If you can make room for a miniature rock garden — one of the small plants that grow within the confines of a mock rock trough — the promise of an outsized payoff awaits.
Within the walls of a trough, you can simulate the conditions required to grow chosen species that would sulk in most dug-in beds: certain colorful, sculptural succulents, as well as alpine plants from the harsh, exposed environment above the tree line.
And then there’s what Lori Chips, of Oliver Nurseries, in Fairfield, Conn., calls “the little theater” factor.
Trough gardens draw crowds, you see.
Ms. Chips tells the story of a designer and customer she has known for years who, despite his extensive experience in gardening, had never planted a trough. He bought a cylindrical one made of hypertufa – a mixture of cement and peat that simulates the look of stone – and a miniature creeping thyme to put in it. A humble beginning, that’s for sure.
On a subsequent visit to the nursery, where Mrs. Chips worked for 27 years, he talked about his low point. He had placed the barrel on his patio, where there were larger containers with more showy plants, but it was the small trough that attracted the most attention from visitors.
“Any person who came in would say, ‘What’s that?'” he reported. “Because it could be seen in a trough.”
At Oliver Nurseries, alpine plants and plants suitable for trough-like conditions are a small part of the huge range, as they have been since the nursery opened nearly 60 years ago. These tiny stars can be seen sinking into a 10-meter rock face, into the gravel bed above and, of course, in troughs and more troughs.
Selling small plants may not be the mainstay of the business, “but it’s a cow with a cachet,” Ms. Chips quipped. The nursery, in a rural setting that feels like an old garden, attracts a clientele of novice gardeners and connoisseurs who come for the carefully curated selection and the in-depth expertise of the staff.
It’s no surprise that rock garden plants are an indelible element of the Oliver DNA: Early on, nursery founder John Oliver hired Eleanor Spingarn, who is credited with starting the Connecticut chapter of the North American Rock Garden Society . Mrs. Spingarn built and planted the rock wall in the 1970s.
The showy dry-laid wall, dotted with flowering perennials and succulents with distinctive geometry, was restored and replanted this year, one of several projects tackled by the nursery’s new owners, Jed Duguid and Will Hibbs, who last years bought retail and landscaping . The two were employed by the previous owner for a long time, Mr Duguid said, and aim to carry on the traditions of the nursery.
“We try to be a planter’s nursery,” he said. “And to have some more unique things everywhere that are hard to find anywhere else.”
Including Mrs. Chips and her infectious love of alpines.
Fundamentals of the trough garden
Ms. Chips has helped keep the alpine-and-trough tradition strong at the nursery, and in 2018 her passion spawned a book, “Hypertufa Containers: Creating and Planting an Alpine Trough Garden.” It describes every aspect of the process, starting with mixing Portland cement, peat moss and fiber mesh (a polyfiber reinforcing material) to form the troughs.
Inspired by old stone sinks and yard water troughs from another era, these containers have walls thicker than those of a simple flower pot. They are also weather resistant.
But “not weatherproof,” Ms. Chips stressed.
That’s especially true if the troughs are overwintered in a very exposed spot, she added, “like on a deck, where the cold wind blows below them all winter,” increasing freeze-thaw stressors.
Even for those buying a ready-to-use container, some of the tips in the book—the same advice she gives to clients seeking help designing or maintaining containers—are essential to success.
First, it may be tempting to turn a shallow concrete birdbath into a trough, but think again. Although plants of alpine origin may look compact above ground, like tight cushions or mats, their roots need room to run.
Up in the mountains, they cling to “pockets in shifting rubble, where gravel and rock barely make up the idea of soil,” Ms Chips said. “The roots of the plants have evolved to go a meter wide and deep, where they find the coolness and drainage.”
A trough with an internal depth of at least 6 inches (15 cm) is recommended; one with 10 is better. Place a piece of window screening in the bottom to limit drainage hole blockages.
