GARDENING : Seemingly Tame Plants Can Grow Into Monsters


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.

"One plant that spreads by underground runners is Algerian Ivy, which is a broad leaf plant that can encroach in areas where it's hard to remove," says Sommer. "The Matilija Poppy is also a problem because it creates many small plants and grows over 8 feet tall. It is a beautiful native plant that has huge white flowers that look like tissue paper."

Bamboo can also cause problems. This Asian-style accent plant spreads by shallow runners and if not contained can fill a back yard with a thicket so dense you can't walk through it.

"Bamboo is not that difficult to control, though," says Gordon. "Its runners grow close to the surface, so you can contain it within any limits you want. When enclosed in a stout container above or below ground, the runners try to branch out, but hit the side of the container. For this purpose some people insert concrete sewer pipe sections into the ground that extend above the surface a little. The bamboo is then unable to shoot out runners."

Greenwood suggests using deep-root planters that are used for trees. These contain roots, causing them to grow down instead of sprawling out. If you're planting bamboo in the ground, just make sure the top of the container extends over the surface.

Ground covers that spread by runners include gazania leucolaena, which has gray green leaves and yellow flowers, and ajuga reptans, which has small spiked blue flowers. Many ferns also spread in this manner, such as Sword, Asparagus and Bracken ferns.

"The Bracken fern is one of the most difficult to get rid of," says Gordon. "It will spread from any small piece that is left in the ground after weeding. These ferns unfurl from underground. The mock Indian strawberry can also be a problem. It spreads by persistent above ground runners and seeds, as does Mexican Evening Primrose."

Many grasses also spread by seed and runners, such as Bermuda, St. Augustine and Zoysia. If your lawn contains any of these, keep the grass within borders so that it doesn't encroach on the flower beds.

"I suggest installing a mow strip along your planters," says Gordon. "It can be made out of brick, concrete or redwood and will keep the grass from sending runners into your beds."

If you have a persistent problem with a plant and weeding hasn't worked, you may want to use a more drastic measure. Herbicides such as Roundup or Cleanup will kill pesky plants and won't bother the soil. They should be used sparingly, though, as they are fatal to whatever they touch.

The secret to preventing plant riot in your yard is careful planning.

"Before planting, create definite borders for invasive plants and plan what to do if they begin taking over other areas," says Gordon. "When controlled, vigorous plants add beauty to any yard."

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