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, there is a forest of pale green ornamental kale flowering in the east window.

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

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.

She brought a few favorites with her when she left the greenhouse 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 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 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 for succulents.

Tovah Martin

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 100 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 2-foot-wide chestnut floorboards. 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). The west side of the barn, which is now the kitchen, retains its original cow-eye-level windows.

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

Martin, toughened up by years of 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.

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 houseplants, "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."

Winter light is low, too, so most plants don't need fertilizer. Though, again, the sensitivity rule applies. When the leaves of her citrus and clock vine started looking pale, she started fertilizing until they greened up again.

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.

"I don't know where I'd be without them."