Between a rock and a hard place? Try crevice gardening
While crevice gardening is one of the hot trends in the United States, it’s not a new concept.
An 1870 book, “Alpine Flowers for English Gardens” by William Robinson espoused the benefits of growing finicky alpine plants in a crevice or dry-stacked rock wall. Since then, crevice gardening has grown, especially in the Czech Republic, where exciting innovations have been developed.
Inspired by the high elevations and rugged mountains where these plants thrive, these gardens are often built on a slope or raised mound to create a habitat that looks like a natural stone outcrop.
Traditional rock gardens feature boulders and stones placed horizontally. Crevice gardens are a style of rock garden in which a good portion of each stone is buried vertically in the soil. Stones are spaced more tightly than in traditional rock gardens.
Will Ingwersen, a British nurserymanand famed alpine specialist, writes: “The basic rule in building a rock garden is to remember always that the rocks, whether large or small, whether outcropping or bold and continuous arrangement, should look as if they have been there since the beginning of time, and have merely been uncovered by natural erosion of the soil.”
In a crevice garden, the rocks are closely spaced, about an inch or so apart, limiting the amount of soil around the roots of the plants. The deep, narrow channels are filled with loose, free-draining soil consisting of coarse sand, perlite and a small amount of humus with a top dressing of gravel.
Alpine plants grow well in lean and sharply drained soil, making the narrow pockets ideal for their cultural needs.
Many of these hardy, little plants have tap roots that require the deep, fast-draining soil that a crevice garden provides. The rocks channel rain and snow melt down around the deep roots while keeping the soil aroundthe base of the plant dry.
Crevice gardens can be any size — a sidewalk crack or two stones with a plant in the middle can technically be a crevice garden. These specialized gardens are ideal for awkward spots where full-sized plants may not fit. They are also an attractive alternative to a retaining wall. Once established, crevice
gardens require minimal maintenance and generally have fewer weeds due to the drier surface and lean soil.
Beginners should consider starting small with a weatherproof container or trough. Fill the container with a porous soil medium consisting of seven parts coarse sand, one part pumice or perlite, and two parts loam. Mound the soil to onethird of the height of the container, creating a miniature mountain. Depending on the size of the container, you may need only a few rocks. Experiment with the positioning of the rocks until you find a design you like.
Then it is time to plant. Seek out alpine plants considering their form and texture. Good options include dwarf conifers, hens and chicks (Sempervivum spp.), cyclamen, daphne, gentian, dwarf iris and dianthus.
Many of these may be found in nurseries that stock fairy garden plants or at a rock garden society plant sale. The Allegheny Chapter of the North American Rock Garden Society is a good source for exploring this niche of horticulture. Their plant sale is scheduled for May 5 at Soergel Orchards in Wexford.
The popularity of crevice gardens has been fueled by a recent book, “The Crevice Garden: How to Make the Perfect Home for Plants from Rocky Places,” co-authored by Paul Spriggs and Kenton Seth (Filbert Press, $39.95).
Spriggs, who lives in Victoria, British Columbia, has been a professional gardener since he was 19 and has melded his passions for gardening and the mountains to become an authority on crevice gardening. Our local rock garden society will be hosting Spriggs at noon March 24 at Beechwood Farms Nature Reserve in Fox Chapel.
He will present two lectures: “Cracks and Crevices” and “My Favorite Crevice Garden Plants.” For details or to register, go to nargspittsburgh.wixsite.
Nancy Knauss is a horticulturalist and a Penn State Master Gardener. This volunteer program supports the outreach mission of Penn State Extension and provides research-based information on best practices in sustainable horticulture and environmental stewardship. Information: alleghenymg@psu.edu or 412482-3476.