Planting design

Rain garden on residential lot in Alton, ON.

Whatever the choice of style, it is essential that the surrounding context is taken into account. While a planting design can have a natural appearance, the landscape should never appear haphazard or messy. The aesthetic goal is to achieve a visual sense of fit and scale with the site. The design should be intentional, appropriate and pleasing to the eye and consider the following:

• Maintain visual interest throughout the seasons
• Use of selective species palate
• Use of one or two species or elements to create an accent
• Consistency in plant placement and spacing; incorporating mass groupings, repeating plant groupings, materials and/or design elements
• Avoid sparsely spaced greenery; the planting beds should be fully vegetated once mature
• Consider habitat attributes of plant material
• Enhanced LID function related to pollutant uptake, temperature mitigation, filtration, and evapotranspiration

To help you select appropriate plants for your site, we've developed tables for graminoids, perennials, shrubs, climbing plants, trees and turf focusing on their suitability for implementing LID practices and their aesthetic appeal.

Basic principles

The basic principles of landscape design that should be considered in the creation of any planting plan, no matter how small, are described below. For projects that don't require a landscape architect, LID proponents may have to engage in small-scale landscape design. Not all of the following principles need to be applied in each case, but a basic understanding of each provides guidance. The manner in which these principles are applied creates a particular aesthetic.

Unity and Simplicity

Unity and simplicity in planting design is essential to create an appealing aesthetic. This can be achieved through repetition and consistency. The landscape associated with an LID practice needs to convey that all parts of the planting design fit together to make a whole. The repetition of groups of plants or the character of elements (ie. height, size, texture, and colour) throughout the landscape design can assist on creating a sense of unity in the landscape.

Whilst repetition is a key element used to achieve unity, it is important not to overuse this technique as the result can become monotonous. A landscape design that employs a variety of species in groupings that are repeated throughout a site assists in achieving unity and interest. In contrast, a design that uses just two or three species repeated throughout the entire LID practice may be monotonous.

There is often one visually dominating item or component in a landscape design. Every other component in the design should then be subordinate to this single, dominating focal point. Properly selecting and setting this one focal point in a view should evoke a feeling of satisfaction and pleasure.

Variety and Rhythm

The subtle varying of contrast in line, form, texture or colour can attract attention to a design without inhibiting the overall unified appearance of the design, particularly if there is a smooth, gradual and progressive change in the design element. If applied sparingly, the result can be an increased attraction to the overall composition. Moreover, the creation of sequence may be achieved by using gradation (e.g. the progressive changing of sizes of components or intensity of textures) or by using fixed repetition (i.e. the repeating of an element on a constant spacing) or by using alteration (i.e. the alternating of contrasting or graded colours and textures). When done successfully, the designer creates a sense of movement or flow through a design.

Grouping/massing

Planting different species as single individuals can create a disjointed and un-natural aesthetic in a landscape design. Plants should be placed into groupings of varied numbers (e.g. groups of 3, 5 or 7) to create a mass, which can create a much greater visual appeal. One way to create a grouping is by beginning with a larger specimen, and then adding smaller species with complementary textures, colours and shapes. To create a seasonal grouping, evergreen species, and species with dormant season distinctiveness (ie. form, height, colour) should be included.

Rain garden at Kenollie Public School in Mississauga, ON.

Balance

Balance must generally equalize the overall impact of each of the different design elements so that a visually harmonious composition results. Balance in a landscape design can be either symmetrical or asymmetrical. A symmetrical design is one that exactly duplicates itself along an axis. The informal nature of many LID practices tends to promote the application of the asymmetrical balance approach. This is achieved through the irregular placement of plant groupings along an imaginary axis so that the resulting mass is balanced.

Scale/proportion

Scale and proportion simply refer to the size of the elements, objects and spaces of the landscape in relation to one another, to the LID site and to its surroundings. While there are no rules dictating how this principle is to be achieved, it is important to consider scale and proportion when designing. The relationship in size between components must b relative, or the result can be a lack of harmony in the design. For example, the placement of a large tree in a stormwater planter would be out of scale for this site condition, while the planting of an individual ornamental flower species may appear insignificant in a bioretention cell. Some plant materials may require management (thinning, pruning) in order to maintain the scale and proportion of the intended design over time.

