Tough Trees : Finding Hardy Plants to Weather the Drought

By summer a lush lawn may be a luxury of the past, but who can imagine a landscape without trees?

In dry times even ordinarily hardy trees, especially those accustomed to regular irrigation, can succumb. Once weakened by drought, they become susceptible to pests, disease and pollution.

Watering of trees is one of the few outdoor uses of water that will be allowed under the water conservation plan adopted a week ago by the San Diego County Water Authority.

The regulations, which go into effect April 1, permit trees and shrubs to be watered using a bucket, drip irrigation, or a hand-held hose that includes a shut-off nozzle. Sprinklers may be used to irrigate trees and shrubs planted in turf and ground cover, but only once every two weeks.

Although most native and non-native trees and shrubs suitable to our environment should be salvageable, some thirstier species may go the way of turf. And, by the time rain returns in earnest, Southern Californians may have learned to rely more strongly on plants naturally suited to this climate.

Actually, the Southern California landscape, including North County, does not offer a naturally tree-rich milieu, says R. Mitchel Beauchamp, author of “A Flora of San Diego County, California.”

This is especially true if certain types of trees are excluded: those found above 3,000 feet (like the big cone Douglas fir on Palomar Mountain) and along streams (like the willow and California sycamore along the San Luis Rey and Santa Margarita rivers). These trees do well in the specific environment where they are already established, but do not thrive in the Mediterranean scrub flora communities most common in North County.

Although everyone has his or her own favorites, a few trees and shrubs emerge as definite winners for a variety of landscaping situations from Del Mar to Oceanside, Carlsbad to Escondido.

In this climate, just determining what is a tree can be tricky. A number of plants that are technically shrubs grow to the size of trees.

Trees are defined in P. Victor Peterson’s book “Native Trees of Southern California” as woody plants “at least 10 feet high with a distinct stem or trunk not less than 2 inches in diameter and, except for unbranched yuccas or palms, with a more or less well-defined crown.”

About the oak, there is no doubt.

“What is more characteristic of the California landscape than the oak,” writes Sharon Johnson in “Living Among the Oaks,” a publication of the University of California Cooperative Extension. “Round-crowned oaks dapple the rolling hills, solitary monarchs shade our rural roads, and valley giants stretch skyward in banners of leaves and lichen. Past and present-day travelers have stopped in awe of our native oaks, and countless photographs and memories are framed by their spreading, weather-worn branches.”

California Indians prized the oak beyond its appearance, and some researchers estimate that more than 50% of their diet consisted of acorns, which were ground and used for mush or cakes. Oak trees offer shelter as well as food to birds and small mammals.

The coast live oak, an evergreen tree with low spreading branches, and the Engelmann oak, which is often mistaken for the former, are particularly suitable for North County. Because of its smaller size, the Engelmann oak makes more sense in the average garden.

Also known as the mesa oak, the Engelmann grows naturally in a limited area, primarily in western San Diego County.

Dedicated to preserving the Engelmann, a small group of admirers led by the late Frances Ryan planted trees grown from acorns in Escondido. Of particular note are the trees at the Ryan Oak Reserve, including one that is nationally registered, and at Oak Glen Elementary School.

Biologist Brad Burkhart, revegetation manager for ERC Environmental and Energy Services Co., developed a class on native plants that he now teaches at Quail Botanical Gardens. Of the 20 species of Pinus native to California, he singles out several: the torrey, Coulter, digger and Bishop pines.

Although the Torrey pine has suffered losses because of the drought at the Torrey Pines State Reserve, home gardeners do not have to hold back a little supplemental irrigation as the rangers at the park are required to do.

A sprawling tree when exposed to offshore winds, Pinus torreyana may reach a height of 50 or 60 feet if planted away from the ocean.

“The Coulter pine is used to a little bit higher elevation but can do well in lower elevations, and the Bishop is potentially useful near the coast,” says Burkhart.

Sometimes described as a tree you can see right through because of its sparse long needles, the digger pine was scorned by the early settlers, especially since it had little value as lumber. The Indians, however, relied on the tree for its seeds and cones. The settlers often lumped all California tribes together, calling them Digger Indians, and may have given the Pinus sabiniana that name with equal contempt.

Other appropriate trees mentioned frequently by local botanists and landscape architects include the Mexican elderberry, Catalina ironwood, Mexican paloverde and Tecate cypress. Tall shrubs that receive equal praise are the lemonade berry, Catalina cherry, tree mallow and toyon, among others.

The toyon, also known as Christmas berry, occurs naturally on semi-dry slopes in Camp Pendleton and Palomar, and has become increasingly popular in home gardens. The tall shrub with its toothed foliage, cream-white flowers and red berries, has also been extensively used in native plant gardens at public facilities such as the Carlsbad Public Safety and Services Center and the Carlsbad Municipal Water District.

Unfortunately, some experiments with native plants and trees have not lived up to their promise, partly because, as landscape architect Kay Stewart puts it, “many people think low maintenance means no maintenance.”

