Submitted by gsparrow on Fri, 12/07/2018 - 08:08

For over a hundred years, the trough has been the container of choice for rock gardens. The gold standard is the genuine article made of stone and rescued from a farmyard or an old village square. Vintage stone sinks (like the one my mother couldn’t wait to replace with stainless steel in her ranch kitchen in the 1970s) have also traditionally been used as rock garden planters. As antique troughs and sinks have become scarce, reproductions are occasionally available. Like the originals, they are often too heavy and too expensive to be practical for most gardeners. A lucky few can point to their venerable troughs with great pride, the rest of us can only hope for a trough inheritance – and look for alternatives.

 

Whatever their genesis, troughs are ideal for displaying tiny plants that otherwise would be swallowed up and smothered – both figuratively and literally – by larger, more vigorous companions. Elevating these treasures above ground level also positions them at a height more convenient for viewing as well as for easier care and maintenance.

In a trough the gardener has control over every nuance of plant culture. The soil mix can be matched to the inhabitants’ needs in regards to drainage, texture, and pH. (Some plants won’t tolerate your garden’s soil no matter how you amend it.) When light conditions change (as is inevitable as gardens mature) all but the heaviest troughs can be moved to a more suitable location. Customized watering, whether adding more or excluding too much, is not overly burdensome in such a small space. Each winter I relocate several pots of hardy cacti to positions under eaves to keep them dry. Gardeners in wet-winter climates like Portland and Seattle utilize panes of glass or Plexiglas on legs to cover troughs of moisture-sensitive alpines. Gardeners with squirrel and rabbit problems prevent nibbling by covering their troughs with wire cages. Where sub- zero temperatures are routine, it’s a simple matter to cover a trough with a frost blanket or evergreen boughs, either all winter or for the duration of the polar vortex.

Troughs can be quite beautiful. Santa Fe photographer Charles Mann likens them to jewelers’ cases filled with precious gems, each arrangement unique, depending on the gardener’s tastes and whims. Trough gardens generally contain a collection of plants from diverse regions but from similar habitats. Because they tend to come from harsh environments, these plants share physical characteristics (low to the ground in compact mats, buns, or mounds) that make them visually compatible even if actually from origins as far removed as the steppes of Central Asia and the Great Basin of western America. Combined within the frame of a trough the result can be quite satisfying. Encouraging one or two individuals to spill down the sides, as well as injecting tiny trees, pieces of driftwood and ornamental mineral specimens, help effect a naturalistic and harmonious composition.

There is no limit to what imaginative rock gardeners can do with a trough, the only immutable being that plants with like cultural needs (as to water, sunlight and soil) are grouped together and their needs met collectively. Troughs featuring diminutive crevice gardens are currently in vogue. Native plant purists can follow the example of Gwen Moore who, when commissioned to design a trough garden at Denver Botanic Gardens in 2001, collected seeds and rocks from various Colorado habitats to recreate natural landscapes in miniature. A trough is also ideal for displaying dwarf shrubs or a collection of small cacti, and though not my taste, a fairy garden in a trough might inspire a child to a lifelong interest in rock gardening. One trough can stand alone or several may be displayed in a grouping. Whatever the presentation, the trough is so iconic to rock gardens worldwide that it has become emblematic of the serious rock gardener.

I like to think of myself as a serious rock gardener. But, sadly, until quite recently I’d never had much luck with troughs. The first two I tried were table decorations awarded as door prizes. They were quite small and made from hypertufa. Generally undamaged by freeze and thaw cycles, hypertufa is perfectly suited to a climate like mine where winter temperatures routinely fall well below zero degrees Fahrenheit.

Colorado rock gardeners, like gardeners everywhere, also appreciate hypertufa because it is relatively lightweight, easy to work with and porous enough that it’s nearly impossible to overwater if using a fast- draining medium. Where too much moisture is the issue this is all well and good. With fifteen inches of precipitation (in a good year!) and atmos- pheric humidity that frequently measures at less than 10%, too much moisture isn’t usually a consideration in my garden. Because hypertufa dries out so readily, most Colorado rock gardeners water their troughs daily, regardless of the size of the trough or the type of flora it contains. I don’t have automatic irrigation. Dragging a hose out every day is down- right impractical so I use a watering can. The trouble was, if I forgot to water for even one sweltering day in summer, whatever I had interred in these small troughs – no matter how xeric – withered and died. The soil volume of these really small troughs undoubtedly exacerbated the problem.