Colour

Colour animates a landscape design. It is affected by light at different times of the day and changes throughout the seasons. Flowers, fruit, leaves or bark of vegetation contribute to colour variation; in response, the designer should understand the details of the life cycle of the plants to be utilized and include plants that flower at different times of year. Colour theory dictates that warm colours (red, orange, yellow) take prominence in the view, while cool colours (green, blue, violet) recede. Colour also has an emotional impact:

• red = strong
• green = tranquil
• blue = dignified
• violet = sophisticated
• brown = earthy
• gray = somber
• black = serious
• orange = exuberant
• yellow = positive
• white = pure

Colour can be used in developing unity, repetition and balance in a landscape design, and to direct the eye to a focal point, if desired.

Texture

The designer should be aware of the texture of the planting materials specified. An appealing aesthetic can be achieved by contrasting fine textured vegetation, such as grasses, sedges, with coarser texture species. However, in exploring design solutions it is important to understand the distance from which the LID practices will be viewed, and to mass vegetation textures accordingly when applying this element to the design. Using both coniferous and deciduous vegetation helps create visual appeal throughout the seasons.

Rain garden with a decorative trench drain cover in Portland, OR. Photo credit: EmilyBlueGreen.

Line

Straight lines represent clean, more formal organizing elements in a design, and they imply a sense of direction and movement. Curved, organic lines promote a more ‘natural’ aesthetic. In either case, clean and contrived shapes have a greater visual interest than weak shapes or indistinct edges.

Form

Form describes natural shape of an individual plant. The variety of forms include weeping, globular, spreading or columnar. The form of plants should be considered both individually and as they relate in the composition of the design.

Features

Features incorporated into planting designs, such as benches, stones, paths, and works of art, can make LID spaces more aesthetic, enjoyable and multi-functional.

Planting plans and specifications

A qualified landscape architect should prepare documents in coordination with engineering design, including tender documents that encompass site development, soil preparation and earthworks. Plans are prepared on a site-specific basis, incorporating planting layout, species composition and spacing. In addition, landscape plans should include construction details and pertinent notes specifying site supervision, monitoring and maintenance.

Early initiatives and successes are more likely to be public, commercial or industrial applications as there is a higher requirement for landscape professionals to be involved and usually a greater opportunity to control and monitor initiatives. Contracts for LID practices may need to be structured slightly differently than a standard construction contract in order to address the long term function of the LID practice, including provision for an extended warranty period.

• Vegetation must meet Canadian Standards for Nursery Stock, 9th Ed.
• Seed planting is not recommended for low impact development.
• Plants should be container grown, balled and burlapped or wire basket.

Recommended minimum plant sizes for planting

Deciduous Trees	45 mm calliper
Coniferous Trees	175 cm height
Deciduous Shrubs	60 - 80 cm height
Coniferous Shrubs / Broadleaf Evergreens	40 cm height and spread for dwarf type 60 -80 cm height or spread for medium form type 25 cm root ball for spreading form type 80 - 100 cm height for columnar form type
Perennials and grasses	#1 or 1 gal. container stock
Vines	#1 or 1 gal. container and staked

Plant Installation

Planting with plugs, pots, caliper tree or shrub stock or sod is preferable over broadcast seeding approaches. Seeding requires stormwater practices to be kept off-line for a period of time following planting to allow germination and plant establishment to occur, and to be irrigated in the absence of adequate rainfall to ensure success.

Plants should be kept in their containers until they are to be installed, which should take place as soon as possible upon completion of the grading and installation of drainage structures. In addition to the planting plan, plant installation details for herbaceous plants, shrubs and trees should be followed per municipal and landscape industry standards, specifications, and guidelines. Avoid staking unless necessary (ie. vandalism or high wind exposure). If staked, then the ties should be a biodegradable web or burlap and removed after the first growing season. If any plant substitutions are required, then the contractor or contract administrator should defer to the designer or municipal agency to make the substitution.

If broadcast seeding is the chosen planting approach, the practice should be disconnected from the drainage area for the duration of the plant establishment period (e.g., first growing season) and seeded areas should be protected with biodegradable erosion control matting to protect seeds from erosion by wind and water.

See Also

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

---

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

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.

The technique of removing pollutants from runoff as it infiltrates through the soil.

A vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration.

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

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.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

Includes the protection of soil from dislocation by water, wind or other agents.