A foundation bed is planted for foliage colors and textures near the Smithsonian Castle on the Mall. (Adrian Higgins/The Washington Pos)

Foundation beds serve to hide the ankles of a building, but as decorative gardens in their own right, they tend to fall flat in several key areas.

They are typically too narrow, making it hard to install enough plants to create drama. They are too passive and overly reliant on evergreens. And they too often clash with the color of the structure rather than play to it.

All these pitfalls are avoided in an exemplary display I came across the other day in a space that everyone can enjoy.

The garden is a study in foliage display and color harmonies, in maroons, blues and silver, which play off the brownstone behind it. This particular border needs to be good because it fronts what is probably the most famous brownstone in America, namely the Smithsonian Castle on the Mall.

Located on the castle’s narrow west side, the bed is the creation of Smithsonian gardener Rick Shilling and draws its power from its boldness and design clarity.

Some plants function as specimens, others as fillers or textural foils, and together they establish the principle that the most effective gardens don’t need flowers to succeed. One plant here above all others establishes the garden’s confident tone.

Smithsonian gardener Rick Shilling in the thicket of cotinus stems near the Smithsonian Castle on the Mall in Washington. (Adrian Higgins/The Washington Post)

At the back of the border and along the Norman Revival elevation of the building, Shilling has planted a dozen smoke bush, or cotinus, plants. Here’s the twist: Left alone, they would develop into large shrubs topped with a haze of fluffy blossoms that appear in late spring and remain through the summer. In February, he cuts them back to just a few inches above the ground, and the result is an abundance of whiplike stems spiraled with paddle-shaped leaves. This “coppicing” prevents flowering, but the foliage effect is stunning. For months, the leaves of this standard variety, Royal Purple, maintain their burgundy color. This reverts to green by late summer because of heat and humidity, but while it lasts it seems the perfect complement to the fabric, a red sandstone from Seneca Creek, Md. Moreover, the growth in one season is astonishing; the stems are at least 12 feet high.

Another important player in this plant ensemble is the castor bean, a tender shrub grown here as an annual. Its eventual size after just four months is remarkable, in this garden about 12 feet high and the same across. Its color is deep, flat maroon, and the leaves are large, redolent of a maple’s. The stems are a dark purple. (The beans, it should be noted, are highly toxic.) There are four plants in the garden. There would be many more — seedlings appear in May — but Shilling flags where he wants them and removes the volunteers that don’t fit his plan.

In a particularly effective pairing, ornamental sweet potato vine grows beneath the castor beans, echoing the bigger plant in leaf form and color. He has used a variety named SolarPower Red.

A meadow grass named little blue stem (variety Little Blues) provides another ground cover, as does a silver-blue spreading juniper, Silver Mist. This in turn, is in a dialogue with the Serbian spruce variety Berliner’s Weeper. Another lesson of this garden is the importance of seeking out the right cultivar for the desired effect. Shilling introduced me to another choice conifer, the blue atlas cedar variety named Hortsmann, a semi-dwarf, icy blue and handsomely compact version of what otherwise is a large tree. This one is about five feet high.

Of the fine-textured plants in the garden, none is more architectural than the Yucca rostrata, which forms a globe of silver-gray leaves. There are six at strategic spots in the garden. They grow a little higher each year until they reveal a stubby trunk. Once thought too tender for the Mid-Atlantic, they come through winters all right if in well-drained soil.

“When I did this bed I added a light soil mix,” Shilling said. “And I have a small swale at the back, so it’s very fast-draining soil.”

It is the attention to the soil that has not only allowed all these plants to get through a growing season of absurd amounts of rainfall, but to rise to the occasion, literally. (We are about 20 inches of rain above normal for the year so far.)

Both the cotinus and the castor bean would be a couple of feet shorter in a normal year. The main planting of sweet potato vine sprawls across a large area but consists of only three plants.

Shilling, who cares for other plant beds around the castle and the Freer Gallery of Art, likes that most of the work in his foundation border is in winter, before the demands of the growing season take him elsewhere. During the cold months, he cuts the cotinus stems back, takes out the dead wood on a specimen Japanese maple, cuts back the grasses and prunes out the terminal stems on a shrubby Serbian spruce variety named Expansa. This promotes bushier growth.

Once the garden is set up for the growing year ahead, “this is extremely low-maintenance,” he said. “It takes care of itself.”

Of course “low maintenance” to a professional gardener is a relative term, but the lesson here is that the success of such a garden rests on an understanding of the power of textural compositions and the knowledge and imagination to assemble the required plant palette. Or, to put it more poetically, not every garden needs a flower to blossom.

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