I eventually lost interest and decided troughs were not for me. It wasn’t until a few years ago that I reconsidered. A monster of a chokecherry on the west side of the house sucks every bit of moisture out of the soil for tens of feet in every direction making it impossible to grow much of anything at its feet (seriously, not even ajuga will grow here). With a garden tour imminent that June, I yet again replanted a bare patch some ten feet by ten feet beneath the chokecherry with “dry shade” recommendations and vowed to be more vigilant with irrigation. One of our sons agreed to come over and water the new bed while my husband Randy and I attended a study weekend a couple of weeks before the tour date. We arrived home to find the entire planting dead. Our son swore he’d watered as instructed – the greedy chokecherry had won again.

A few years previous to this latest failure, I had dropped a half- whisky barrel into a dry spot on the other side of the chokecherry and filled it with shade-loving annuals. With no tree roots to steal the water, these had done well. (Unfortunately whiskey barrels in contact with soil rot rather quickly and when I removed the barrel a few years later I discovered that the chokecherry’s roots had grown up through the drainage holes!) Still, container gardening might be the one and only way to thwart the chokecherry’s demand to be an only child. (If this tree didn’t provide shade to the entire west side of my home in summer I would remove it.)

For some time I’d been admiring large stone troughs called tinajas at a local garden center but just couldn’t imagine where one would fit in our small garden. It was at that point that I realized there was enough bare ground beneath the chokecherry to accommodate a small fleet of these things. I could afford only one at the time, but a large one would go a long way toward filling the void and diverting attention from the sad state of affairs I’d returned home to.

According to Wikipedia, tinaja (pronounced tee-nah ́-hah) is a term originating in the American Southwest for water-holding potholes in bedrock that occur below waterfalls, carved out by spring runoff or seepage, or created by sand and gravel scouring rock in intermittent streambeds. Merriam-Webster’s first definition for tinaja is a large earthenware jug that holds water. With roots in Castilian Spanish for vessel or tank, tinaja has morphed into a moniker for stone troughs from Chihuahua, Mexico. These come in all different shapes and sizes and are widely sold in Colorado nurseries as planters and basins for fountains. Hand-hewn from volcanic ash, tinajas are purportedly porous enough that water will drain through the stone. (I had my doubts so for added insurance, before we set ours into the garden, Randy drilled several holes in the bottom using a masonry bit.) According to importer Big Bend Stone of Terlingua, Texas, tinajas provide good insulation to protect plants in winter as well as evaporative cooling in summer.

I don’t know about that, but mine have developed colonies of mosses and lichens on the exterior as promised. Fortunately, Charles Mann was visiting us the week before the garden tour because installing our tinaja was definitely a two-guy project. Randy and Charles took down a section of the split rail fence that borders the side yard. They then drove our truck into the field adjoining our property, backed up to the garden and dropped the 200-pound tinaja over the flattened chain link fencing that lines the split rail, onto a bale of peat moss (while I stood on the fencing pleading with them to be careful lest they break my treasure. Charles retorted that in his opinion the soft rock would deteriorate quickly in any case).

After they muscled the tinaja into position, I filled it with a common denominator trough-soil mix of 1/3 gravel, 1/3 coarse sand, and 1/3 sandy garden loam, planted a selection of shade-loving rock garden fare and mulched between the plants with stone chips. I then camouflaged the area around the tinaja with flat sandstone paving stones much the same shade of beige as the trough. Bare earth gone, garden tour disaster averted. And as a bonus, beyond simply filling dead air, the tinaja was a perfect fit aesthetically.

