There are principles behind successful execution in every art form and combining plants into beautiful arrangements is every bit as much an art as is music or painting. Entire books are dedicated to the subject of combining plants, but a few general principles can here be delineated which may prove useful.

Eclecticism is the most common sin of beginners, with one of these and one of those.. Whereas this can make an impressive collection of botanical specimens, it will not make a very satisfactory garden.

Some of the most beautiful scenes in nature consist of a massing of a predominant plant gradually giving way to another predominant plant in a natural drift, with an area in which both intermix. If these plants harmonize and or contrast nicely, the result is especially striking. Often this will be with a uniform backdrop and or foreground of some single or thoroughly intermixed planting of another kind which 'sets off' the main focal plantings.

So, defining an area, creating an element or unity with a particular look within the garden, which blends into another element in close harmony or distinct contrast is one key to combining plants.

This look need not be created with only one kind of plant and is often all the more rich and interesting if several plants having strong similarities and some differences are intermixed. A combination I personally enjoy, for example, is variegated ornamental grasses mixed with Iris and variegated Iris, with drifts of variegated Liriope and an occasional daylily. All these are blade-leaved plants and together create a distinctive compositional element while providing variations in detail and in blossom.

Right in the middle of this I might place a variegated Hosta, or run the blade-leaved planting into a planting of Hosta, and I might place a Hydrangea macrophylla Mariesi to the rear of the planting. The variegations all harmonize, relating even the Hosta and Hydrangea to the blade-leaved plants, and the broad leaf of the Hosta and Hydrangea contrasts very well with the foliage of the others.

Which brings us to the central principle: Relationship. What was just described is a planting in which all the plants involved relate to each other through several of their characteristics. If you take any two plants you have, or pictures of them, and put them together you can begin to see what is meant by relationship. Do they do anything together? Do they interact, visually? Does each highlight the qualities of the other or does nothing happen - there is no relationship that you can see?

This is similar in principle to combining colors effectively except that with plants it is more complex because we are working with the overall form, with the texture created by the foliage, with the individual leaves, with leaf color and with flower form and color. But the idea is the same. Is there a relationship? Do the plants work together? If not, then don't put them together.

Delicate leaved plants, such as ferns and Aquiligia can combine well with the rich textures of Taxus, Tsuga and other coniferous evergreens. The blue in the leaf of the Aquiligia blends well with the blue of Taxus, for example, while the wide, soft leaflets contrast beautifully with the needles of the evergreen.

If space allows, conifers, such as hemlock or Thuja can make an excellent backdrop to most any flowering shrub, particularly broadleaved plants such as Rhododendron , Kalmia, Azalea and such. These same conifers also combine well with blade-leaved plants. In smaller areas, Ivy on a fence can also serve as a uniform background against which many plants can be seen to advantage.

Another consideration in designing the shade garden is lightness. A shady garden planted with dense conifers and dark broad leaved evergreens can be forbiddingly somber. Lightness can be introduced through both texture, (ferns, for example), leaf color and with bright blossoms. Variegated leaved plants are also very effective in this respect and there are very many variegated groundcovers, shrubs, trees and perennials available.
White flowering shade plants are also not wanting and these too will add considerable brightness and cheer to a shady site.

As plants relate by foliage, so do they by form. A grouping of globe shaped shrubs may be punctuated by the spire of a conical shrub, for example. Or a low spreading planting may gradually rise into a mounded form, into a taller weeping plant type. What does not work, and this is the same principle as applies to foliage and flower, is a random intermixture of various forms. Again, unity, cohesiveness, is required, with an inter-relatedness between a variety of unities.

Each little grouping of plants - those areas which can be visually taken in from one perspective - should constitute a scene of inter-relating components. For example, the graceful, open branched Enkianthus might overhang an hinoki cypress with perhaps a small drift of Astilbe near by and a low spreading ground cover at the base of it all. The idea is to create, within your well laid out beds, vignettes and little worlds of plants in combination.

One such scene I recently created for a client consists of glossy, dark leaved groundcover, Gaultheria running into a planting of pale and variegated Lamium maculatum, punctuated by a scattering of Iris, overhung by spreading false cypress, and all embraced by the airy branches of variegated Cornus alba. These plants together create a little scene of considerable detail and richness, varied in form, texture and leaf color. Variety is introduced, not by a scattering of elements, but by an interaction of cohesive elements. Note that this combination does not even involve flowers, though Gaultheria produces an attractive berry and has good fall color.

This could go on indefinitely but we have not here space for that. The main point is to design an attractive, experientially enjoyable layout. Within this create unities which contain diversities, and which relate one to another pleasantly through both harmony and contrast. These unities can be created using foliage texture, foliage color, flower color and plant form. Combine plants which have a visible relation to each other, which have a give and take and use plant characteristics to relieve the less pleasant aspects of a shade garden. This is a study, and probably a life long study, but the application of these principles should help in the successful creation of your shade garden.