PLANTS : Thinking Small About Big Houseplants

One trouble with houseplants is that they grow.

Eventually, plants like rubber trees, weeping figs, vining philodendrons and dracaena grow too tall for a room. And to make matters worse, as these plants press skyward, they also shed their lower leaves, leaving only bare trunks at eye level.

There is one obvious solution: get rid of the old plant and start every decade with a stocky, young plant.

But what if you have a sentimental attachment to your old plant?

A more acceptable solution might be to make a new plant from the old friend. The easiest way to do this is by a technique called “air-layering.” The advantage to this technique is that roots form along the stem while it is still attached to, and nourished by, the mother plant.

With a conventional stem cutting, there always is the danger of the top drying out before roots form. Not so with air-layering.

To air-layer, select a 6- to 10-inch segment of stem a foot or so from the tip of a branch. This is where the plant will form roots, so remove any leaves from that segment. Do not choose a portion too far from the end of the branch because older wood farther down along the stem is sometimes less inclined to form roots than is younger wood. Also, the whole purpose here is to make a short plant.

Stimulate root formation by wounding the bark. This is hardly necessary with a plant like a philodendron, which forms roots even in the air without any prompting whatsoever.

But for other plants, make the wound either by removing a half- to one-inch-wide strip of bark from around the stem, scraping the bark, or cutting a notch an inch or so long.

If you make a notch, keep it propped open with a piece of a toothpick. It helps to dust the cut surface with a rooting powder, available wherever gardening supplies are sold.

A dark, dank environment is needed to stimulate root formation. Take a handful of long-fiber sphagnum moss, wet it thoroughly, then squeeze out excess moisture as you make it into a ball.

Cut this ball in half and sandwich the wounded portion of the stem between the halves. Seal in moisture and hold the sphagnum moss in place with clear plastic film. Seal the top and the bottom of the plastic to the stem with a wrap of electrical tape. Then cover the plastic with aluminum foil to exclude light.

In time, roots will fill the ball of sphagnum moss. Every few weeks, take a peek beneath the foil, and when rooting occurs, cut the stem from the mother plant just below the root ball. If the plant is in active growth, wait until growth slows down before cutting off the air-layer.

Remove the foil, the tape and the plastic, and pot the rooted stem in regular potting soil. The new plant will need to get used to its new life independent of the mother plant, so keep it shaded for a couple of weeks while roots grow out into the potting soil.

You do still have to decide what to do with the mother plant. It is somewhat shorter since the air-layered stem was cut off, so perhaps you will want to save it.