"Reds, yellows, and oranges are vivid and happy; blues are cooling and soothing," says garden designer Lucy Hardiman, whose landscape in Portland, Oregon, is a study in the use of color outdoors.

"Red jumps out, blue retreats, and green is the unifier, the garden's go-anywhere little black dress."

Hardiman knows savvy methods of using colors in the garden to evoke moods, shape space, and put the emphasis on plants. The valuable lessons she has learned along the way can help any gardener plan a lively, engaging environment. As she put together her gardens, Hardiman chose her elements -- from the flowers and foliage to the pots, chairs, decorative accents, and painted trim on her home -- for their distinctive hues and for how they mix with one another. The result? Maximum pizzazz.

Match Warm With Cool

Opposites can be attractive: Use plants and outdoor accents in colors from like-minded families -- or from different ones. The results will boost drama in and add visual interest to your yard or garden, creating destinations for the eye.

In her Pacific Northwest garden, Lucy Hardiman doubles the effect of a blue 'Blaumeise' hydrangea. She echoes the moody but showy shade in an architectural finial, and she sparks it with the contrasting yellow greens of variegated Hakonechloa macra 'Aureola,' which cascades over the lawn. She lends "rhythm and resonance," she says, by repeating the plants and finials elsewhere in the garden.

Connect Garden to Architecture

Some flowers and plants are set near the entrances to Hardiman's house. Their colors mimic -- and in some cases match -- the trim on the building, offering a bridge between man-made and natural elements. The taupe 1892 Queen Anne Victorian house is a neutral backdrop with spicy blue and burgundy accents. Red-flushed 'Silk Road' lilies and blue-flowering Nepeta racemosa 'Walkers Low' echo the two trim colors, uniting architecture and setting. Near another entrance, above, some windmill palms (Trachycarpus fortunei) lift their wild fans among bright splashes of red clematis ('Etoile Violette' and 'Barbara Harrington').

Think of Green as a Neutral

Green is the most companionable color for any outdoor space. It runs through Hardiman's garden, stitching it all together, in plenty of combinations, patterns, and tones. In the western border, on top of a street-side wall of local stone, Dicentra spectabilis 'Gold Heart' and Acanthus mollis 'Hollards Gold' mingle with silver-touched Heuchera americana 'Green Spice.' They're joined by yellow-tinged Elaeagnus pungens 'Variegata' and chartreuse Euphorbia characias ssp. wulfenii under the canopy of a dogwood tree. Even the stone wall, which was built by craftsman Jack Peterson, is tinted green with moss. Bits of red come from Clematis 'Niobe' and Hydrangea 'Preziosa.'

Celebrate the Shades of One Color

Choosing a color you like and seeking out several plants that showcase its varying levels of intensity make a space feel more dynamic, adding texture as tones play off one another.

Seen through an arbor behind Hardiman's house, this garden bed includes a tone-on-tone composition. In it, the designer paired deep-maroon Clematis 'Negritjanka' with the white-and-pink 'Laura' phlox and the red-flecked pink 'Sans Souci' lily. The feathery black-red Sambucus 'Black Lace' adds depth and intrigue among the vivid blooms. The green foliage works with the pinks and reds for a high-contrast effect. "In grouping plants, Hardiman says, "I look at every element -- leaves, stems, petals, anthers, stamens. The smallest detail can bring its neighbors to life."

Rely on Pots and Paving

The tone and shape of containers and walkways can showcase plants and enhance an area's aesthetic. On the color wheel, green adjoins yellow, which adjoins orange; mixing these yields a satisfying color scheme.

Terra-cotta pots draw attention to a "hedge" of boxwood (Buxus sempervirens 'Suffruticosa') topiaries. A background scrim of golden yew (Taxus baccata 'Aurea') picks up the color of the boxwoods new growth. A brick terrace, below, laid by Hardiman's husband, Fred, creates a warm foil for spilling leaves near a fountain. Some are green, such as Japanese anemones and Impatiens balfourii. Others are gold, such as Hosta 'Paul's Glory' and Berberis thunbergii 'Aurea.'