Submitted by blazej on Mon, 11/05/2018 - 10:57
Mike Smedley

IN THE GARDEN, as in life, things seldom go according to plan.

Such was the case on a partly cloudy Saturday afternoon in July 2008. My wife, Amy, jokes that it was the weekend we went out to buy a new ankle brace but came home with an old house.

You can blame it on a garden that wasn’t there. In fact, there was very little there on the spacious corner lot in Durango, Colorado. A motley amalgamation of bindweed-infested grasses formed a formidable green moat around the small Victorian house. Much-abused trees flanked its front corners: a deer-pruned arborvitae on one and drought-stressed willow on the other. Not only was that willow weeping in form but also in function, as aphid honeydew misted anything beneath its dolorous canopy. In the backyard, a coppiced and cankerous cherry tree looked as if it could simultaneously qualify for disability and survivor benefits.

A few old-school shrubs – forlorn forsythia, neglected lilac and a spiraea of dubious heritage – were scattered hither and thither. Meanwhile, two random yellow currants proved that passing birds served as the yard's at-large horticultural designers.

What did thrive, between a stop sign and utility pole, was a stand of native rabbitbrush baked by the harsh sun and looking like it just didn't give a damn. 

In other words, the property was perfect. 

Durango occupies a peculiar geography. Post a map of Colorado on the wall and Durango would be the thumbtack near the lower left corner.

In a glaciated river valley at 6,512 feet (1984 m), it’s where mountains meet desert. Sometimes that geological how-de-do can be a cordial handshake. Typically, though, it’s an abrupt and jarring collision, like two surly drunks bumping into each other and spilling their drinks at a cocktail party.

Drive 50 miles (80 km) north of Durango, and you'll be ensconced in alpine tundra, where visitors experience shortness of breath at 11,000 feet (3350 m). Sometimes, that’s all anyone experiences above timberline, as noted some 68 years ago in the Bulletin of the American Rock Garden Society, the precursor to this journal.

In the May-June 1950 edition, Dr. C. R. Worth of Groton, New York, reported: "In the southwestern part of the state, the highway from Ouray to Durango climbs well into the alpine zone, but is very definitely not a road for nervous drivers. Good and rare plants are reported. However, when I have been in the region, rains have been almost incessant, and I have not been tempted to do much exploring, nor have I turned up anything of note."

Too bad the good doctor didn’t travel south of Durango, where precipitation can be as spare as the landscape. The ash-grey badlands of northern New Mexico will also take your breath away, but not due to elevation. The high desert’s stark, eroded beauty, a mile and a half (2.4 km) lower than the peaks on the far northern horizon, seems an impossible counterpoint to the San Juan Mountains.

You’d think it would be easy to be the proud owner of a nearly blank-slate property surrounded by natural rock-garden inspiration. But first, Amy and I had a few chores to do around the house, namely gutting it. Everything went into Dumpsters: all the drywall and plaster, 11 layers of linoleum, Eisenhower-era electrical wiring and plumbing that went uphill. We ripped it down to the studs. 

Good news, homeowners! You get to remodel the house over the next couple of years. Bad news, gardeners! You will run out of time, money and energy. Given this harsh reality, what does any obsessive plant-slinger do? Get something, anything, into the ground if only to mark your new territory.

Thus, in the narrow south-facing side yard of the yet-to-be-imagined horizontal rock garden, two skinny Scots pines (Pinus sylvestris 'Fastigiata’) and a columnar blue spruce (Picea pungens 'Fastigiata') were procured and summarily kerplunked.

Winter arrived early, requiring a shift in landscaping priorities for the following summer.  The 100-foot (30 m), fenced-in barrens on the opposite side of the house (we called it “the Prison Yard”) needed rocks. Lots of rocks. 

Not having paved surfaces is a problem in snow country. The protracted mud season called “springtime” provides weeks-long opportunities to ruin every pair of shoes you own.  And so it was at our yard’s new low spot, now directly in front of our new side entrance. Each night, break-your-neck ice formed across the surface. By afternoon, the melted muck could rival the La Brea Tar Pits. The solution was five tons of tawny Great Basin flagstone, professionally installed as a tightly fitted pathway and side courtyard.  While not technically a “rock garden,” the area became a garden. And it had rocks. Close enough.

A large kitchen window looks out over the space, and evergreens were a must –  because Durango only gets a paltry 110 frost-free days per year. The drooping arms of a Norway spruce (Picea abies 'Pendula') and weeping blue atlas cedar (Cedrus atlantica 'Glauca Pendula') accentuate the upright form of a curl-leaf mountain mahogany (Cercocarpus ledifolius) and white-frosted needles of a Horstmann's Silberlocke Korean fir (Abies koreana 'Horstmann's Silberlocke').

