ROXBURY, Conn. — Tovah Martin can’t live without plants, so in the winter she makes her garden indoors. Even when it falls to zero outside, as it did last week, there is a forest of pale green ornamental kale flowering in the east window.

And the fern in her bedroom window upstairs has vigorous green fronds, loaded with spores. Meet Polypodium formosanum, the grub fern.

“Look at its caterpillar feet,” she said, parting the fronds to reveal the fat blue-green rhizomes at the base of the fern. “That’s how it creeps along the ground.”

Martin, 59, has devoted her life to houseplants — not to mention the hundreds of hardy ones outside, now in deep freeze on this little seven-acre remnant of a dairy farm. The author of a dozen books, including “The New Terrarium,” published in 2009, and her most recent, “The Unexpected Houseplant,” out last year, Martin spent 25 years tending the citrus, herbs, scented geraniums, begonias and a mind-boggling jungle of other tender plants crammed into Logee’s Greenhouses, in Danielson, Conn. The renowned growers hark back to 1900, when William G. Logee fell in love with a Ponderosa lemon tree that still grows in one of the glass houses. (Plant people go in and out of this place like squirrels in an oak woods; if you can’t find it at Logee’s, why bother to grow it?)

She brought a few favorites with her when she left in 1995, but the rest of her plants soon found their way here, like strays to a good home. Once, Martin tried to count how many plants were growing in her house. “I gave up at 200,” she said.

Most of them go out in the summer and come back in before frost. Others, like Asplenium nidus, a bird’s nest fern that thrives with a plain old philodendron (one of those plants nobody can kill) inside a terrarium made from a giant apothecary jar, are permanent indoor residents.

What strikes the eye right away is that these are not just single potted plants. Each one is flourishing inside something interesting: here, an industrial metal container; there, an ancient-looking clay pot with an unusual shape or patina; maybe some old trunk serving as an indoor window box; and even a kitchen colander (great drainage!) for succulents.

They are grouped, with an eye for complementary shapes and textures, leaf patterns and colors, as well as their need for light. That flowering kale, for instance, whose trunks have taken on the look of palm trees, is illuminated to near transparency in that east window.

“White Peacock is the variety,” she said. “I didn’t want to let it go, so I potted it up and brought it inside. Then I watched it flower, and now I’m addicted to it.”

These kale plants march in a line, in a weathered wooden window box. They share the window with a jasmine, its tendrils curving toward the light, higher up, thanks to its position on a tall Arts and Crafts plant stand in the corner of the living room.

The room looked too dark for a jasmine to bloom. (West, not east, is the best exposure for houseplants in winter.) But this jasmine was a vigorous dark green and full of buds.

“It’s got a lot of windup time,” Martin said. “It probably will bloom in March.”

So how come my jasmine plants never bloom, before they shrivel up and die, inside the house?

The trick, she says, is to leave the plants outside through the fall, as long as possible. They will form their buds in the cool weather; bring them inside just before frost.

Granted, Martin and her plants have an advantage. They live in a converted barn connected to a 1790s cobbler shop by a glass corridor — the greenhouse, where a hundred or so potted plants bask in the full light, on a three-tiered bench painted sky blue.

The little 18th-century dairy barn was thankfully not mangled by its former owners, who turned the east side into a great room that has 30-foot ceilings and its original two-foot-wide chestnut floor boards. They also opened up the east wall with large paned windows that now look out over Martin’s extensive summer gardens (which include a shed and pasture for her goats, Flora and Beatty). But the west side of the barn, which is now the kitchen, retains its original cow-eye-level windows.

They are just the right height for Martin. “I’m the only one who doesn’t have to lean over to look out,” she said. “I’m under five feet.” (Exactly how tall she is, she won’t say.)

But the most remarkable thing about this house is the bone-chilling temperature.

Martin, toughened up by years spent living in a drafty Victorian house on the grounds of Logee’s Greenhouses, keeps the thermostat at about 55 degrees. Daytime temperatures rise above that, of course, in the sunny glass corridor, but it’s definitely cool in the other rooms, especially at night. “I’ve gotten used to it,” she said. “My sinuses won’t take anything else.”

Colder than that, and the subtropical citrus plants would drop their fragrant blossoms. One vigorous Calamondin orange was loaded with fruit the size of golf balls.

But for most house plants, “temperature isn’t that critical,” Martin said. “Moisture is the issue.”

So even if you and your plants live with clanking radiators that can’t be turned off — or worse, forced hot air — high heat isn’t the killer. It’s dry air.

“If you add a humidifier, that will be good for you and the plants,” she said. “They run out of moisture, and so do you.”

Divorced in 1996, Martin lives with Einstein, her Maine coon cat, who never crackles with static electricity when she pets him. As she put it, “If your cat sparks when you pet him, it’s too dry.”

As for how often to water the plants, that depends on the needs of the plant. Begonias and geraniums, for example, like to dry out before a good soaking. Ferns love moisture. And succulents can be killed by too much water.

“I don’t say water once a week or once every three days; I go by the sensitivity rule,” Martin said. “Water when it’s dry.” (And dry is relative to the plant, so don’t let leaves wilt, or soil get as dry as cement.)

Winter light is low, too, so most plants don’t need fertilizer.

“I use fish emulsion for everything, but I stop at Thanksgiving,” Martin said.

Though, again, the sensitivity rule applies. When the leaves of her citrus and clock vine started looking pale, she started fertilizing — a half-strength solution of fish emulsion, every few days — until they greened up again.

She uses organic potting soil for most plants, adding charcoal to the mix for terrariums and grit for succulents. A reputable local source for compost is best (she uses one from McEnroe Organic Farm, in Millerton, N.Y.), because it’s more apt to be full of nutrients and microbes than a commercial blend sitting too long on the shelf.

“The Unexpected Houseplant” is full of such tips. And speaking of unexpected, Martin urges adopting almost anything (barring a large tree) as a houseplant. “I always bring a conifer in,” she said, touching the dark green filigreed needles of a little chamaecyparis in a handsome industrial pot. “It makes me feel like it’s a garden indoors.”

The trick to keeping an evergreen happy is to give it a deep container.

“Or else they dry out,” she said. “The root ball is too massive.”

But it was the bathroom that swept me away. Here, among the orchids and bromeliads, the begonias and peperomias, the aloes perched in an old red colander with blue glass electric insulators, Martin can take a bubble bath in her jungle.

“I don’t know where I’d be without them, they’re so therapeutic,” she said. “It’s like this huge family.”