As discussed in an earlier column, many tropical species are easily propagated by "layering." Some taller houseplants that cannot be bent downwards into the soil may likewise be propagated by air-layering, which involves bringing the rooting media to the area of the subject stem where adventitious roots are desired. This procedure may seem strange to those who are not familiar with it, but have you seen Predator?

For example, my colleague Brent Green once gave me a large ugly rubber tree (Ficus elastica) that had only a few leaves on top of the otherwise bare, single trunk that was a few feet tall. It really was ugly, but what should I expect from a landscaper? I could have simply pruned the top away to promote more profuse foliar growth from adventitious buds that would emerge below. The tip of the part pruned away might have been rooted, but not as reliably as it would have been if the entire top had been air-layered.

I instead gouged out approximately a quarter of the circumference of the cambium from a section of stem approximately half an inch long. This gouge was located where I wanted roots for the upper "plant" to emerge, and approximately where I wanted adventitious growth to emerge for the lower "plant." This gouge was then rubbed with rooting hormone and wrapped with rooting media that was then contained within thick plastic wrap, which I think was previously a bagel bag.

The rooting media was actually sphagnum moss that was soaked and then drained so that it was still moist. Light potting soil is also effective, but difficult to handle and wrap. The plastic should be wrapped somewhat tightly so that the moss does not desiccate. The top and bottom may be tied or bound tightly with electrical tape. When complete, the bound media should be somewhat round and approximately as large as a softball.

If potting soil is preferred, it may alternately be contained within two "pots" of identical plastic containers, such as margarine tubs, with holes in the bottom that fit snugly around the stem. Each may be sliced on one side between the rim and bottom hole so that it can be slipped onto the stem. Once on the stem, the upper pot can be nestled into the lower pot with the slices on opposite sides, so that the lower pot supports the sliced area of the upper pot. This improvised pot can then be stabilized with electrical tape and filled. Because it is open to the air, it will require occasional watering.

When roots are visible through the plastic wrap or evident within improvised pots, the new upper "plant" may be pruned away below where it was air-layered. Remaining lower stems will then respond as if severely pruned, by producing adventitious buds. Air-layering is as practical as layering, and it may be employed to restore scrawny houseplants that only have foliage above where it is desired.

Tree of the Week: Little-leaf linden

I wouldn't have discussed a deciduous tree so late in autumn, but noticed the several mature specimens of little-leaf linden, Tilia cordata, on Clark Way in Willow Glen were still foliated and dark green. These are some of the largest I have seen, exceeding 40 feet tall and 20 feet wide. They must be old because lindens don't grow rapidly.

Small, pale white flowers that bloom in midsummer are not remarkable, but are somewhat fragrant. Leaves are typically less than 3 inches long and wide. Contemporary cultivars offer more variety than was available when the trees were planted on Clark Way, but are still somewhat rare. Aphid has unfortunately been a problem among lindens during recent years, causing annoying exudation of honeydew and damaging many trees.

Horticulturist Tony Tomeo can be contacted at 408-358-2574 or at LGHORTICULTURE@aol.com.