Planting design

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.
• Consider habitat attributes of plant material
• Enhanced LID function related to pollutant uptake, temperature mitigation, filtration, and evapotranspiration

Basic Principles

The basic principles of landscape design that should be considered in the creation of any planting plan are described below. Not all need to be applied in each case, but a basic understanding provides guidance for the designer. The manner in which these principles are applied creates a particular aesthetic.

Unity/Simplicity - A degree of unity and simplicity in a 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.

Repetition/Rhythm - Repetition is the key element used to achieve unity. However, 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 utilizes two or three species which are repeated throughout the entire LID practice may be monotonous.

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 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.

Balance - 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 of the landscape in relation to one another and the site. While there are no rules dictating how this principle is to be achieved, it is important to consider scale and proportion when designing. 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 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. Colour theory dictates that warm colours (red, orange, yellow) take prominence in the view, while cool colours (green, blue, violet) recede. 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 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.

Line - Straight lines represent more formal organizing elements in a design and 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.

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Planting Plans and Specifications

For professional projects that are, beyond the scope of a simple homeowner designed and constructed rain garden, the consultant must prepare planting details and specifications that reflect the specific municipal and agency requirements. 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 securities and an extended warranty period.

Plant Installation - Plantings should be installed 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.

See Also

• Bioretention cells
• Swales
• Bioswales

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.

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

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