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GARDENING : Seemingly Tame Plants Can Grow Into Monsters

August 17, 1991|JULIE BAWDEN DAVIS | SPECIAL TO THE TIMES

If you've ever added a plant that looked small and unassuming to your landscape, only to watch it overtake your yard several months later, you've fallen victim to an invasive plant.

Often beautiful and alluring, certain "spreadaceous" plants charm unknowing homeowners into planting them. Such plants adapt quickly and soon grow out of control.

"The Mexican Evening Primrose has become popular recently," says Kent Gordon, horticulture department coordinator at Fullerton College. "This plant has wonderful flowers, is drought-resistant and can grow in poor soil but is very invasive. You need to plant it and stand back, because it will take over."

Though often visually appealing, certain plants such as bamboo, Asparagus fern, Algerian Ivy, Matilija Poppy, Virginia Creeper, Bracken fern and bougainvillea tend to overtake yards.

"People often choose plants in the wrong manner," says John Greenwood, a landscape architect in San Juan Capistrano. "They will pick plants for their flower color, without considering their real landscape use.

"Before you plant anything, familiarize yourself with its growth habits. Sunset Western Garden Book is a good source. It will tell you if the plant spreads easily and how big it will grow. Some plants' root structures get so large that they ruin concrete and sprinkler and drainage systems."

Not only can spreadaceous plants cause root damage, they can harm nearby plants. "Invasive plants will choke out less vigorous ones. Like weeds, they take water, nutrients and even sun from other plants," says Kathy Sommer, a horticulturist based in Corona del Mar.

Invasive plants do have some benefits, however. Often California natives, they are adapted to this climate, tend to be drought-tolerant and grow vigorously, providing the homeowner with low-maintenance landscape.

"Invasive plants can also be used as competitive plants to choke out undesirable weeds," says Gordon. "And they provide a good form of erosion control, as they bind hillsides."

Considering their benefits, you may want to add some of these plants to your landscape. "Just make sure you really like a prolific plant before you take it home, because you'll be seeing a lot of it," says Sommer.

One consideration when choosing a vigorous plant is how it reproduces itself. There are three ways that a plant can become invasive. Some spread and sprawl above and below ground, others reseed themselves and the wind blows the seed around the yard, while a third group produces above and underground runners. These are new root systems that cause the plants to spring up in other areas of a yard.

Some plants fall into more than one category, making them exceptionally risky additions.

Many vines tend to be sprawlers. They start out small but get rather large.

"It can take just a couple of years for vines to get out of control," says Greenwood. "Some vines climb by developing holdfast discs. If such a vine grows on your house, when you pull it off, the discs will stick to your stucco, causing it to come off as well. The Virginia Creeper has these discs and takes up a tremendous amount of room. Wisteria, honeysuckle and Cat's Claw vine can also get out of hand."

Though you can keep control of some vines by regular pruning, some flower less when cut back.

"The Blood-Red Trumpet Vine and bougainvillea must be left unpruned to flower well," says Gordon. "The problem is that they both take up a great deal of room. The trumpet vine has a 75 foot spread, and its trunk gets as wide as a man's arm."

Ground covers can also cause problems. Some grow uninhibited, such as drought tolerant rosemary and acacia redolens, which has small yellow flowers. The latter grows one to 2 feet high and spreads 15 feet.

Many flowers are reseeders, such as alyssum, hollyhocks, foxglove, marigolds, rose campion, Dusty Miller and cosmos. Also invasive are Fountain Grass, which has fuzzy coppery pink or purplish flower spikes and Pampas Grass, which has white or pink plumes.

Although seeder plants can be annoying when they pop up unexpectedly, they usually aren't too much of a problem if reseeding is their only means of propagating.

"Weeding these plants out when they are small is the best method of dealing with them," says Gordon. "Once a flower bed is overgrown with an invasive plant, you are faced with a lot of work and may have to sacrifice the desirable plants in the bed to remove all of the unwelcome ones."

The peskiest category of plants to control are those that spread by underground and above ground runners, which cause plants to pop up all over a yard. Though you dig up an undesirable pest in one area, you'll find it growing in another location. Many of these plants compound matters even further by also reseeding.

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