BY MARTY ROSS / Kansas City, Missouri, USDA Zone 5
PLACES TO VISIT
Allen Centennial Gardens
620 Babcock Drive Madison, WI 53706 608-262-8406 www.hort.wisc.edu/garden2001
Allen Centennial Gardens, a tiny, two-and-a-half-acre jewel on the University of Wisconsin-Madison campus, has an ambitious and beautiful rock garden exhibiting plants from around the world. A path winds through plantings that represent Japan, the Balkans, the Iberian Peninsula, and the Alps, as well as the high North American plains. It is especially pretty here in early spring. The garden is open every day from dawn to dusk.
The Great Wall
The rock garden at Powell Gardens (east of Kansas City, near Kingsville) is a wall about 600 feet long—a near-vertical face of neatly cut, dry-stacked limestone studded with a growing tapestry of bone-hardy, gravity-defying plants, exposed just about as ruthlessly as they could be to the vagaries and extremes of the Midwestern climate, and to the constant patting and poking of curious visitors.
Limestone outcroppings characterize the Kansas City area, and stone foundations and retaining walls are part of the local architectural vernacular. Powell Gardens’ handsome wall (www.powellgardens.org) reminds visitors that this is an excellent environment for the fascinating art of rock gardening. Hardy succulents hug the wall in dense little colonies that seem to bubble up from deep between the stones, elbowing each other into impossible postures. There are cliff-hangers and cave dwellers: Santolina billows from the face of the rocks like puffs of silvery smoke; little buttonheads of sempervivums and Jovibarba spp. emerge from the shadows of overhangs only a few inches deep. Sedums tumble, jostling for space; tufts of Allium senescens fringe the hard edges of rocks.
The living wall, as it has come to be called by its gardeners and visitors alike, is almost five feet high along most of its meandering length, with predominately east and south exposures. The plants grow in a very lean mixture of gravel, compost, and local soil (one-third each). Caroline Polsley Smith and Lindy Stuerke, the gardeners in charge of the wall, jammed the first plants into the cracks four years ago, using a crowbar, trowels, and their fingers (‘We’re brutal,” Smith says). They start with very small plants, massage the roots into the cracks, and plug a slurry of sphagnum moss mixed with local clay soil around them, to preserve moisture while the plants get their start. March is an ideal time for planting.
The living wall is a garden of marvelous shapes, strange textures, and surprisingly flashy colors. The curiously faceted clusters of sempervivums and succulents are among the most entertaining specimens, but shrubby and herbaceous perennials pack the wall too. Oenothera macrocarpa subsp. incana ‘Silver Blade’ has reseeded itself here and there, its sunny yellow flowers contributing to some rather splashy combinations with Ceratostigma plumbaginoides and the fuzzy gray foliage of Ballota pseudodictamnus. Tufted buns of Dianthus ‘Firewitch’ appear to be happier in the practically soilless wall than they are in flower beds. Salvia ‘Raspberry Delight’ blooms on the wall all summer. In late summer, the tiny, bright orange flowers of Zauschneria spp. look almost like flames among the rocks; Aster oblongifolius bursts into purple profusion in September. Artemisia tridentata shoots up from knee-height; blooms of ornamental oregano dangle down the wall like great tassels.
My own home in Kansas City has high stone foundations. Last year, I dug out a small, very sunny bed under a west-facing wall, filled it with gravel and just a bit of soil, and created a rocky little landscape in which to nestle a few hardy succulents given to me by my cactus-cowboy friends, Deadwood Dave Sierer and Cactus Jack Chaneske. It will take time to develop even a hint of the character and richness of the living wall at Powell Gardens, but I’m off to a nice rocky start. H
Oenothera macrocarpa subsp. incana ‘Silver Blade’
This award-winning plant shimmers against the dark brown limestone in the rock wall at Powell Gardens. It thrives in any well-drained soil in USDA Zones 4-9. The plants grow to about six inches tall and spread about one foot. You can count on a succession of bright yellow flowers from May through the frost. ‘Silver Blade’ was introduced by James Locklear, director of the Nebraska Statewide Arboretum, and was named a Plant Select winner by the Denver Botanic Garden and Colorado State University Cooperative Extension in 1999. Sources, page 88.