At their feet grow holly-like creeping Oregon grape (Mahonia repens) and a duo of hardy manzanitas: the common small-leaf kinnikinnick  ‘Massachusetts’ (Arctostaphylos uva-ursi ‘Massachusetts’) and a western native hybrid ‘Ponchito’ (Arctostaphylos x coloradoensis ‘Ponchito’). A Hillside Creeper Scots pine (Pinus sylvestris 'Hillside Creeper') and the red-cone-tipped Pusch Norway spruce (Picea abies 'Pusch') provide texture. At the fence line, two Pacific Northwest arborvitaes (Thuja spp.) have no business growing but somehow endure the abuse of southwest Colorado’s winter sun. In the meantime, a pencil-thin Woodward juniper (Juniperus scopulorum ‘Woodward’) provides a grey-green exclamation point.

Late spring offers great latitude for clashing colors, and so the orange-chartreuse of Angelina stonecrop (Sedum rupestre) dukes it out with turquoise-magenta of Firewitch dianthus (Dianthus gratianopolitanus). Meanwhile, only a snob would pooh-pooh the buttery yellow and fresh green striped foliage of variegated iris (Iris pallida 'Aurea Variegata'), topped with blue flowers that smell exactly like grape soda.

Taming the edges of flagstone, sturdy ground covers thrive, including tiny-leaf Wyoming native McClintock pussytoes (Antennaria parvifolia), wooly thyme (Thymus pseudolanuginosus) and its aptly named cousin juniper-leaf thyme (Thymus neiceffii). 

Nearby, glossy evergreen spreads of Turkish veronica (Veronica liwanensis) spill forth. Farther on, in a protected nook, a dainty fleabane holds its own; the rare Erigeron scopulinus, sold at select rock garden nurseries, is a demure wildling found only in scattered spots in mountainous northern Arizona.

Imagine the thrill for this rock gardener on the inaugural visit to the North Rim of the Grand Canyon a few years ago. Amidst the regal majesty of the Cape Royal Trail, an inconspicuous patch of Erigeron scopulinus toughed it out on decomposed Kaibab limestone, a treasure growing in plain sight. In my Durango garden, I can revisit that remote outpost with a mere downward glance.

A flagstone project, like Thanksgiving dinner, offers tremendous leftovers. So the horizontal rock garden began with remnants, castaways, and culls from the previous installation, supplemented by large new slabs of greyish Rio Grande flagstone. It also relied heavily on motivation and brilliance of two notable champions of technique and setting.

The ever-undaunted Lauren Springer Ogden devoted a chapter to flagstone gardening in her classic and treasured book Passionate Gardening, co-authored by Rob Proctor (2000, Fulcrum Publishing). I reread the “Gardening Between Flagstone” chapter countless times over the years, practically memorizing Lauren’s plant list and dreaming of a time when I could be, as she perfectly described it, “performing a bit of hopscotch” to avoid trampling a tapestry of mat- and mound-forming gems. Passionate Gardening is the timeless book that kindled my gardening obsession at the start of the millennium.

Meanwhile, the indefatigable Marcia Tatroe took horizontal rock gardening to an extreme. She and her husband, Randy (longtime president of the NARGS Rocky Mountains chapter), smothered their lawn with flagstone and created an astonishing horticultural showcase. In her must-read Cutting Edge Gardening in the Intermountain West (2007, Johnson Books), Marcia wryly recounts the initial stages of the project in which a sea of flagstone smothered dead or dying turf: “It was at this point that one of my son’s friends commented that our creation had all of the charm of a ‘direct nuclear hit’.” 

If you don’t own these two indispensable books, please add them to your library. They motivate, inform, and amuse with each reading. Both signed copies are two possessions I’d rush into a burning house to rescue.

A properly constructed flagstone path or patio typically needs a solid base. Below grade, six inches (15 cm) of dampened, compacted crusher fines (also called rock dust) form a concrete-like but draining layer. Two inches (5 cm) of sand come next. Then well trimmed flagstone is set and leveled. It makes for a handsome hardscape and a foil for surrounding flora. But a planting bed it’s not.

If one desires the exuberance of a horizontal rock garden, place flagstone directly on the ground. This admonition should prompt horrified gasps in some areas of the country, except in the Mountain Time zone.

Here in the Rockies, we deal with ludicrous extremes. Droughts end with torrential rains. Snow arrives in feet, not inches.  A day’s temperature swings 50ºF (28ºC), and no one notices or cares. Then there's hail the size of canned hams. (Not really, but it certainly seems like it.)

