Pretty plants can prove perplexing to would-be intruders.
Defensive gardening--using plants as sentries--is now popular among homeowners and others concerned about security.
Using plants to limit access is quite common these days. "And not just with homeowners, but with businesses and schools," said Patrick Caughey, a principal with WYA, a San Diego landscape architecture firm that serves estates, schools, stores and businesses.
"It's often a consideration. We basically have to design burglar-proof, vandal-proof, even student-proof landscapes. We do use a lot of tough, thorny plants" to combine "aesthetics, durability and control of access."
"I've had many clients with security problems, specifically in Bel-Air," agreed landscape architect Randy Garver, whose Santa Monica-based Creative Land Design firm is frequently asked to supplement existing electronic security systems with attractive but unfriendly plants.
In one case, entertainer Lionel Richie had installed an elaborate security system that was repeatedly set off by visiting deer.
"Deer would traipse through the yard and make the system light up like a pinball machine," Garver said.
So, working in conjunction with Richie and his security people, Garver designed a landscape plan that coupled beauty with duty. Now, Richie's estate is protected by state-of-the-art electronics--and thorny bougainvillea, blackberry and raspberry vines.
Wildlife appreciates the fruit. But no four-legged--or two-legged--mammal can appreciate the accompanying thorny vines. Each berry vine grows eight to 14 feet wide and mounds as high. "I pity the person who tries to get through it," Garver said.
Years earlier, Garver planted berry vines around an old mansion he purchased with friends. The impressive old home was located in what was then a transitional neighborhood.
"The berry vines kept anyone from breaking in," he recalled. And it was far more attractive and humane than the razor barbed wire put in by the previous homeowners. Local kids liked to pick the berries."
Nature has equipped plants with many kinds of defenses. Some plants have sticky, sharp-edged or pungent leaves, while others protect themselves with thorns or irritating substances. One prime example is poison oak.
But many beautiful, tamer plants can send the same "Keep Away" message.
Garver has planted thorny roses around sections of his own home. "It's spectacular right now," he said. "Far better looking than barbed wire."
Pyracantha--appropriately nicknamed "firethorn"--is a commonly suggested plant for defensive gardening. It is favored by birds for its bright red fruit.
Carissa, including the natal plum, is another frequently utilized, generally hardy evergreen shrub. Various types feature edible fruits, aromatic flowers and sizable thorns.
Still another very popular and thorny choice is bougainvillea, a beautiful vine with soft green foliage. Its decorative bracts come in brilliant hues of red, orange, gold, purple or pink, depending on the variety selected. It is most often seen draped over fences or trellises but can be majestic cascading down hillsides.
Experts warn, however, not to overuse such plants and wind up creating a rangy-looking mess. Not only is such landscaping unattractive, but it also could require the homeowner to keep a machete in the car trunk in case the house key gets lost.
"Remember, what you're doing to prevent other people is also going to prevent you," observed landscape architect Bruce Wegner, whose career as a city parks director has made him a defensive gardening expert.
He first developed many of his ideas while working for the city of Ontario, where police asked him to help them design a program on defensive gardening for the public.
Now, as San Clemente's parks and recreation manager, he uses certain plants to separate parks from private residences and to preclude foot traffic in unwanted areas.
"From the standpoint of aesthetics, you don't want security to appear paramount," he said. "You can have both security and beauty. The real purpose is to create passive barriers and just enough of a deterrent to get people to want to go someplace else.
"Most burglars, for example, will look for the easiest access. If the house down the street looks easier to get into than yours, that's where they will head. They want all the time and hiding places they need."
Without careful planning, gardeners can inadvertently help intruders gain access. Lush trees or vines that reach a second floor are easily climbed. Too many thick plants can actually provide cover, notably along the sides of houses where first-floor windows are often located.
Wegner and others advised using carefully selected and placed plants in conjunction with other security measures, including low-voltage accent lighting, which can add drama while eliminating darkness, or even gravel, which makes a sound underfoot.
A well-planned strategy also takes into account the long-term needs of the plants, residents and dwelling. Some honey locust trees have lots of thorns, for example, but their pods make a mess and their roots can uplift a driveway.
Ask yourself these questions as you devise your security landscaping plan:
How big or messy or thick will the plant grow?
Is it against a wall that will require painting?
How will the windowsills get caulked if they are blocked by thorny natal plums?
How much pruning, feeding or watering does the plant require?
If the plant is placed next to the house, will it encourage insects and rodents or will its watering needs eventually erode the slab?
Will any ruthless, prickly plants prove objectionable to future home buyers, especially those with children?
"Within any planting arrangement, it is important to know your plants, so they don't outgrow the area or choke others out," Garver advised. "It is also important to remember that you aren't going to get access to those areas once the plants mature."
"There are plenty of plant materials from which to choose," Caughey said. "The first priority has to be layout and planning. Otherwise, the best intentions can backfire and you can do more harm than good. Design is crucial. You don't want to create the element of a fortress, especially a fortress even you can't comfortably live in."