A variety of trees, shrubs, grasses, perennials, and bulbs is encouraged to achieve a naturalistic planting aesthetic that provides interest throughout the year. Plant selection and design shall be informed by a number of various factors, including, but not limited to:
- Hardiness
- Size
- Soil conditions
- Water requirements
- Light requirements (exposure)
- Urban site tolerances
Trees
- Tree species shall be selected based on local availability, aesthetic value, and maintenance.
- Utilize tree species as recommended by the Landscape Ordinance.
- Coordinate plant selection and planting timing with the City of Chicago Bureau of Forestry and the Chicago Department of Transportation.
Shrubs
- A combination of deciduous and evergreen, native and adapted shrubs are encouraged for year-round interest, habitat enhancement, and reduced maintenance responsibilities.
- In areas where safety and visibility are key considerations, select shrub species with a mature height of 30 inches or lower for safety.
Perennials, grasses, groundcovers, and bulbs
- The use of native and adapted ornamental grasses, perennials, low mow grasses, groundcovers, and bulbs are encouraged throughout the planting design for year-round interest, wildlife habitat enhancement, and to reduce maintenance needs.
- The use of maintenance-intensive perennials shall be limited to accent plantings or focal areas.
Rainwater Management Features
- Plant selections at or adjacent to rainwater management features (e.g. rain gardens, bioswales, etc.) shall be considerate of the function of those features so as not to impede its capacity to convey or infiltrate rainwater.
- Select native and/or adapted plant species which are adaptable and can tolerate both times of flood and drought.
- Consider that low points of rain gardens or swales may experience short durations of inundation during or after rain events, but may also experience periods of drought during summer months.
Hardiness Zones
- A hardiness zone is a geographically defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone.
- The USDA Hardiness Zone Map categorizes Chicago as Zone 6a (-15°F to -10°F) and 5b (-10°F to -5°F). With the expectation that temperatures continue to rise, many horticulturists and arborists favor species that thrive toward the southern edge of the hardiness zone and limit species that thrive along the northern edge.
- Be cognizant of project and site-specific microclimates, fine-scale climate variations, such as small heat islands caused by asphalt or cool spots shaded by buildings or mature trees.
Sizing
Design and select plant material with mature plant size in consideration. Consider:
- Scale
- Proximity to buildings
- Overhead, underground, and at-grade utilities
- Maintaining sight lines
- Canopy size and shade to be provided
Soil conditions
- Soil makes the foundation of any successful planting area. Understanding the existing and/or proposed soil type, quality, volume, and moisture is a critical part of the site analysis.
- Soils testing, analysis, and recommendations by a soils scientist and/or laboratory are strongly recommended to ensure that the soils are viable for planting and will not result in poor plant performance and/or failure.
- Chicagoland soils can vary but are often:
- Alkaline
- High in clay
- Heavy metal contaminated
- Have some degree of urban fill in their composition
All four of these may lead to plant failure and shall require replacement with clean, imported planting soil. Well-drained, neutral loams are generally preferred as the basis for most planting soils. The planting soil type, quality, volume, and moisture shall inform the planting selections.
Water requirements
- Select low or medium water-use adapted to the Chicagoland climate and group them according to their water needs (hydrozones).
- Native and locally adapted species are strongly encouraged as they require less water in supplement to rainfall.
- Avoid high water-use species and avoid locating low water-use species adjacent to high water-use species, such as turf grass, which require significantly more water.
- Planting species in compatible groupings will enable more efficient watering.
- Factors that can impact soil moisture include:
- Soil type
- Light exposure
- Topography
- Seasonality
- Microclimates
Thus, proper site analysis is key in understanding soil moisture and selecting and grouping plant material accordingly.
Light requirements
- As with soil moisture, different plants have different requirements for light exposure.
- To thrive, plants need to be planted where they will receive the proper amount of light.
- Consider site and area specific sun/shade patterns to determine the daily amount of exposure (hours of sunlight/shade per day) and select plant material accordingly.
Urban tolerances
Urban sites often present challenging growing conditions in the form of:
- High traffic areas
- High exposure to salts
- Pollution
- Poor soils
- Heavy metal contamination
- Compacted soils
- Poor drainage
- Limited soil volume
- Limited water
Plant selections shall reflect their context, with CPS school grounds often being more challenging scenarios for plants than not. Tough-to-kill, hardy, and adaptable species are encouraged, particularly in those more difficult planting locations.
Refer to Volume 3 Section 1.8.4 Approved Plant Lists for a complete list of permitted plant species and 1.5.1 Rainwater Management & Site Drainage for additional guidelines. Refer to the Bureau of Forestry for removal requirements. All removals within the City of Chicago right-of-way shall be coordinated with the Bureau of Forestry.