Once you have decided your garden’s location and style, it’s time for the part of planning a perennial garden that most people find the most fun: choosing the plants. In designing a perennial garden, you need to consider several specific characteristics of perennials in order to make the best choices. Obviously, the cultural requirements of the plants must match the soil, light, and climatic conditions in your garden. In addition, it is wise to note each plant’s color, height, spread, form, texture, and bloom season. Each of these characteristics plays an important role in the ultimate effect of the garden design.
Perennials come in a vast range of colors. Fortunately, some simple principles of color can help you in selecting flowers and combining their colors in the garden. You’ll find lists of perennials arranged by flower color in Qualities of Perennials.
Red, red-orange, orange, yellow-orange, and yellow are considered “warm” colors; green, blue-green, blue, blue-violet, and violet are “cool” colors. Although colors are neither warm nor cool in a physical sense, they can impart feelings of warmth or coolness, of passion or tranquility.
To the eye, warm colors tend to advance and cool colors tend to recede. When viewed at a distance, warm colors appear closer, and cool colors seem farther away. A planting of predominantly cool-colored flowers—tall spires of dark blue delphiniums, for example—at the rear of your garden makes the yard seem larger. Warm colors, such as a bed of brilliant red and yellow red-hot-poker (Kniphofia uvaria), make it feel smaller. Spot plantings can have similar effects, seeming either to deepen a part of the yard or to bring it closer.
Generally, cool colors are best for close-up viewing and warm colors are better for dramatic displays. Plantings of blue bellflower (Campanula), violet meadow sage, and purple phlox may have substantial impact next to a patio or along a path, but planted in the distance they might be all but lost. To emphasize cool colors, plant them close to the point from which they’ll most often be seen. Warm-color plants such as red daylilies, yellow oxeye (Heliopsis helianthoides), and orange butterfly flower (Asclepias tuberosa), can bring a distant part of the yard into sharp focus. When combining warm and cool colors, keep in mind that warm colors can easily overwhelm the cooler colors.
A hue is a pure color. A tint is lighter than the pure color and a shade is darker. In combining hues, tints, and shades, there are four classic schemes.
Monochromatic color schemes are those with flowers in various tints and shades of one color. No garden is truly monochromatic, of course, because the green of the leaves is always present. Some of the world’s most beautiful gardens have used monochromatic schemes.
Analogous color schemes use colors closely related to one another on the color wheel. Any three adjoining colors are said to be analogous; for example, yellow-orange, yellow, and yellow-green.
Complementary schemes combine colors opposite one another on the color wheel; for example, red and green, yellow and violet, and orange and blue. These are powerful combinations, jarring to some, vibrant to others. They are best with pure colors, rather than shades or tints, for example, scarlet Oriental poppies (Papaver orientale) growing up through dark green bird’s-foot ivy or yellow false-lupine (Thermopsis caroliniana) with blue-violet speedwell (Veronica longifolia‘Blue Peter’).
To soften the effect of strong complementary colors, arrange them to intermingle where the edges meet rather than keeping them in clearly defined clumps. Silver-leaved or white-flowered plants such as wormwood (Artemisia schmidtiana) or baby’s breath (Gypsophila paniculata) soften the impact of bold combinations. Leading up to the brightest colors with flowers of similar color but somewhat less intensity also tones down the impact a bit, for example, combining hot-pink asters with paler pink chrysanthemums.
Polychromatic schemes produce a carnival-like atmosphere in the garden. They may combine any colors and every color. These are often the result of random plantings and can lead to some happy surprises—accidental but especially pleasing color combinations that become the mainstay of the garden for seasons to come.
Foliage color is also a consideration. Perennials have foliage in all shades and tints of green, in blue-green, blue-gray, silvery blue, silvery gray, and gray. Leaves may also be variegated. It’s generally a good idea to avoid plants with variegated foliage. They are notoriously difficult to combine with flowers. Plants with silver or gray foliage, however, have been the pets of many gardeners over the years. Wormwood (Artemisia), lamb’s-ears (Stachys), and mullein (Verbascum) are a few of the silver or gray-foliage plants that are striking combined with flowers. They are especially effective with white or pale blue to lavender flowers.
