A split-complement color scheme employs three equally spaced colors from the wheel, and in this case (with a little horticultural liberty) rose red Rosa ‘American Pillar’; the long-blooming lavender-blue Clematis ‘Betty Corning’; and greens including chartreuse Cotinus coggygria ‘Golden Spirit’.

A variation on the complementary scheme calls for adding the adjacent colors to both sides of one of the complement. This arrangement is known as the split complement. If you chose yellow and its complement, violet, the variation would be yellow with red-violet, violet, and blue-violet.

Another scheme imagines a triangle laid on top of the color wheel. Basically, this triadic scheme uses any three equally spaced colors around the wheel. The attraction of the triadic is that it has an inherent contrast that makes each of the colors look rich, but unlike the sharp and contrasting differences between colors in the complementary scheme, these remain in balance.

The double-complementary, or tetradic arrangement, brings together two pairs of color opposites as if an “X” were drawn across the wheel. Imagine a primary and a secondary color are selected, as well as their complements. The points of the “X” would aim toward the four chosen colors. If the first color were yellow, and the second orange, then the third would be violet and the fourth blue.

These esoteric arrangements probably sound like more than you may want to know, but for combinations in planters or window boxes, some of the schemes can be brilliant. It is probably a useful thought to allow one or two colors to dominate, as is the case with some of the other intricate schemes, and consider an accent of white.

A yellow, red-violet to blue-violet tetradic scheme suggested by nurseryman Tony Avent of Plant Delights stars ‘Picasso’ calla lily and chartreuse-leaved Buddleia ‘Evil Ways’* introduced by another nurseryman, Sean Hogan of Cistus Nursery. To these, we added (clockwise from left) a hosta stem with blue-violet buds, a plume from the dwarf Astilbe chinensis ‘Pumila’, yellow Thunbergia alata ‘Sunny Lemon Star’, pink Monarda fistulosa above Allium thunbergii ‘Ozawa’ and Lilium ‘Leslie Woodruff’.

Expert gardener Charles Cresson has a border backed by a white picket fence made of recycled plastic and planted in what could be considered a triadic scheme, with tones of yellow and two colors—blue-violet and red-orange—one third way around the color wheel.