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IN THE GARDEN

Gardening : Enjoy In-Between Shrubs, Then Replace Them

March 15, 1992|ROBERT SMAUS | TIMES GARDEN EDITOR

A lot of very nice plants being used in new gardens are short-lived, something people find perplexing.

Some are called "subshrubs" in botanical texts, a quizzical classification if there ever was one, or "shrubby perennials," even though they do not die down for the winter. A few are labeled "shrubs" even though they are quite small and others are simply called "herbs," a real catchall.

The point is, they are not your typical, long-lived, cast-iron shrub--a rhapiolepsis for instance--nor are they soft perennials that nearly disappear every winter--like a coreopsis. They are something in between, sort of like semi-permanent ink.

The various Artemisias, Lavendulas (lavenders) and Senecios are good examples. These are all hot, new plants grown for their stunning silvery gray foliage, which brings sparkle and light to drab, all-green gardens. They also happen to be drought-tolerant, which hasn't hurt their popularity.

All stay relatively low and dense, at least at first, though they may spread quite wide.

But, after a few years, the center falls apart and the plant flops open like a dropped bag of cement. They begin to get twiggy and, a few years later, they will probably die or look so shabby that they must be removed. This is their nature, and there is nothing wrong with it.

Some people see this collapse as a sign that the plants need water, but the plants seldom do because they are all Mediterranean types quite used to doing without much water. Try to perk them up with watering and they die of root rots. In short, you're not doing anything wrong, these are just short-lived plants.

Los Angeles landscape designer Chris Rosmini uses all of these in-between plants in her designs. Every few years when they begin to look a little peaked she simply replaces them with fresh plants. "Why should plants be permanent?" she asks.

Rosmini uses them because there is nothing else quite as good or as fast to fill in. All these plants are quick growers.

A tiny lavender plant can grow to three feet across in a year, a senecio can cover four feet and some artemisias will sprint to six feet around in a season. But, as is often the case with plants, speedy growth makes for a short life.

Why not simply cut them back after this fall from grace and let them start over? These not-quite-shrubs resent it. They do not recover when cut hard, back into what gardeners call "old wood."

"They're very much like a marguerite," said Rosmini, of another plant that grows quickly, then falls apart and finally dies or collapses. But that doesn't stop people from growing daisies.

Robert M. Fletcher, a landscape architect on the Westside of Los Angeles, has a temporary solution that he's been experimenting with for several years. He lightly trims these plants frequently, sometimes three times a year. This keeps them dense and they last longer in the garden, though still not forever.

"It's hard for people to do because sometimes this means cutting off the flowers along with the foliage," he said. "It's really hard to shear a lavender in full bloom, and they're almost always in full bloom."

He does it in the late fall so the flowers are back for winter and early spring. They quickly rebound. If the plant again looks leggy after flowering, he trims in late spring, and sometimes again in summer. He even follows this routine with rosemary, which is much more durable and shrublike than the others, but also has a tendency to fall apart and get scraggly.

The idea is to keep on top of the trimming so plants don't get top heavy and collapse. Trimming means cutting off only a few inches, nothing drastic. You can even do it with hedge shears. Just go lightly and stay out of that old wood. If you observe this behavior in other plants you can try these techniques on them too.

However, even this regimen will only postpone the inevitable. Eventually the plants need replacing, "about every five years," Fletcher said of the artemisias, lavenders and senecios, but not the long-lived rosemary.

Favorite artemisias are A. arborescens , which has large lacy leaves and grows to six feet around, and the cultivar 'Powis Castle' which is smaller in all its parts and only grows to about three feet wide.

S. vira-vira , also sold as S. leucostachys is the senecio most liked by designers. It makes a fluffy, silver, two-foot tall by three-foot wide mound. Other senecios are usually sold as dusty miller and are more common at nurseries.

There are many lavenders but the favorite right now is the new Lavendula pinnata buchii , more commonly sold as L. multifida or L. canariensis (it is from the Canary Islands), with it's bright, branched flower spikes.

A good time to plant any of these is right now, well before the heat of summer arrives. By that time they will have grown a lot and will be sparkling in the summer sun. But, be forewarned, they are not forever.

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