Perennials range in height from less than a foot to as tall as 12 feet. The standard rule for borders is to stair-step the plantings, with the shortest plants in front, medium-height plants in the middle, and the tallest ones in the back. In island beds of mixed plantings, the tallest flowers need to be toward the center where they don’t obscure the shorter plants. If you follow these rules strictly, however, the result is likely to be too static a combination. Bending rules a bit gives a more natural effect and a prettier garden, as long as the shorter flowers aren’t completely hidden. Lists of perennials arranged by height appear in Qualities of Perennials.
The spread of a plant at maturity is extremely important in garden planning. Unfortunately, it is commonly overlooked by gardeners. Newly planted beds or borders, if planted with the correct spacings between plants, look painfully sparse, with more bare soil than anything else. In the eagerness for a lush, full garden, the natural temptation is to fudge a little (or a lot) and space the young plants closer together than recommended. Although it seems an awful nuisance to look up the spread of each plant and allow for it in your plan, rest assured that if you do not do so, your border or bed will turn into a jungle of scraggly, leggy, rangy plants with disappointingly few flowers. Harsh competition for light, water, and nutrients does not improve the appearance of most ornamental plants. Allowed sufficient room to grow, flowers can grow to their full size and glory.
Plants have their own forms, an important design consideration. For all practical purposes, there are five basic forms in flowering plants: rounded, vertical, open, upright and spreading, and prostrate. Some gardens are composed of only one form, for example, the carefully clipped, rounded forms typical of Japanese gardens; others alternate and repeat certain forms, for example, the traditional English border with its tall vertical spires of blue chimney bellflower (Campanula pyramidalis) behind the rounded forms of white Paris daisy (Chrysanthemum frutescens) edged by low-growing pale blue Carpathian harebell (Campanula carpatica). Many outstanding beds and borders are made up of complementary forms, mixing the rounded with the vertical. If visualizing form doesn’t come easily to you, it helps to imagine the garden in silhouette. Lists of perennials by form appear in Qualities of Perennials.
Although their characteristics are too subtle to play a major role in garden design, you may also want to think about flower forms. The forms that perennial blooms take are too numerous and complex to enumerate here, but some examples are the bell-shaped bellflower (Campanula), daisylike sunflower (Helianthus) or aster, spherical peony (Paeonia), cup-shaped marsh-marigold (Caltha palustris), spurred columbine, frilly or lacy pinks (Dianthus), star-shaped blue-star (Amsonia), and trumpet-shaped daylily (Hemerocallis). Flowers may also be borne singly at the ends of stems, in clusters, or in spikes.
The sunflower family (Compositae) is so large that it’s all too easy to plan a garden with an overabundance of daisy-shaped flowers. The most interesting gardens, like the best bouquets, are those with a variety of different flower shapes. Midnight blue delphinium, white baby’s breath (Gypsophila paniculata), and blue Japanese iris make a striking bouquet and an equally striking combination in the garden.
The term texture refers to the textural appearance of a plant, not the way it feels to the touch. The leaves may be bold, medium, or fine in texture. Texture is determined by such factors as how dense the foliage is, the shape of the plant, and how close the flowers are to one another. For example, texturally speaking, golden groundsel (Ligularia dentara) is bold, peonies medium, and wormwood (Artemisia) fine.
Like color, texture can be used to create spatial illusions in the garden. Bold-textured plants tend to seem closer, whereas plants that are fine-textured tend to recede into the distance. To make the far end of a long, narrow border appear closer, plant bold-textured plants at that end, for example, bear’s-breech (Acanthus mollis). Fine-textured plants make a shallow border appear deeper, for example, wormwood (Artemisia) edging white meadowsweet (Astilbe) backed by white Japanese anemone (Anemone x hybrida) and white goats-beard (Aruncus dioicus). The pale colors of the flowers and the fine texture of the plants both contribute to the illusion of greater depth. A list of perennials especially valuable for textural effects can be found in Qualities of Perennials.