Once you get past their odd name, the homemade faux-stone planters known as hypertufa containers have a place in any garden and make for a perfect spring project.
About as easy (or hard) to make as pastry, if a lot messier, they are planted with diminutive plants and have a capacity to bring a focal point and singular charm to the patio, balcony or wherever they are placed.
They are perfect for apartment dwellers just getting into gardening, downsizing baby boomers, the physically challenged (who can cultivate a whole little world at tabletop level) and just about everyone else. I have admired them for years, but only recently turned my hand to making one.
The origin of these distinctive containers is interesting. For centuries, large rectangular troughs were chiseled out of blocks of stone to provide watering vessels for horses and other livestock. When cars and trucks replaced working horses, some gardeners took the surplus troughs and turned them into mini-gardens. There aren’t many old troughs around anymore, and antique ones sell at high prices. By fashioning your own from cement and other materials, you can make them inexpensively, and they are light enough to haul around. You also get the considerable satisfaction of creating them yourself.
But be warned. “They’re like potato chips,” trough guru Lori Chips said. In other words, the first you savor won’t be the last. She is the author of “Hypertufa Containers: Creating and Planting an Alpine Trough Garden,” published in July by Timber Press.
Where does this name come from? As Chips writes, tufa is a type of porous limestone rock that creates a habitat for alpine and other rock garden plants. Hypertufa became the name for the synthetic version (did someone add caffeine?).
I signed up for a workshop at the U.S. Botanic Garden and gathered after-hours with 15 others in the conservatory’s garden court; to have the place to ourselves as the day’s light was fading was a magical experience.
The class was led by the botanic garden’s Lee Coykendall and Santos Carillo, who split us into teams of four. I’m adding Chips’s advice to the mix. Let’s get started.
Equipment and materials
You’ll want a wheelbarrow or soil mixing tub, a large trowel, old clothes, and latex gloves, plus thin plastic sheeting, such as a drop cloth. A protective dust mask wouldn’t go amiss, either. For an authentic stonelike look for the trough, you will need paint scrapers, wire brushes and even masonry tools.
The dry ingredients are portland cement, peat moss, and vermiculite or perlite. Portland cement typically sells in 94-pound bags. Don’t use concrete or quick-setting mixes. Peat moss can contain twig pieces, and Chips prefers to screen it first to produce a uniform loose powder. You will need to break up any clumps before setting the mix.
Vermiculite is a silica-like mineral that expands when wet and has been used as a soil amendment for years, though it is considered harmful if inhaled. Perlite is lava glass that has been heated to create tiny white pellets and is used as a soil lightener. The botanic garden class used vermiculite, though Chips prefers to use perlite, which she says is more stable during the setting and curing process.
Both the cement and vermiculite produce dust that you should not inhale, so handle them gently and wear a dust mask.
To give the trough added strength and durability, Chips likes to add synthetic fiber mesh — it looks like long coconut shavings, which masons add to fortify cement and prevent microcracking.
Forms give the poured mix its finished shape and can be as elaborate as a purpose-made piece of carpentry or as simple and disposable as a strong cardboard box. The form should be lined first with the thin plastic sheeting for ease of separation.
Most versions have an outer form and an inner form — the trough is made in the space between them. In her book, Chips offers a simpler version that dispenses with the inner form. The walls are built up by applying a mix by hand in courses.
In either approach, the walls should not be so thick that the proportions are off, or too thin that they are structurally weak; between one and two inches seems about right. In our workshop, we each made a small container from two plastic plant pots, the outer an eight-inch pot, the inner a six-inch one. Shallow bowls look good but don’t provide the degree of soil drainage of taller troughs.
Mixing and pouring
To make four small troughs, we added two eight-inch potfuls of each ingredient into the tub. After thoroughly blending the dry ingredients with a trowel, we made the mix into a crater, and Carillo arrived with a hose wand to put in about two gallons of water in the center. We then worked the mix gradually into the puddle until it formed a mud. Carillo judged it too dry and added a little more water (twice, after mixing each time). The final consistency was akin to soft ice cream. If the mix becomes too soupy, you have to add more of the dry ingredients — Chips keeps a mixed batch ready just in case.
We put a couple of inches of mud in the bottom of the outer pot and then inserted the smaller one. The void between them was filled. As you do this, the mud wants to sink and elevate the inner pot, so I held the pot down while my teammate, Stephen Pelszynski, fed the mix into the sides. Once we were satisfied that the space was well filled and the lip smoothed, we placed a weight on the inner pot to keep it from rising as the mix began to set.
The trough sets up by the next day but will still be soft enough to drill drainage holes — a vital feature of any trough garden. This is also the time to get the wire brush and tools to add texture to the exterior. You can install the garden within a few days of making the trough; the mix will continue to cure and harden. Chips doesn’t plant her containers until they are fully cured, which can take a month or more. She places the trough in a large, enclosed plastic bag to maintain humidity. “The longer you leave it enclosed to cure,” she writes in her book, “the stronger the trough will be.”
This is probably an important consideration for troughs that are left outside year round.
In the workshop, we were handed cured troughs made by an earlier class. Ours will be used for a future one.
Most plants suited to trough growing are deep-rooted and like it on the dry side. This isn’t a summer container for annuals, and you shouldn’t use garden or even potting soil. The growing medium recipes differ, but Carillo favors equal parts of sand, a soil amendment made from recycled glass by Growstone and a compost-based potting mix. Chips suggests a blend of a peat-based potting mix with coarse perlite and quarter-inch gravel. Another component might be chicken grit.
The plants should be small and suited to free-draining conditions. We used tender cacti and succulents. Typically, trough gardens receive alpine or rock garden perennials, bulbs, and dwarf conifers and shrubs. These are all hardy and content in troughs meant to stay outside. The tender plants – these include all the succulents that have become so popular in recent years — can spend the growing season outdoors once temperatures warm up but should come inside in a cool, bright environment away from frost by Halloween. When outside, they should be away from exposed, sunny locations.
My preference is for the hardy plants because there are more to try, even if it leads you into an esoteric repertoire. Not all high-altitude little beauties will work in hot, humid climates. Chips offers some great advice: Join the local chapter of the North American Rock Garden Society to get to know the plants suited for trough growing in your area.
The key point is this: Plant your trough with tender plants or hardy plants, but not both.
After our session, I asked Pelszynski’s wife, Jane Longan, for her verdict: “I always liked them and wanted to make them at home,” she said. She found it easier than anticipated, “but maybe that’s because they had all the materials handy.”
The fourth member of our team, an apartment dweller, Jordan Myers, said she has been coming to Botanic Garden workshops to learn about various aspects of gardening. Hypertufa was “something I knew nothing about,” she said. “I Googled it.”