The planting medium Mrs. Chips uses starts with a peat-based commercial potting soil, such as Pro-Mix’s HP or BX formulas. If the brand of available potting soil doesn’t contain perlite, she lightens it up a bit so that perlite is as much as a quarter of the mixture. She then adds quarter inch diameter pea gravel (also about a quarter of the total volume of the potting medium she is mixing). The gravel has several advantages, resulting in less plant loss, especially in winter, because the plants remain standing better.
“Freezing and thawing is softened, because it has some rock in it,” Ms. Chips said. “I think the roots get tangled around small stones, like an anchor.”
After planting, a layer of gravel is placed on top – and not just for aesthetics. “It also helps keep the roots cool,” she said, “and weighs down the plants.”
If you’re planting a wall garden, she said, even more gravel goes into the mix — as much as three-quarters of gravel to one-quarter of purchased weed- and pathogen-free soil.
Customers with existing walls often ask nursery staff if they can be planted. Staff’s advice: Freestanding stone walls are better homes for squirrels than for plants. A non-masonry retaining wall, however, is fair game.
Planting during the construction of a wall gives the best result. But here’s a trick to try with an existing wall: Lift a few capstones (preferably the ones set a little lower than the rest) to create planting pockets for cascading plants. Line the uncovered spot with some of that soil mix. Then place the plants inside, with their roots gently teased apart and their crowns flush with the wall. Cover with a little more mix, then replace the capstone and gently water the area.
Pick the plants
The spring bloomers in that wall at Oliver Nurseries include the purple-flowered Dalmatian bellflower (Campanula portenschlagiana) and the chain-like gold flowers of Chiastophyllum oppositifolium. Like other perennials that often find their way into troughs—pink (Dianthus) and thrift (Armeria), for example—they are attention-getters.
But remember: those flowers don’t last long.
“Alpine plants will not bloom all season,” Ms. Chips said. “So you have to fall in love with each plant for its texture and habit.”
Hardiness is another consideration. Any plant that grows year-round outdoors in a container – trough or otherwise – should be at least one zone hardier than the local one, because the roots won’t have the insulation of the soil. And even if certain species are technically hardy enough, they can be extra vulnerable to winter wet. That includes most plants with silvery leaves or a fuzzy surface.
When clients seek design help, Ms. Chips offers this basic piece of advice: “I’ll say, ‘Add a hardy shrub, two other flowering plants, or a drooler or mound.'”
A “drooler”?
Yes, you heard that right: She’s talking about the smallest thyme, such as the species Elfin or madwort (Alyssum wulfenianum), and some of the groundcover sedums. They soften the edge of a trough and overflow, as if liquid falls on solid. Look for the low-growing sedums that don’t bloom early — or much.
As for the “mound,” one possibility is a rosette-shaped succulent, such as Sempervivum, Rosularia, or Jovibarba. But if you’re shopping for that, steer clear of a jar filled with a single rosette. “Don’t buy one jar with one giant artichoke in it, I tell customers — you lose everything,” she said.
Such succulents are monocarpic, meaning they die after flowering. Instead, buy a pot with different sizes of a particular succulent plant in it and encourage them to colonize in your trough by occasionally taking some babies off the mother plant and tucking them nearby.
Conifers are another element often used in troughs and other rock gardens, including gravel gardens and crevice gardens. These small trees add structure year round.
Mrs. Chips recommends varieties that are not just dwarf (slow-growing), but true miniatures (meaning they never get very tall), such as Jean’s Dilly white spruce (Picea glauca). Other favorites: a signature mugo pine (Pinus mugo Slowmound) and Chinese juniper (Juniperus chinensis Shimpaku).
Miniature irises are another possibility. They do better in troughs than in the ground, Ms. Chips said. But in her eyes, they don’t work well in a trough with a conifer unless it’s a large tank. Otherwise, the two will fight for the honor of being the upright, architectural element of the show.
“Having both will throw off the aesthetic,” she said.
The visual goal, she reminded us, “It’s about being in the land of the Lilliputians — to make your trough believable, a miniature landscape.”
Margaret Roach is the creator of the website and podcast A way to gardenand a book of the same name.
Sign up here for weekly email updates on residential real estate news.