For several years prior to the tinaja’s addition I’d been attempting to change the character of this particular area, the goal to make it more naturalistic, less English border. An overhaul of the 70-foot-long walk that transects this garden transformed the meandering path into a dry streambed with boulders along the edge. Formal borders on either side no longer made sense. Nor did level ground. This is a heavily shaded garden and a rocky streambed running through a level “forest” was just plain counterintuitive. I was sitting in a boulder field while Randy hiked St. Mary’s Glacier west of Denver when this epiphany struck. In the shaded spruce and bristlecone pine woods beyond the snowfield’s edge, wildflowers and understory shrubs were tucked up against boulders in ground that was anything but flat. Here was nature’s model. Since that summer, I’ve been gradually adding boulders. To form contours, every time I bring in another boulder I add soil around the base, sculpting the beds into slight hills and swales. I did the same with the tinaja.

As I could afford them I’ve added two tinajas to the side yard garden and three more to other parts of the garden – all “worked into” the garden as if they were freestanding boulders. While truly beautiful, tinajas have not been the panacea I’d hoped. They have not cracked in Colorado’s sub-zero winters as Charles predicted, but the porous rock is no more water-retentive than hypertufa. The free-draining trough
soil mix undoubtedly increases the number of drought-killed plants. Watering more frequently would help but I’ve already proven that my good intentions don’t readily translate into action. A few plants have put up with the extreme dry shade conditions, but not many. Only
Juniperus horizontalis ‘Mother Lode’, Primula marginata and P. allionii selections, several tortured silver saxifrages, Heuchera pulchella, Gentiana verna, Silene zawaskii, and various sedums and sempervivums have persisted for more than a season or two. If I wanted to grow a wider selection of trough plants I needed to look for other options.

I’m not the first gardener to make a planter out of a broken birdbath – a solution that effectively creates a raised trough. My birdbath was terracotta and had shattered when an early freeze expanded the ice in the basin before I’d remembered to store it away in the garage for the winter. A wide terracotta bowl would have restored the piece to its original purpose but I decided it might be more prudent to look for a replacement that could stay outside all year. Frost resistant terracotta bowls are quite pricey so after a couple of months of shopping I settled instead on a 16-inch terracotta saucer, the kind that catches water beneath a large pot. After Randy drilled holes in the bottom of the saucer I filled the saucer with a cactus soil mix consisting mostly of crushed volcanic rock (Crump’s Greenhouse Cactus and Succulent Potting Mix) mounding the medium 2-3 inches higher in the center for greater depth.

Stuffed with various sempervivums and a couple of small sedums, I set the bowl back on the stand in a microclimate that provides full sun in the morning and shade the rest of the day. For mulch I decorated the surface with fist-sized pumice rocks and round, beige hydroponic “marbles.” The bowl is watered twice a week, which is sufficient to prevent the sempervivums drying out excessively. (In other climates it might be nearly impossible to kill sempervivums, but I’ve managed to do away with more than a few through drought and neglect.) To mitigate frost damage, I lift the saucer off the stand and sit it on an adjacent paving stone from October through April. Except when occasionally dumped over by raccoons (mothballs scattered in the mulch discourages them), this birdbath garden has been a real success.

Although somewhat porous, terracotta doesn’t appear to dry out as quickly as hypertufa, especially in this partly shaded site. On the down side, even when sold as “frost proof,” terracotta eventually shatters in winter. However the birdbath experiment did start me wondering what other container prospects might be possible—and more durable.

I’m not at all certain where the inspiration to use ceramic pots as troughs came to me from. Horticulturist Dan Johnson has been growing opuntias in large ceramic pots in the Roads Water-Smart Border at Denver Botanic Gardens for more than a decade. These are the dense, heavy, made-in-Asia glazed pots sold at every home improvement center. I’d been using a similar low and wide bowl-shaped version
for annual flowers and so already owned a few when I decided to try them with rock garden plants. The pots were not labeled frost resistant and had never been left outside over winter so trial and error was my only option. An over-sized ceramic porch pot I had filled  with perennials a couple of years before this had lasted only two seasons outside before the glaze began to slough off. A very pricy Vietnamese strawberry pot disintegrated after only one freeze. (Oddly enough, the pots that have best withstood both wide swings of temperature and sub- zero freezes are also from tropical Vietnam and Indonesia.)

