MOST TROUGHS INCLUDE stone as an element of the miniature landscape. Sometimes it is a single stone that will inspire a whole design. Stone can be the most dramatic feature or an impeccable supporting player. Knowing what stone to look for and why simplifies the process. Here are some thoughts to help in the quest.
Rocks and the Gardener
Every rock gardener I have ever met has a complicated relationship with stone. The majority have at the very least a well-developed appreciation for its inherent beauty and most, from experience, have a healthy respect for the sheer strength it takes to move a piece of it. I always sense a fundamental challenge there, buried deep in the rock daring me to make use of it. The bigger the rock is, the bigger the challenge. There are good reasons why rocks are usually an integral part of a trough design. The roots of alpines love to live in the company of stone. Be it a deep rock outcrop, fist-sized chunks or smaller gravel, the plants tend to thrive. The rocks offer a cool root-run, a place where rain will channel down. Stone slows temperature changes and helps prevent frost heaving. But I think it is in the aesthetic realm that a beautiful piece of stone makes its strongest case. Nothing partners with small plants in a container quite so dramatically and so well.
It has been quite sanely argued that it is possible to grow outstanding alpines without stone of any kind. A quick and envious glance at the show benches in the U.K. loaded down with potted beauties will confirm this. But the use of stone is an aesthetic choice besides a cultural one. We in New England have come to terms with the rocks we cannot get rid of anyway. New England’s tilth is the soil that grows rocks. That’s why since colonial times we have been forever building stone walls. Not always was it a need for a wall, I think, what we wanted was clear land. There are plenty of other locales with their signature rocks; I have swooned at the red-orange rocks of Utah spangled with various colored lichen. My table and mantle are adorned with gorgeous chunks of petrified wood, mesa-like specimens from Colorado and the Dakotas, prized pieces from the Cascade Range in the Pacific Northwest, many carried down a mountain in the backpack of my resigned but accommodating husband, who often, by the time we reached the base, was dragging his pack behind him.
A Personal Relationship with Stone
Even before alpines and troughs pulled me into orbit, the practice of meditating on the beauty of any given stone was not new to me. I come from a family entranced by stone. At our family homestead, my father and grandfather built two monolithic walls from stone collected from our property. These walls formed the imposing front of our Frank Lloyd Wright-styled house. They also built an enormous two-storied fireplace, the bottom level hearth aproned out with irregular field stones that were met perfectly by a templated wood floor looking like a tide line at the beach. My Lithuanian grandfather started his days by tramping the land and pulling stone for my artist father to approve. Although he did not share Dad’s taste for craggy, lichened, weathered rock, he gathered it. I remember conferences between the two of them before my father had to make the train for his job on Madison Avenue. They talked sizes, width, shapes, for the ideal stones for that week’s level in the wall. These pieces were almost never broken or chiseled. It was some kind of commandment; stone should come from nature, not be tampered with. Sometimes the wall grew incredibly slowly one row at a time. At others, it might leap several feet upwards. Once, painfully, several feet had to be deconstructed. The culprit was a stone smack in the center, too pale, too regular in shape, too squared off. It stood out like a sore thumb and troubled my father for days. It had to go. Given the sheer labor it entailed, this was an incredibly difficult decision to make. They were working on a scaffold with ramps and pure old-fashioned elbow grease. I remember that as the kind of week to avoid at all costs, but out the rock came, and the rebuilding began. We as a family celebrated the completion of those walls. They were very beautiful. I took a double exposure photograph of my father against it.
Different Kinds of Stone
Lucky for me the pieces of stone I wrangle are generally a lot smaller. They have to be to grace the inside of the troughs I work with. I have a couple of prejudices I freely admit to and share with anyone coming to me for ideas. Do not haphazardly collect chunks of your favorite minerals and try to gang them together in one schizophrenic landscape. A piece of pink quartz, a lump of tufa, a few slivers of slate, a craggy hunk of granite and some polished beach stones will argue together, aesthetically speaking, till the end of time. Confine yourself to one sort of rock in one container at a time. And always try to find gravel mulch that mimics the stone you use for harmony and believability. This does not mean that once you finish one trough with certain elements you are constrained to abide by that from then on. Part of the beauty of trough gardening is that we can be inspired anew each time we approach a new container. If the first trough has gray weathered material, you can decide to use dark obsidian tones next time. A trough featuring terra cotta-colored stone and planted solely with silver plants is a revelation.
Look for angular rocks. They are infinitely more inspiring to design with. A collection of them can mimic a natural outcrop, a bluff, a mesa, or a gorge. Baby plants can be sandwiched between the flat sides of angular pieces; their roots will love the cool environment of the buried stone, and the plants will thrive. Whenever I travel or even hike locally, I always have a little part of my mind tuned in for the next handsome stone I might find, the one that will form a gorgeous backbone in a container, that will become a ledge or focal point, the more architectural the better.
There is one big proviso I would be remiss not to mention. One cannot collect stones with impunity just anywhere. In state and national parks, it is strictly forbidden. If you happen to be on someone else’s land, you must obtain permission. Some rocks are even the equivalent of “endangered.” The stones in the Petrified Forest National Park in Arizona qualify. I suffered agonies of acquisitiveness during my visit there. The Park officials grill you on the way out in case you pocketed a gem or two. I knew better. But we pulled into the next rock shop we passed after leaving. Then too, not all rocks are hardy. Some beautiful sedimentary orange ones we brought home from the southwest picturesquely crumbled to gravel in our wet and frozen climate. It was charming to watch this process but soon, in a season or two, even the gravel was gone.
