In a terrarium, it’s always gardening season
During the months when you can’t be outside working in the garden, what could be better than a miniature landscape that sits in your living room?
Just remember, as you put the finishing touches on your first terrarium and celebrate by cueing the chorus of “It’s a Small World (After All)”: This is a tiny garden, not a scaleddown theme-park installation where the scene is picture-perfect day after day.
“It’s not a diorama, and these are not plastic plants,” said Patricia Buzo, a terrarium designer who owns Doodle Bird Terrariums in the suburbs of St. Paul, Minnesota. Buzo’s terrariums are living gardens that she plants with narrow tongs and then prunes with shears more appropriately sized for manicures than hedge trimming.
The same rules that apply to tending your garden outside also apply here: Choose the right plants, and put them in the right place. Or else.
Your subjects should be selected not just for their good looks but for their compatibility with the environment you’ll prepare for them — inside a container of a particular size and shape — and with one another.
Shallow containers may make good homes for open-dish gardens that are more forgiving, like a bowl of succulents on a sunny windowsill. But in a conventional terrarium — a vessel that has a lid and is closed at least some of the time, or has a narrow opening — the conditions are different.
For one thing, the environment is more humid. It was that heightened humidity that allowed the Victorians to cultivate orchids and ferns at home in otherwise inhospitable environments, conjuring diminutive versions of the dreamy splendor inside the grand climate-controlled conservatories of the era.
Buzo, a former mural painter, began her terrarium business in 2008. “I work tiny now and in 3D,” she said.
When she sees a closed jar planted with cactus on Instagram, or succulents combined with moss, she can predict the outcome: “Even if it looks nice now, it isn’t going to last.”
Buzo, author of “A Family Guide to Terrariums for Kids,” offered this advice: “If you’re mixing plants, pick ones with similar needs.”
Maria Colletti, owner of the Westchester, New Yorkbased Green Terrariums and author of “Terrariums: Gardens Under Glass,” agreed. “Let’s not just plop some plants in a jar,” she said. “I wouldn’t put palms in a forest scene.”
Apart from the visual incongruity, there’s a bigger problem: Tropical plants and temperate woodland types won’t cohabit happily, said Colletti, who began making terrariums around 2006, when she was shop manager at the New York Botanical Garden, and now teaches how-to workshops.
Whether the desire to grow certain plants or to show off a spectacular container comes first, the two must be aligned.
Again: What works within the humid environment under a bell jar or inside a narrow-mouthed lab flask is quite different from what flourishes in an open bowl or an uncovered fish tank.
Another consideration: What is the available light where you will display the terrarium?
Bright, indirect light is generally most suitable, because many terrarium plants come from tropical understory habitats. But even terrarium plants that prefer direct light — certain carnivorous species, for instance — would cook inside a closed or narrowmouthed vessel on a sunny windowsill. Using an LED grow light that emits little heat would be a smarter choice.
Preparing a terrarium is not like filling a traditional flowerpot. It is part terrain-shaping and part creating a rooting zone
— all supported by a base layer of pebbles, as a terrarium has no drainage hole. Pebbles create a reservoir for excess moisture, so the roots don’t rot.
Next comes the planting medium, chosen to suit what is being grown. Most tropical plants do fine in a peat-based houseplant potting soil. Some terrarium designers spread activated charcoal between the drainage and soil layers; others mix a little into their potting soil, which should be packed down once it’s added, and then repacked, where needed, after the plants are put in place.
Another difference between terrariums and potted plants, Colletti reminds her students: In glass terrariums, all the “underground” layers will be visible.
Colletti sometimes uses colored aquarium sand in the drainage layer to complement a design. But whatever media she layers into her creations, she places construction paper cut to fit the container’s shape between applications of stone, sand and soil, to keep them from seeping into one another.
“You don’t see it,” she said. “But it’s a subtle thing that makes a difference in the final product. It’s all about the small details — the small steps — with a terrarium.”
Many terrarium landscapes become dreamier with the inclusion of moss, which loves a humid, closed environment.
Or moss can be the whole story. It is forgiving in low-light conditions and has no roots to rot. Another plus is its cold-hardiness, meaning mail-order sellers may ship it later in the year than other plants. (A homemade moss terrarium as a gift or a holiday centerpiece, perhaps?)
In her moss creations, Buzo uses coconut coir as the planting medium over the usual base of drainage pebbles.
Good candidates include pincushion moss (Leucobryum), which grows in pillowlike tufts “like tiny, grassy hills,” Buzo said. Rock cap moss (Dicranum) is a little taller; at the back of terrariums it simulates miniature pine trees. Sheet mosses like fern and feather moss (Hypnum and Ptilium) grow in dense mats, resembling so many little ferns.
And while we’re on the subject of ferns: Although they might seem like obvious terrarium subjects, many get too tall for terrarium containers. Besides the fern moss, another appropriately sized lookalike that Buzo uses is a fern ally called spike moss (Selaginella), which despite its common name is not a moss.
How often do you need to water a terrarium? That depends on the evaporation rate, which is influenced by the terrarium’s size, whether it is closed or open, and by various environmental factors.
Closed units can go months or longer without watering. More water may be required in open containers during indoor heating season or in arid climate zones. And some terrariums that do fine when they’re open during humid months may do better partially or completely closed in drier months.
The water you use is at least as important as how often you apply it, because the chemical additives and high mineral content in tap water can build up, causing havoc in small, closed environments. Buzo recommends using distilled water; spring water or collected rainwater are backup possibilities.