The diva among houseplants - tribunedigital-chicagotribune

Yes, ferns can be fussy and temperamental to grow indoors. So why bother? Ask any diva: They're worth it.

December 02, 2010|By Beth Botts, Special to Tribune Newspapers

A maidenhair fern lives on a shelf above the shower in my brother's bathroom in San Francisco.

If you've got to be a fern indoors, that's about the best spot you're going to get: a few feet from a sunny window, swathed in a cloud of steam at least once a day in the moistest room in the house, in a climate where, even in winter, the central heating is not always on.

In Chicago, the indoor life is a lot tougher. From early October well into April, hot-air ducts and radiators dry the air like the Sahara sun.

Plants that evolved in relatively dry places, whose large, thick leaves are coated to help keep water from evaporating away, have a better shot at survival. But for a delicate, vulnerable fern native to the floor of a rainy tropical forest, living in central heating can be like being baked in an oven. My brother's thin-leaved maidenhair fern (Adiantum raddianum) would need a terrarium to make it in Chicago.

It's certainly possible to keep ferns as houseplants. In the Victorian era, a huge, bushy Boston fern had pride of place in many a parlor window. But in the Victorian era, even the well-to-do had far less efficient heating than today's average apartment.

What makes ferns so vulnerable is mainly the same quality that makes them attractive: Most species have their leaves (technically "fronds") divided into many thin, small leaflets that give these plants a light, airy presence.

All those little leaflets have lots of surface area and lots of edges — and plant leaves tend to dry from the edges in, says Deborah Moore, floriculturist at the Chicago Botanic Garden in Glencoe. She's responsible for raising many plants, including ferns, for the garden's displays.

No matter how much you water a fern — and ferns are as vulnerable to overwatering as other houseplants — it can't make up for the effect of the dry surrounding air that sucks the moisture from the fronds. To keep a fern alive indoors, "the only thing you can really do is raise the humidity in the air, and there aren't that many ways to do it," Moore says.

The bathroom is your best bet, if it has enough light. Few tropical ferns can tolerate deep shade; they don't want to be fried by full sun, but they need to be within a few feet of a window.

If you have a whole-house humidifier, use it. Or group your ferns and other delicate-leaved plants around a room humidifier. And turn the thermostat down. Cooler air holds more humidity (and you'll save on your heating bills).

It may help somewhat to elevate your fern above a little pool of water that can evaporate up around the foliage. Set the pot on some rocks or bottle caps above a saucer and keep it filled.

But don't let the bottom of the pot actually sit in the water. Like other houseplants, ferns can't live with their roots submerged. They'll drown.

Some authorities recommend double-potting: setting the fern's pot inside another pot a couple of inches larger in diameter and filling the space between filled with moist sphagnum moss. Water will evaporate up from the moss. But you will have to wet the moss often, so make sure both pots have drainage holes to allow the water to flow away from the roots.

What is not likely to help is misting the fern with water from a spray bottle. "It's going to help for such a short period of time that unless you're willing to come in every half hour and do it, it's not going to significantly affect the humidity level," Moore says.

Though they need their fronds moist, ferns like their soil evenly moist, not wet. It's always better to actually keep track of the moisture in a houseplant's soil and water when necessary than to water on a rigid schedule. Simply stick your finger into the soil; when it feels dry about an inch down, water. (If you use an electronic moisture sensor, be careful not to stick the probe down too far.)

With a couple of exceptions, ferns are "not particularly heavy feeders," Moore says. She recommends using a water-soluble houseplant fertilizer at half the strength recommended in the directions no more than twice a month, and less often in the winter.

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Boston fern (Nephrolepis exaltata): The Victorians' secret is that this bushy, classic parlor fern has fairly substantial fronds and can tolerate moderate, rather than high, humidity. That doesn't mean it doesn't need help, but it doesn't need to be in the bathroom. A Boston fern needs fertilizing more often than most, Moore says. Apply a standard houseplant fertilizer at half-strength about once a week during the summer and less often from fall through spring.

Button fern (Pellaea rotundifolia): The little round leaflets of this small fern from New Zealand are, well, cute as a button. It can tolerate moderate humidity, but it does best in brighter spots.

Cretan brake fern (Pteris cretica): Though this fern's leaflets are fairly large, it still needs high humidity. On the other hand, says floriculturist Deborah Moore, brake ferns are resilient: "They tend to some back from a little bit of abuse or unhappiness." The variety P. cretica "Albo-lineata" has an attractive silver streak down each leaflet.

Sprengeri fern (Asparagus densiflorus "Sprengeri"): Though it has the same feathery quality as many ferns, this plant is not a true fern. It's a good fallback for those daunted by ferns because it also has a soft, airy texture but is a little tougher. Still, its many small, slender leaves are quick to dry out, so high humidity is best. An attractive variation is the foxtail sprengeri (Asparagus densiflorus "Meyersii"), with its leaves arranged on dense, arching fronds. Feed either like a Boston fern.

— B.B.

Fine-tuning tips

Here are a few common ferns with suggestion for their care.