Mixed borders are those with more than one class of plant. You may add some bulbs or annuals to a perennial border, or design the border with a strong shrub presence augmented by perennials and bulbs. Although most people think of perennials in connection with flower borders, there are good reasons to add other types of garden plants.
Annuals work well to fill in blank spaces and add extra color. Perennials have the advantage of being permanent additions to the border and of providing a basic framework, but the warm-season annuals undeniably have a longer season of bloom. This fact makes them indispensable for color early in the season before the perennials come into bloom or to succeed those that are past bloom.
Many of the most beautiful flower beds and borders in the world have predominantly perennial plants, but annuals, bulbs, flowering shrubs, and other plants are integral to the total effect. Limiting the choices to perennials exclusively means missing out on such charming combinations as yellow nasturtiums and blue salvia or deep purple heliotrope and dark rose beardtongue (Penstemon). Gertrude Jekyll, in her garden at Munstead Wood, combined scarlet dahlias with Oriental poppies (Papaver orientale), and wake-robin (Trillium grandiflorum) with Solomon’s-seal (Polygonatum) and lily-of-the-valley (Convallaria majalis).
Spring- and summer-flowering bulbs are also important to any flower border, if only for the variety of unusual flower shapes they provide: tulips, hyacinths, cyclamen, scilla, camas, and daffodils of all shapes and sizes are but a few of the spring-blooming bulbs that bring life and color to the border well in advance of most perennial and annual bloom. The midsummer border can be made more interesting by adding tall summer lilies (Amaryllis belladonna) and the dozens of varieties of dahlia and allium.
The greatest drawback to an all-perennial border is that it is bare in winter. Planting a few hardy shrubs or small trees will give you something to look at during the long, dark months of winter, to bear witness that there is indeed a garden under all that snow or sodden soil. Choose shrubs or small trees that won’t outgrow their allotted space, and look for varieties with some interesting fall or winter characteristics, such as bright foliage, berries, or an attractive branch pattern when the plant is bare. Such trees include dwarf forms of crab apple or flowering cherry, Japanese maple, dogwood, or flowering chestnut. The Japanese maple ‘Sangokaku’ has bright red branches that make a dramatic silhouette against snow and gleam brilliantly when rinsed with rain.
Several dogwoods also have colored twigs and branches: Tatarian dogwood (Cornus alba), Siberian dogwood (C. alba‘Sibirica’), and blood-twig dogwood (C. sanguinea) all have red branches for winter color as well as attractive flowers in May and June. Yellow-twig dogwood (C. sanguinea‘Flaviramea’) has yellow twigs and branches. Trim dogwoods back hard after they bloom to get the new growth that gives the best winter color.
Rose-gold pussy willow (Salix gracilistyla) adds early spring interest; you can keep it to size by cutting the branches for arrangements or by pruning it to 2 feet every three or four years. Dwarf hollies, dwarf junipers, and hebe can be incorporated into beds and borders for year-round interest.