What we don’t have is frost heave, the seasonal convulsions so typical to the Midwest or Northeast.  In the Intermountain West, gardeners can easily set flagstone in soil.

The grunt work is straightforward. First, stage slabs across the yard, much like a butler would set out clothing on a bed. (Does anyone have a butler?) Select the rocks that look like they would make the best fit and temporarily set them in situ. Then make adjustments. It’s basically solving an extraordinarily heavy puzzle.

With a trowel, draw around the border of each flagstone slab. Lift the rock and put it aside. Then scoop out or add soil so the reset slabs are an inch above grade. This offers a retaining rim for the eventual post-planting gravel mulch. Jostle the flagstone back and forth to settle. Backfill to eliminate air pockets or scrape off more soil if the slab sits too high or wobbles. Check your progress with a long construction level or a piece of scrap lumber with a smaller level taped to it.

I kept most flagstone gaps to about three inches (7.6 cm). It’s not because there’s some sort of standard spacing; it’s because plants come in 2.5-inch (6.3 cm) black pots. Size doesn’t really matter after a year anyway. Most plants, ground covers in particular, will fill in. Besides, consistency is overrated and “symmetry is for the weak,” as a snarky designer friend once observed.

Larger gaps will look better on the margins of your path. Indeed, an occasional dessert-plate-size opening can be home to a bold tuft of ornamental grass such as Blonde Ambition blue grama (Bouteloua gracilis 'Blonde Ambition') or smallish mounding shrub such as Kannah Creek buckwheat, (Eriogonum umbellatum var. aureum ‘Psdowns’). 

Two items make rockwork easier. A sturdy dolly should be your trusty sidekick for moving flagstone around. Meanwhile, for those so inclined, a boombox blaring Stravinsky’s “The Rite of Spring” or a Mahler symphony can inspire the installer as well as repel curious onlookers.

Rock garden plant descriptions resemble the name of an imaginary shyster law firm: "Challenging, Rare, Expensive & Fussy." These plants certainly deserve a place, but not where foot traffic poses a threat. The best choices for a horizontal rock garden are low-growing ground covers that are as beautiful as they are vigorous. With the exception of succulents, ground covers can take a bit of perambulatory pounding.

Be forewarned, once established and emboldened by a cool root run, these plants can embark on an invasion, enveloping flagstone inch by inch. A late-winter haircut keeps them in check. I hadn’t planned on that part, once again proving that things seldom go according to plan. 

Groundcover stalwarts for the horizontal rock garden include most members of the veronica and thyme tribes. Sky-blue spring flowering Turkish veronica (Veronica liwanensis) is an amazingly tough character and the perfect companion for a prized patch of golden-edged red Schrenkii tulips (Tulipa schrenkii), also an Anatolia native that dates back to 1600, which puts it front and center for the Tulipomania bubble-burst to come.  As a bonus, Turkish veronica’s persistent glossy leaves turn a rusty red with the kiss of autumn frost.

Also an evergreen spreader from Turkey, thyme-leaf speedwell (Veronica oltensis) thrives on abuse, offering a bright spring display of azure-blue flowers. Meanwhile, wooly speedwell (Veronica pectinata) as the name states, provides a green-grey carpet of evergreen foliage featuring tiny white-eyed cerulean flowers. It, too, forms a resilient, drought-tolerant mat across flagstones.

It was the best of thymes and the worst of thymes. Topping the list is the juniper-leaf variety, Thymus neiceffii, with its vernal explosion of shockingly pink flowers. Out of bloom, it’s just as attractive, with needle-like foliage resembling (surprise!) mini junipers. Keep in mind that this thyme will need a bit more moisture and appreciates a little shade in areas with summertime incineration.  Tiny Elfin thyme (Thymus serpyllum 'Elfin') can have a big impact. It’s an easy-to-grow sun-lover with wee lavender-pink flowers over incredibly small rounded gray-green leaves.

Meanwhile, a wolf in sheep’s clothing, wooly thyme (T. pseudolanuginosus) can swallow flagstone in a season. It’s an ideal plant for fast coverage, but keep the clippers handy when this wooly bully encroaches. I dispatch interloping stems from an area reserved for my diminutive jewels, a row of pinkish-white townsendias, early yellow-blooming buns of draba (Draba rigida v. bryoides), a patch of blue-violet Penstemon davidsonii var. menziesii and hardy euphorbia whose tag might still be in that pot in the garage where I banish labels to be organized “later.”

An alpine form of silver nailwort totally nails it in the Southwest garden with a flat-as-a-tortilla habit. Silver nailwort’s official name is a mouthful, Paronychia kapela subsp. serpyllifolia. The evergreen mat takes on a silver cast from profuse whitish seedheads in early summer. Paronychia comes from the Pyrenees Mountains of southern Europe.