No matter if you call it gravel or grit, as long as it’s made of stone, adding a mulch of it to the surface of your trough is unquestionably a good idea. Aesthetically it completes the project, makes it look polished, but it goes beyond that. These little mountain plants come from a habitat of stony soil. As with any mulch, gravel will protect the soil from drying out. I can’t claim that it will “Hold down weeds,” a phrase often proffered about bark mulches. Seeds love to germinate in gravel. But on the positive side, things seeded into gravel are very easy to pull out. The stony surface will also keep the soil cooler, hugely important to alpine plants. Stone mulch tucked carefully under the cushions keeps the foliage from being in direct contact with the soil. The crown of the plant, the point at which the root and shoot join, is usually the most vulnerable part of an alpine. A collar of gravel is added insurance.
There are many gravel sizes out there. This is a choice, but if you use one much bigger than ¼ inch (6 mm) it may begin to ruin the scale of the design. Conversely, extremely fine particles like sand can hold wetness, just what you want to avoid. Avoid Turface® as a mulch. It can be a good additive to a soil mix if done with a light hand, but at the crown of the plants it will hold water just where you don’t want it. For some of the more difficult cushions you might try mulching by placing flat thin flakes of stone under the skirts of the dome, up to but not touching the stem. This can help cushion plants to sail through the harder times of the year when humidity or rain or slush can hurt them. It is not a trick that can cure every climate woe, but it is another tool to wield.
Remember that rock is either acid, neutral, or alkaline, so choose accordingly for the plants you have selected. Generally, neutral is a safe bet. Some examples of subjects that prefer an alkaline reaction are dianthus and gypsophila. Acid lovers are members of the ericaceae. A few examples are Calluna, Cassiope, and Rhododendron species, as well as many conifers.
On a purely aesthetic level, think about the color of your mulch. The gravel mulch is the canvas, the common denominator, even the referee of your plants. Alpine species tend to have fairly clean unmuddied colors. But even so, flamingo pink and egg yolk yellow are hard to marry comfortably. The gravel you choose can help; it performs as a mediator between the plants. Think of what plain green or that swath of silver-gray does to mellow a color combination in a flower border. Choose gravel that plays well with the rocks you plan to use as elements in your little landscape and choose gravel with various tones mixed in, such as browns, tans, and several grays. Gravel of all one color looks flat and is reminiscent of the traprock used in roadways. It should look natural, like random pebbles you see on a path. Right here I will make a value judgment. Never use blinding white quartz no matter what you plan to combine it with, or where you live. Except, maybe, Crete. In which case, I am sure I can free up some time to come over to help….
How Much Stone to Use
Students are often startled by the quantity of stone I will sometimes puzzle-piece together in a single container. I do realize that this makes for a heavier trough. I just plan to move it around less. There is something epic that begins to happen to a container once a massif is formed. Even the way the plants are added, and how they read undergoes an aesthetic shift, an interesting one, one truer to nature as we find it in the mountains. When working in this way the stones become the focal point of the trough.
You may have a soft spot for alluring beach stones. So do I. I cannot count how many pounds of these I have emptied out of sandy pockets in my lifetime. I love their shapes and colors, the smoothness they have after tumbling endlessly in the surf. Sadly, they are not the easiest to use in a trough garden. One does not find a lot of round rocks on mountaintops.
You could try a Zen design might with beach stones; I can imagine a lone wind-tortured shrub, some mosses and an array of carefully graduated stones either by color or size or both. But this is a different discipline closer to bonsai. Attempting to design an alpine landscape with round polished stones has proved problematic, especially since alpine cushions and their flowers look so perfectly at home when tucked up against a craggy rock. So, in general, opt for the angular every time and put your beloved beach stones in a beautiful bowl inside (or outside) the house.
When placing these more structured stones examine each one. Most irregular rock has some stratification, in placing several together be consistent with these angles. To create a believable outcrop, you must obey this geologic reality, uptilt them with the strata all going in the same direction. There seem to be people with an aptitude for breaking these particular rules and having it work anyway. It seems to be a talent one is born with. But if you, like me, are not one of these lucky ones grant yourself a more assured success. Study your stones before placing them and obey their lines.
The Perfect Stone
As I write this at my dining room table, I am surrounded by rocks. I thought they would be good inspiration. There are a couple on the chair next to me, a nice collection on the table, the windowsill holds more. Not every one of them is beautiful, but all captured me enough to bring them inside for second looks. As I collected them to bring in, I realized that I am always looking for the perfect stone. Some cultures believe that spirits reside in stone. As I cradle one in my hand, I find that is not hard to understand.
In the final analysis did I find the perfect stone? Yes. And no. There are stones perfect for their spot in the garden or trough, soulful chunks in the landscape that I regularly visit, even perfect stepping stones. The perfect stone is the one I have in my hand right now. But it is not that simple. It is also the very next stone I covet whether I see it in a stone yard, at the edge of the path underfoot or the one I slip into a backpack to lug down several thousand feet. One of those lives on the mantle, cheek by jowl with another cherished one from the family homestead not that far away from where I live now. To make the matter even more complex, there are gorgeous stones in landscapes, even in walls and jetties no one would think of disturbing or moving. Therefore the motive of possessiveness is not it either.
The perfect stone, it turns out, is only perfect if it fulfills the reason you want it. A hearthstone or lintel are different creatures compared to the stone inside a terrarium. A mason’s perfect stone and that of a mineral collector or a bonsai artist will all differ mightily. Stones are strong, nearly permanent, and beautiful. What they offer sometimes needs to be unlocked by working with them. And we are by no means the only animals drawn to them. The perfect stone for our very discriminating cat is the smooth, comfortable one on our driveway bench, with a concave spot that is perfectly sun-warmed, cradling her perfect face. Queenie is a cat who knows a lot about perfection. And I wouldn’t dream of arguing with her.