Use variegated plants to brighten the shady places beneath tall trees.
Repeat colors. For each bed, use plants whose colors are either complementary (opposite on the color wheel) or closely related. Group them throughout the planting.
Blend colors thoughtfully. "Once I get a color in my head, I think about what might go with it," says Lee Neff. "When I became interested in the mahogany flowers of Calycanthus occidentalis, I realized that I liked a number of other plants with red flowers or dark leaves. So I began putting them together in a bed that featured foliage and flower color in red, black, and white."
Repeat textures. To unify plants in beds and borders, repeat foliage textures. "I work harder at texture than color," says Neff. "In a collector's garden, that's critical."
Experiment. Over time, plants have to prove themselves ― both in their ability to compete and to fit in. "I do a lot by trial and error," Neff says. "If something doesn't work, I move it, usually in winter."