After our fall member’s plant sale in late summer of 2009 I crossed my fingers and filled two 6-inch tall and 18-inch wide stoneware bowls with 1/3 peat-based potting medium, 1/3 garden loam, and 1/3 coarse sand and placed them against and below a low rock wall on the east side of my house. In went silver-leafed Tetraneuris acaulis subsp. caespitosa from Pike’s Peak, Townsendia ‘Jeane’s Purple’, and several drabas and small eriogonums. I vowed to water these no less frequently than two or three times a week. (Their location only a short distance from a faucet has been a big help.) Lo and behold, after two seasons most of the plants were not only still alive, but were actually thriving. Plus the pots were absolutely intact with no chipping, cracks or flaking. Emboldened, I looked for more of these bowls, at least 15 inches across, arbitrarily reasoning that any smaller wouldn’t hold a large enough volume of soil or provide surface space for a variety of plants. The pots are glazed stoneware (mostly of beige rather than red clay) and heavy for their size. Rapped with knuckles the sound is more like a bell than a thud.

I’ve furnished four more bowls with Western dryland tundra plants, feeling that these will tolerate my forgetful watering regimen better than alpines. Whatever their native origins, all seem to prefer partial shade. At least in Colorado, where solar radiation and ultraviolet light are much stronger than at lower elevation, morning sun and afternoon shade gives most plants enough sunlight to bloom well while providing a respite from the hottest part of the day.

Suddenly I could grow things I craved but that had heretofore refused to have anything to do with me. Dwarf alpine and dryland penstemons such as Penstemon davidsonii ‘Microphyllus’, P. paysoniorum, and P. californicus have persevered for many years in ceramic bowls, covering themselves with flowers for weeks on end. So, too, previously difficult (for me anyway) Townsendia eximia and Eriogonum kennedyi prosper in these ceramic “troughs.” Significant drought and extreme heat in 2012 followed by an arctic freeze in April 2013 and then major flooding later in the year took a toll but even so more plants survived than perished.

In the last couple of years I’ve come full circle to again try my hand at hypertufa troughs. Every year at our chapter’s spring plant sale some extraordinary works of hypertufa art show up—I’m crazy about garden art and could not long resist. The first hypertufa piece I succumbed to was a small bowl dyed celadon, its sides embellished with a line of buff rock just below the rim. Colorado artist David Jessup of Green Collar Guy Design assured me that his creation would tolerate any amount of frost but not wanting to risk it I have this pot a  tender cactus and keep it indoors over winter. At the annual NARGS meeting in Salida in 2010 there appeared another gorgeous creation by the same artist, a cone-shaped container one foot tall and as wide, of mottled green and raw ochre hypertufa molded using pieces of rough bark. Never planted because the inside of the pot is every bit as attractive as the exterior, it has stood empty on my patio without weather damage through four winters. Another local artist experimenting with nontraditional shapes for troughs was responsible for the first real trough I was brave enough to undertake. It is 15 inches square with the corners cut off on the diagonal and has been happy home to Sempervivum ciliosum subsp. borisii, Erigeron compositus ‘Red Desert’ and Draba norvegica. Since then, I’ve brought home several other hypertufa troughs of various shapes, sizes and colors.

There have always been a few imaginative rock gardeners who break with tradition to display rock garden plants in containers other than stone or hypertufa troughs. Terra cotta chimney pipes used as planters are not at all uncommon.

Resourceful gardeners make do with unlikely materials, some of the most ingenious Ottawa’s Lynda and John Soper’s troughs made from recycled Styrofoam medical-supply shipping containers. Bill Adams of Sunscapes has in his Pueblo garden a couple of large hand built ceramic containers made by potter and rock gardener Gwen Moore, while Gwen has more than a dozen such planted containers at her Lakewood home. In Holland old ceramic drainage pipes stand in for troughs. Amenable sempervivums show up in old boots, high heels, buckets, cinder blocks, logs and all manner of objects that will hold a bit of soil.

More ornamental than practical, my original two tiny troughs are similarly planted with sempervivums, the only plant that can endure in such a small space. While I still don’t have a genuine antique stone trough, my rock gardens now feature all sorts of other interesting containers—with new ones arriving every season.