Overview
Plant selection plays a key role in the long-term success of planted GSI design installations. Engaging communities in the plant selection process can help ensure aesthetics—from naturalistic to formal—reflect preferences. Choosing appropriate plants for GSI includes considering the site’s soil and light conditions, moisture conditions, proximity to (and the implication of) nearby infrastructure, size restrictions, utility obstructions above or below the surface, and more. Additionally, both short- and long-term maintenance for these plantings must be considered for planted GSI assets to perform at functional, aesthetic, and regulatory standards.
Outcomes
During plant selection, designers curate the species palette that is chosen for optimal GSI performance at the site scale. The Plant Finder tool, along with various resources provided in this section, can help GSI designers make plant selection decisions.
Recommended Involvement
The below offers broad recommendations for who might be involved in plant selection. As always, evaluate participation in accordance with your specific project.
As part of the plant selection process, collaborative engagement between GSI designers and the community is recommended to guide aesthetics and build project support. This might include visits to existing GSI sites to analyze planting style and species selection, concept presentations by GSI designers, and final design reviews. The Plant Finder tool can be used in community engagement to explore and discern plant preferences that fit the functional needs of a specific site.
To learn more see the Engagement step of the design process.
Technical expertise for plant selection and planting design is recommended to select appropriate GSI plants. While the Plant Finder was designed so that anyone in the planning process can use it to explore plant palette options for GSI design, assistance from landscape designers, landscape architects, and/or horticulturalists with GSI plant expertise is recommended. Their input helps ensure that selected palette options are site appropriate and harmonize in a way that minimizes maintenance. A compliance professional with expertise in local municipal and HOA regulations is helpful to augment local government staff knowledge.
To learn more about professionals and their roles in GSI Design, see Who Might be Involved in GSI Design?
Local governments provide input into plant selection and bring expert guidance on municipal ordinance regulations that can limit the design palette. Regulations may be prescriptive, such as a recommended plant list, or restrictive, such as plant height. Local governments also provide knowledge of the site history, which may inform site condition inputs. They also provide information about initiatives, such as expanding pollinator habitat and civic beautification, that are aligned co-benefits of stormwater management.
To learn more about the stormwater management authority of local government, see Illinois regulations.
Tasks
Evaluate Existing Soil Conditions
Determine the GSI site’s soil texture, structure, and infiltration rates. Many plant species are adapted to specific soil types, for example, clayey, sandy, or acidic soils. Explore the Native Soils page and Resource Library to help determine the implications of soil conditions and use the Plant Finder to identify appropriate species. It is important to note that Illinois Groundwork focuses on native soil conditions rather than engineered soil mixes that are brought to a site.
Analyze Light Conditions and Light Patterns
Notice if the GSI site receives full sun (6+ hours of direct sunlight per day), part sun (3-6 hours of direct sunlight per day), or shade (less than 3 hours of direct sunlight per day). Be aware that site conditions affect light patterns. For example, a wooded area is full sun in early spring but becomes shadier as tree canopies leaf out. Similarly, shade patterns evolve seasonally due to the changing angle of the sun. These kinds of light conditions and patterns narrow down the selection of appropriate plants.
Analyze Moisture Conditions and Moisture Patterns
Plan for areas of the GSI site that will have dry, average, or wet soils. Be aware that wet does not mean wetland conditions. For GSI, wet means hours of stormwater inundation in areas that are otherwise dry. Also, be aware that site configurations affect moisture patterns. For example, knowing how stormwater enters, flows through, and exits the GSI provides information about the moisture pattern. These moisture conditions and patterns will narrow down the selection of applicable plants and determine elements of the planting design.
Determine the Implications of Nearby Infrastructure
Does the GSI site receive stormwater runoff from an urban street, sidewalk, or parking lot? Possible road salt and other contaminants flowing with stormwater into the GSI can affect plant health. Use the Plant Finder to identify appropriate species that have been documented to have some, moderate, or high salt tolerance. Other kinds of nearby infrastructure, such as underground utilities can affect GSI siting.
Identify Planting Design Professionals
Planning by landscape designers, landscape architects, and/or horticulturalists with GSI plant expertise is recommended.
Use the Plant Finder tool
Designers may choose to use Illinois Groundwork’s Plant Finder to select appropriate species before developing a planting plan. This tool will help to identify species for use in specific GSI growing conditions.
Identify Plant Suppliers
For larger GSI installations, suppliers will typically be wholesale operations. Smaller installations might be fine with local nurseries or retail mail orders, depending on plant availability.
Identify Installers
Installers of GSI can range from community volunteers, to local landscaping companies, to large landscape architecture firms. In any case, installers should be expertly trained in GSI installation.
Design with Maintenance in Mind
Successful maintenance begins with careful design. Plant selection and design should aim to minimize stewardship hours. Explore the Illinois Groundwork Resource Library for literature that addresses this approach.
Develop a Maintenance Plan
Develop short- and long-term maintenance plans that account for funding, labor, and skillsets needed to perform GSI plant care tasks. Identify who or what entity will be performing stewardship tasks.
Understand Long-Term Funding
Beyond initial investments, it is important to determine where sustainable funding will come from and how much will be available. This helps ensure the long-term stewardship of a GSI site to keep it functioning at peak performance.