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Artistic perennial combinations
Perennials present high-level design challenge

A palatte of gentle pastels and soft textures creates a soothing mood in this perennial border found in the Laking Garden at the Royal Botanical Gardens in Burlington, Ont.
The art of combining perennials can take a lifetime to perfect. Despite an abundance of well-researched and thoughtful books on the subject, it is a skill that remains elusive to many professionals and hobby gardeners. To effectively paint a truly pleasing picture with perennials, the expertise of several disciplines must be combined, along with an intuitive sense of design.

The designer must understand the micro-climate and soil conditions of the planting space, including light, wind, soil fertility, tilth and available moisture. The planting must be appropriate to the scale of the space, in addition to satisfying the reason for the planting, such as creating a focal point or its use in creating a lively or soothing atmosphere. In addition, the clients' preferences must be taken into consideration. With all of these conditions understood, the designer can draw up appropriate plant lists from which compositions can be made. The members of each composition should harmonize with each other and their immediate neighbours to create a pleasing theme. Catherine Ziegler offers a wealth of practical information when it comes to perennial combinations in her book, The Harmonious Garden, Color, Form and Texture. "This final phase of selection and placement warrants a pronounced simplicity. Restraint in the number of different plants used and consistent attention to the correct scale, both in the individual plant group and in its place in the entire landscape, will produce the strongest design."

John Valleau, corporate horticulturist at Valleybrook Gardens in Niagara-on-the-Lake, Ont., offered several practical suggestions. "The best perennial artists make use of some extremely simple tricks. Pick a flower and wander around the garden with it, looking for combinations with other plants that please your eye. It's always best to match up simultaneous combinations (i.e., things that bloom together) as close to home as possible. No book ever written can guarantee that any two plants will flower together in your garden at the same moment. What works in one climate very often does not work in another."

Purple fountain grass (Pennisetum setaceum 'Rubrum') and Cardoon (Cynara cardunculus), make a dramatic, modern composition.

spirea bumalda 'Goldmound' and Nepata 'Dropmore Blue' create a very simple, yet striking combination that will suit a sunny location.

The small burgundy coloured leaves of Berberis are the perfect foil and offer a great colour echo for the markings on the Hemerocallis.
When creating pleasing combinations, colour, form and texture are not equal partners. Our eye is naturally drawn to colour first, then form and finally texture. Texture and form are often overlooked when strong colours dominate the composition.

In a large planting, the texture of an entire plant or group of plants will be required to contribute to a composition. Plants with a fine texture will have little impact when viewed from afar, say, more than 6 m (20 ft.). Medium to large plants displaying a stronger texture will be more effective when viewed from this distance.

When the goal is to rework or plan a small section of a border, Valleau reminds us of a simple technique that Marjorie Mason of Mason Hogue Gardens often recommends. "Within a circle, roughly the diameter of your outstretched arms, aim to include a perennial for spring bloom, one for summer and one for early fall interest." Valleau suggests adding a fourth plant with primarily foliage interest to complete the picture. "This method ensures interest throughout the growing season and it's simple enough to then add in more plants that bloom simultaneously with your basic foundation choices."

Valleau offered a few combinations proven very effective in his own Zone 6, clay-based, primarily shade garden: creeping woodland phlox (Phlox stolonifera) 'Sherwood purple' and leopard's-bane (Doronicum) used as an under planting for May-blooming hardy bulbs. A spring flowering combination of double English primula (P. vulgaris), windflowers (Anemone blanda) and Lamium maculatum have survived in his clay-based garden for many years.

To add early interest to the border, Valleau recommends using plants with excellent emerging dark coloured foliage, including peonies, astilbe and ornamental rhubarb (Rheum palmatum). He adds tree peonies to perennial borders because of their excellent flower form, colour and foliage. As well, he likes to use Allium 'Purple Sensation' for interesting colour, form and texture.

Valleau suggested two of his favourite (and under-used) groundcovers for shade compositions. The first is red-veined sorrel (Rumex sanguineus), which forms a low clump of foliage in moist soil, with each dark green leaf showing an intricate pattern of beet-red veins. The second recommendation addresses a challenging spot under trees that may be dry by mid-summer. Spring vetchling (Lathryrus vernus) will form a low clump in the woodland garden. Light green shoots burst out of the ground in the spring, producing clusters of pea-like flowers in shades of pink to magenta purple. Spring vetchling becomes dormant in summer.

"Remembering that the average perennial has a brief period of bloom, the best kinds of plants in a border are those that have good flowers and attractive foliage," says Valleau. "Once your eye begins to focus on leaves, the diversity is truly amazing. They vary so much in colour, size, shape, fineness or coarseness of texture. Aim to have diversity of foliage and your garden will offer something attractive to look at for months on end."

On the lighter side, Valleau admits to also using a technique we may all have tried in the past: "I have found some great combinations just roaming around the greenhouse. Trays of perennials arranged on the ground, blooming in sequence or interesting foliage combinations just happened to be placed side by side."

Perhaps the best lesson in the end is to be receptive to new combinations whenever they are presented to you, no matter if you're walking around the neighbourhood, touring a garden, looking over rows of plants at a wholesaler or browsing through the pages of your favourite gardening books.

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

Images courtesy Theresa M. Forte and John Valleau

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