On the opposite side of the world, South African natives provide bold textures and exotic colors for the horizontal rock garden.  Though it can spread to 24 inches, vigorous Cotula ‘Tiffindell Gold’ should find a home to roam, perhaps on the side of your flagstone path or in a big gap. This plant, introduced by High Country Gardens, features bright evergreen feathery foliage, deep roots, and interesting golden button flowers held high on thin, four-inch stems. Like bossy thymes and veronicas, it can be kept in check with judicious pruning as needed. It can also tolerate light foot traffic. 

Ice plants (Delosperma), on the other hand, cannot take so much as one errant step. But that doesn't mean squish-prone succulents don't deserve a place in the cracks of a pathway. Just plant them out of harm's way on the margins or flanks of large piece of flagstone with plenty of room.

The most outrageous delosperma offering is the recently introduced 'Fire Spinner', with triple-tone flowers of orange, red and lavender. Not for the timorous or meek, this Plant Select® winner looks impossibly vibrant. Other “good-doing” cold-hardy ice plants include scarlet 'Red Mountain Flame', the classic bright yellow D. nubiginum, salmon-pink 'Mesa Verde', or D. ‘Kelaidis’ named in honor of Panayoti Kelaidis. During a lunchtime visit here in late 2011, Panayoti confidently envisioned a verdant space and reassured that the lot offered huge potential, despite the fact that the "garden" (more like "embarrassing moonscape") was merely a theoretical concept stuck in a self-inflicted purgatory. 

Grey is the new black, and McClintock pussytoes make a handsome pairing with ruddy Hens and Chicks (Sempervivum spp.), their cobweb cousins (S. arachnoideum) and lookalike denizens of the Central Asian steppes Orostachys spinosa.  Though saxifrages resemble semps, they are impossible to grow here, given the alkaline clay soil. Instead, Scarlet monardella (Monardella macrantha 'Marian Sampson') defies the USDA hardiness zones and blooms bright red in dappled sunlight beneath the columnar evergreens.

Some rock gardeners have the magic touch with emerald green Arenaria ‘Wallowa Mountain’, a newish “desert moss” from Oregon. I am absent from that roll call. I must have killed an entire flat of the stuff, but a few survivors are slowly spreading across the flagstone. Afternoon shade seems to be the secret. That, and not roughing up the tiny-haired root balls as I do with most plants during their tough-love introduction to the garden.

Besides 'Fire Spinner' ice plant, two other specimens wow the crowds during a garden tour. The uninitiated don’t know what to make of the reptilian foliage of Bukiniczia cabulica, other than to appreciate its weird mottling. Meanwhile, the fragrant mounding Alpine Blue Mint Bush (Zizophora clinopodioides 'Alpinum') attracts as many bees as it does jealous gardeners who want the tiny bush’s small lavender-blue flowers and heavenly scent for a special, sunny niche. A tip o’ the cap to Mike Kintgen of Denver Botanic Gardens for collecting seeds of this Moroccan treasure.

Rock gardens need a few upright plants, especially in a horizontal rock garden. At eight inches (20 cm) tall, blue bunches of ‘Sea Urchin’ fescue (Festuca ovina v. glauca ‘Sea Urchin’ ) practically towers over its mat-forming neighbors. Yellow dwarf iris (Iris pumila) establishes a dainty 4-inch (10-cm) grass-like verticality. Meanwhile, spreading clumps of small joint fir (Ephedra regeliana) brighten the path with scraggly upright evergreen twigs.

Now that the horizontal rock garden is in maintenance mode, the next challenge beckons, as another three tons of flagstone sit on pallets along the back fence. This summer, those slabs will be installed as a path bisecting a dark-rust, coffin-shaped boulder. I won the behemoth from my favorite nursery during a “Guess the Weight of This Rock” fund-raiser. My estimation was 16 ounces (450 grams) off the rock’s 1,561-pound (700 kg) bulk. Rock gardeners really have an unfair advantage in these contests.

The new flagstone path will incorporate that lucky boulder skirting the perimeter of an established waterwise lawn of buffalo grass (Buchloe dactyloides 'Legacy'). The area practically begs for a xeric border of eriogonums, penstemons, artemesias or most anything successfully trialed at our marvelous Durango Botanical Society demonstration gardens that thrives between the nearby Animas River and our public library.

The plan calls for a calico mix of regional rock: smallish tan chunks of Great Basin flagstone complemented by large grey pieces of Rio Grande flagstone and all interspersed with their deep amber Sante Fe counterparts.

It's an excellent plan. I'm sure I'll be sticking to it. What could go wrong?