Dainty Plants to Cure the Boulder Blues

Rocks are nature’s acne, some pitting the surface of the earth and others just waiting to erupt. Small rocks are a nuisance, but they are easy to control: sift and dig, dig and sift. A big rock, one that has burst onto the face of the landscape, poses a greater challenge; expensive to remove it is often left to stand alone, unanchored and irrelevant. But a large rock can provide a visual treat if you pack the crevices with soil, plant them with a variety of tiny alpine perennials and create a rock garden oasis.

Alpine plants – a term that once meant the small sub-shrubs that grow above the timberline but today refers to any dwarf or compact rock garden plant – share many of the same characteristics. All are fussy about soil, demanding a well-drained gritty bed that is slightly alkaline. With few exceptions they put on their most spectacular display in the spring, a flower show of pastels – purples, pinks, whites, blues – no shocking colors among the alpines. And, bad news for those of us who toil in woodland gardens, most require full sun, at least 6 to 8 hours a day (not many trees above the timberline), although there are a couple of handsome exceptions that tolerate partial shade.

The first alpine that thrives in light shade, the Dwarf Columbine (Aquilegia flabellata)

bursts forth in early spring with a mass of dainty flowers that look like old-fashioned purple or white bonnets. Blooming a little later than the columbine in early summer, Dalmatian Bellflower (Campanula portenschlagiana)

was first discovered in Croatia, tucked among the limestone outcroppings of the mountains. This little beauty produces a profusion of flaring violet bell-shaped flowers forming a carpet of color from late spring through the summer. Both of these alpines share a love of light shade and well-drained soil.

Of those alpine plants that demand full sun, spring is their season and the selection is vast, forcing choices – choices by color. If you are partial to white, three fine alpine varieties are Candy Tuft (Iberis sempervirens), Wall Rock Cress (Arabis caucasica) and Sandwort (Arenaria montana). Although its peak bloom time is spring, Candy Tuft,
will continue to flower sporadically throughout the summer and into fall, and for a visual punch choose the handsome cultivar ‘Snowflake’ for your rock garden, a variety prized for its glossy green leaves and showy flowers. Another spring bloomer, the old favorite Wall Rock Cress (sometimes known just as Rock Cress)

forms a neat mound of dense gray-green foliage and can spread as much as 18 inches, so give it some room on the rock. One of the loveliest of all the rock garden plants, the trailing Sandwort

is covered in spring with masses of pure white flowers with bright yellow centers, softening the hard edges of a wall when it spills over the side.

One of the first pink alpines to bloom in spring, Sea Thrift (Armeria maritima)

pops up in April its dense round flower heads dancing on slender stems. Thriving in dry soil this plant has staying power; the sturdy Sea Thrift has been in cultivation since the late 16th century. Blooming a little later, Soapwort (Saponaria ocymoides)

gets its common name from its roots which were used by pioneer women in washing clothes; rubbed on clothes they emit a powerful detergent which dissolves grease and dirt. Soapwort blooms through late spring into early summer and makes a dramatic display when draped over the top of a rock. To add some fragrance to your garden, choose Cheddar Pinks (Dianthus gratianopolitanus)

deriving its common name not from the cheese but from its original home the limestone cliffs of Cheddar Gorge in England. The hybrid ‘Tiny Rubies’ blooms a vibrant pink and, if you deadhead diligently, it will continue to flower into fall. For a tough vigorous evergreen groundcover that can handle kid traffic, Mother of Thyme (Thymus serpyllum)

emits the familiar scent of the herb when crushed under foot. Another member of the family that deserves a spot in any rock garden is Creeping Thyme (Thymus praecox),

a perennial that is covered with pink flowers throughout the summer. Like its cousin Mother of Thyme, Creeping Thyme is associated with strength, courage, happiness and wellbeing (who can resist a plant with such a pedigree?). If you still have a spare spot for yet another pink alpine consider the late-blooming Stonecrop (Sedum seiboldii).

Although it is covered with dusty pink blossoms in the fall, it is the fleshy foliage that commands attention; its blue-gray leaves edged with red during the growing season turn brilliant copper in the fall setting a rock or wall ablaze. This is a great choice for a hot dry spot.

If pink is not your color there are several purple or blue alpines to choose from, and the Mediterranean Rock Cress (Aubrieta deltoidea)

is one of the earliest to flower. Named for a French botanical artist this Rock Cress is easy to grow, thriving on benign neglect; just give it a hot dry space and watch it flourish. Two excellent hybrids are the deep blue ‘Novalis Blue’ and ‘Rokey’s Purple’ which is covered with rich purple flowers all season. Another rich purple alpine to consider is Sprawling Speedwell (Veronica prostrata)

that forms a mossy mat 4 inches high and is covered with clusters of intense blue flowers from late spring into early summer. To tone down the intensity of all that purple, bathe your rock or wall with the bright yellow flowers of Basket of Gold (Aurinia saxatilis),

or if that color is too sharp for your taste, choose the soft lemon yellow variety ‘Citrina’.

So, if you are faced with a naked boulder or a bare wall that screams “boring!” forget the jackhammer and work with nature. Pack the dips and gullies of your rock with mounds of soil and plant a variety of small alpines and transform a barren eyesore into a miniature garden. Or if your challenge is an imposing rock wall, stuff the chinks and crevices with a some soil and trailing alpine plants, letting them spill out over the sides of the wall, softening its stony face with a mass of pastel flowers. Alpine plants won’t cure nature’s acne, but like any good makeup they can help in masking her flaws.

Plant Sources

Wrightman Alpine Nurseries
www.wrightmanalpines.com

High Country Gardens
www.highcountrygardens.com

Blue Stone Perennials
www.bluestoneperennials.com

Photo Credits

Aquilegia flabellata – Ghislain 118
Campanula portenschlagiana – Wouter Hagens
Iberis sempervirens – Heron2
Arabia caucasica – H. Zell
Arenaria montana – Mtiffany71
Armeria maritima – Wilson44691
Saponaria ocymoides – Tigerente
Dianthus gratianapolitanus – Kurt Stuber
Thymus serpyllum – Jerzy Opiola
Thymus praecox – Marek Slusarczyk
Sedum sieboldii – Digigalos
Aubrieta deltoidea – Stan Shebs
Veronica prostrata – Hans Hillewaert
Aurinia saxitilis – CC BY-SA 3.0