design
• Plant selection
• Bioretention
• Bioswales
• Enhanced grass swales
• Green roofs
• Rain gardens
• Stormwater planters
• Stormwater tree trenches
• Swales
• Vegetated filter strips
• Wetlands

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Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A perforated pipe used to assist the draining of soils.

Defined as those plants (including grasses, herbaceous species, shrubs, vines and trees) that have historically existed within a particular area. Native plants have co-evolved with the local ecosystems and natural processes.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Any form of rain or snow.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Sustainable Technologies Evaluation Program

A parameter that describes the capability of a medium to transmit water.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

Refers to a system that when full, stormwater will bypass the practice. Offline systems use flow splitters or bypass channels that only allow the water quality volume to enter the facility. This may be achieved with a pipe, weir, or curb opening sized for the target flow, but in conjunction, create a bypass channel so that higher flows do not pass over the surface of the filter bed.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Plant species (or non-native species) are those that do not naturally or historically occur in a particular area.

Defined as those plants (including grasses, herbaceous species, shrubs, vines and trees) that have historically existed within a particular area. Native plants have co-evolved with the local ecosystems and natural processes.

Typically non-native plants that out-compete native species. These species lack natural predators, grow aggressively and reproduce rapidly and can be problematic in the natural environment.

Plant species (or non-native species) are those that do not naturally or historically occur in a particular area.