March 15, 2009
Shape and Form: Plant shape combinations...
Shape and Form:
Plant shape combinations to create year-round interest

By Theresa M. Forte

Repetition of shape is an effective design tool. This spiral conifer at Casa Loma seems to echo the shape and structure in the distance. Exuberant borders retain an air of decorum thanks to clipped hedges, shaped conifers, manicured lawns and stone edging.
Nature constantly changes with the seasons. Garden forms are also dynamic, they continually evolve. A structured border without a good colour scheme will be more successful than an unstructured border that relies on colour for strength. The structured border will carry interest through the quiet months of winter while the border relying solely on colour will have little to offer come winter-time. Evergreens, well-branched trees and specimens such as beech that retain their papery foliage over the winter months become significant elements when the garden can no longer rely on colour alone for interest. Strong structural plants earn their keep by creating a sense of enclosure, they help to block wind and screen out unsightly views.

Modern, informal beds planted with masses of perennials offer a variety of shapes and heights as the seasons evolve. In spring, low splashes of colour are featured among the rosettes of later blooming plants.

As the seasons progress, plants increase in bulk and height, often reaching heights of five to six feet in the case of many perennial grasses. The advantage of perennials over shrubs in such a plan is that many will reach a mature height within a year or two.

Attractive form is worth searching for. It is invaluable when planning a border that will hold interest from season to season. Truly sculptural forms, such as that of a mature Japanese maple, offer such interest that one specimen will be sufficient to anchor a small garden plan.

A well-planned garden effectively blends shape and structure to make the most of a tiny space.

In winter, the bones of the garden are clearly visible. Straight, formal hedges at the Niagara Parks Botanical Gardens create walls that help direct the eye to the allée of trees in the distance The strong geometric pattern of the parterre beds is clearly visible. Note the sculptural quality of the bare upward-reaching branches of the trees and dome-shaped conifers in the distance.

Plant shapes can be formal or informal. Formal shapes are characteristically neat, tidy and symmetrical, ideally growing evenly and retaining their shape over time. Dwarf conifers and pyramidal yews are good examples. Informal shapes often have interesting sculptural growth. A small tree with upwardly sweeping branches will appear very elegant when placed to advantage. The layered branching of Viburnum plicatum and the twisted branches of Corylus avellana ‘Contorta’ are examples of dynamic, informal shapes.

Pruning can transform a shrub with a naturally informal shape into a formal shape. However, with today’s emphasis on lower-maintenance gardens, it seems pointless to include plants that will require frequent trims to retain their desired shape. It would be wiser to include plants with tight branching habits to maintain a strong form with minimum help.

Strong, formal shape adds strength to informal plantings. Consider a traditional herb garden with straight pathways and formal low boxwood hedges enclosing beds of billowing herbs. Without the strong lines, the garden would just be a blur, with no sense of order. Strong form makes informal plantings appear intentional. Contrast creates interest.

Ornamental grasses can be used to set the mood in a garden as well. Graceful arching specimens of Miscanthus or Pennisetum seem more informal than the stern upright forms of the members of the Calamagrostis family.

Ultimate height is a serious consideration when placing a new plant in the border. A tall plant placed incorrectly will spoil the picture. The advantage is that a tall plant can be used as a screen or divider, helping to increase the sense of mystery in the garden. When you cannot see the whole border from one vantage point, you are drawn to explore beyond the screen to see what lies ahead.

Height should also relate to the size of the border, property and buildings. Larger scale plants look more at home on properties with the same proportions. However, a large border should include not only larger scale plants but rather a combination of plants of various sizes planted in large drifts. Changes in height often indicate the passing of the seasons. Perennials and annuals start out short and grow as the seasons pass. This can be used to advantage in the border. A plant that offers little more than a low clump of foliage in the spring will make a good companion for early blooming bulbs. Later in the season, when a cover for the fading foliage of the bulbs is required, the taller plant will do just that. Just look at a combination of daffodils and daylilies for examples.

Successful borders use combinations of rounded, upright, spreading, conical and filler (informal or nondescript) plants. Colour echoes will help to solidify groupings in the border. Too many of any one shape will seem either monotonous (all round) or over-stimulating (all spikes). Avoid these pitfalls by planting in moderation, rounded shapes and filler plants should support spiky plants. Spreaders can be used to effectively carpet the ground below arching shapes, keeping maintenance to a minimum.

Theresa Forte is a garden columnist, photographer and garden consultant based in Niagara Falls, Ont.