A garden thrives – between a rock and a hard place

A 'living wall' at Powell Gardens near Kansas City is filled with plants.

Peeking out of cracks in a long wall winding along a garden pathway are magenta miniature carnations, phlox with delicate pink blossoms, rosettes of hen and chicks, and fragrant herbs such as thyme and lavender.

The wall, which started out as a structural feature, has become one of the most talked about highlights at Powell Gardens, located outside Kansas City, Mo. This 600-foot-long “living wall” is the longest in North America and second longest in the world.

Building the wall
The wall was designed and built in 1998, and was one of the first structures completed in the “Island Garden” section of Powell Gardens. Horticulturists realized that a wall was needed to hold back the dirt along a path that meanders through.

The island, formerly a grassy knoll in the rolling landscape, includes a large water garden with spectacular pools containing waterlilies, lotus, iris, cannas, and other water-loving species of flowers. The pools cascade from one into another before finally plunging into the lake surrounding the island.

“We needed to make the main path across the island garden accessible,” says Alan Branhagen, Powell Gardens’ director of horticulture. “We decided to make a dry-stack retaining wall so that we could plant species that like dry [conditions].

“We had no idea it would turn out to be as appealing as it has become,” he adds. “It’s now one of the favorite features. I think that’s because it’s so accessible. The plants are right there along the path. It’s very hands-on, great for kids. Also for people in wheelchairs.”

The wall, with its arid-adapted plants, makes a striking contrast with its juxtaposition with the pools of water containing water-loving plants.

Wallflowers
“We tried a variety of plants in the wall,” says Mr. Branhagen. “Some of them weren’t successful. Many of the alpine plants didn’t make it. Few alpines can take the summers here – they’re too hot and humid,” he explains.

“We now have a good mix, with over 200 species,” he says. “We’re always looking for new things, especially forgotten or under-utilized plants.

“We tuck in a few new things every year. We may add something currently in a trial, or a new plant coming out.”

Today the wall is filled with many varieties of hen and chicks (Sempervivum), sedums, Phlox bifida, santolina, basket-of-gold, horehound, lavender, a variety of asters, many different thymes, and several kinds of dianthus.

Plantings include the 2007 Perennial Plant of the Year, Nepeta ‘Walker’s Low,’ and the 2006 Perennial Plant of the Year, Dianthus gratianopolitanus ‘feuerhexe,’ also called Firewitch, which has a clovelike scent.

Continual color
Plants for the wall were chosen not just to withstand dry conditions, they were selected to provide color throughout the season. The plants were also grouped to provide certain design effects.

The entrance is planted with pink, orange, and burgundy flowers, while the next section contains plants with scarlet and blue flowers.

Plants in the center of the wall by the pools contain “Monet colors,” while plants with prairie colors are planted on the east end just before the bridge that takes one to the actual prairie. The arbor area contains soft yellows and blues.

Even the stones in the wall were chosen for their color. “We decided to use limestone from the northeast corner of Oklahoma,” says Branhagen. “They have a warm color, and don’t reflect the sun as much. We didn’t want white stones – they’re too bright and hard to look at in summer.”

Do try this at home
Branhagen says a living wall is not hard for home gardeners to create in their own yards. He suggests setting each layer of stone back one-half inch and not building the wall higher than four feet, unless an engineer is consulted.

The key to a living wall is good drainage, so he suggests adding gravel in back of the wall and including drainage tiles every six feet, to drain the water from behind and underneath the wall.

For the soil, Branhagen uses a mix of one-third soil, one-third crushed gravel, and one-third compost. He recommends planting in early spring to give the plants time to get established and root in before hot weather.

A part of the whole
The wall is only one of the attractions of the 915-acre Powell Gardens. Visitors also enjoy perennial gardens, rock and waterfall gardens, a fountain garden, a meadow, a 3.5-mile nature trail, a conservatory, and many other floral displays. Currently under construction is the Heartland Harvest Garden – opening in 2009 – in which some of the beds, all containing edible plants, will be planted in quilt patterns.

While the gardens have many beautiful areas, the “living wall” remains a favorite. “To me, its appeal is that it’s just so accessible to everybody,” says Branhagen. “You don’t need to get down on your hands and knees to see the plants.”