“What it really amounts to though is that there is no free lunch,” says Stewart. “You don’t need to mow everyday with native plants, but you do need to do extensive weeding approximately once a month.”

Also, since native plants take a season or two to become established, the look of low-water gardens may not appeal to people at first. In public projects, says Beauchamp, it is probably best to have a ribbon-cutting ceremony three years after the plants are put in the ground.

But, as the reality of life in a semi-arid environment with an overwhelming dependence on imported water sinks in, so does the need to plant appropriately. Rolling lawns, tropical trees and thirsty flowers just do not fit.

Burkhart emphasizes that very little objective research has been done on drought tolerance--the ability to survive long periods with little water. Despite the absence of scientific literature, certain native trees make more sense in this arid climate than those that occur naturally in climates with heavy rainfall.

Interest in native plants waxes and wanes periodically, according to James Dice, president of the San Diego chapter of the California Native Plant Society.

“Ten or 12 years ago there was a lot of interest in native plants, and a handful of nurseries sprang up,” says Dice. “Now there is only one, Weber’s, which is going out of business and will leave a huge void.”

Weber Nursery in Encinitas will stay open until its stock is sold, probably within two or three months, says manager Jeanine De Hart. The business is no longer compatible with the residential area in which it is situated.

Although other nurseries carry some natives, none specialize in the area. Home gardeners committed to planting natives sometimes have difficulty obtaining plants or seeds.

The next closest supplier of native plants is Tree of Life in San Juan Capistrano. The nursery is open to the public on Fridays only and carries more than 250 varieties of natives.

For those whose gardens already sport natives, the prognosis is encouraging. According to Jeff Bohn, co-owner of Tree of Life, established trees and tall shrubs will not need any extra help beyond mulching to survive the summer.

“For plants which are not established yet and any others which appear stressed, water slowly and deeply,” Beauchamp recommends. “If it’s legal, put out a hose at night so it barely dribbles and forms a deep wet pattern. Or dig a small hole, 2 or 3 inches in diameter, and pour water into the hole.”

The trick for trees lies in deep watering, which draws roots down. Trees planted in lawns or which otherwise receive shallow irrigation are vulnerable to dehydration and may even blow over in strong winds.

Natives will not be the only survivors though, since certain imports, especially those from climates similar to ours, should also weather this dry spell. Some imported trees such as the eucalyptus have become so ubiquitous that we assume they’ve always grown here.

The genus Eucalyptus, commonly called gums, includes 500 to 700 species and grows naturally in Australia and New Guinea. At the turn of the century, Murray red gums were planted in North County, particularly in Rancho Santa Fe, for use as railroad ties. Later judged unsuitable because their wood split, they remained unharvested and multiplied.

“Some eucalyptuses have diversified radically in several forms,” says Beauchamp. “The group as a whole has not been exploited here but some make excellent drought-tolerant plants.”

Other popular imports include the Peruvian pepper, commonly called California pepper; and the olive tree. The pepper originated in Peru and was one of the first trees cultivated at the California missions.

One venerable oldster, which was probably planted in the 1820s, still stands in the garden at the Mission San Luis Rey de Francia. Olive trees hail from Europe but make fine, hardy specimens.

The pepper and one species of eucalyptus as well as the native torrey pine have been included in the city of Carlsbad’s tree give-away program, which was established to encourage the planting of trees.

Five-gallon containers, one for each household, are available at the Carlsbad Department of Parks and Recreation office at 1166 Elm Ave. from 8 a.m. to 4:30 p.m. during the week. The program will probably run until the end of March.

“We’ve been planning this since last year, and may purchase as many as 1,000 trees,” says Fred Burnell, tree supervisor for the department. “We bought as many drought-tolerant trees as possible, but some are more so than others. In less than three days, people have picked up between 130 and 140 trees. We also give them a handbook on planting and tips on watering including recycling household water, putting in drip systems and building basins to catch water.”

While these trees may suffer only a bit, some “exotics” may be doomed without a helping hand. Beauchamp points to the handsome coral tree, with its thirst for water and soft wood, as a possible casualty.

Other trees to watch for signs of trouble include sycamores and some of the showier palms, says James Frommer of Landscape Resource Group. Some of the taller eucalyptus are also being hurt. As their roots become shallower in their search for water, they sometimes blow over when storms come.

Low allocations of water should force people to know what’s in their own yard,” says Frommer. “They can identify their trees by looking in garden books. Trees have to be in the forefront as the most important type of plant. They are expensive to replace and to remove, and time-consuming to grow.”

When precipitation returns to closer to normal levels, many landscapers and other plant experts hope for a new look at garden design. Even record rainfall cannot change the fact that this is a dry climate, outside sources of water are limited and human population continues to grow dramatically.

Instead of planting huge expanses of shallow-rooted grasses surrounded by trees and flowers, one option discussed by a growing number of Southern California landscape architects is a garden that would be at home in similar Mediterranean-type climates. These gardens may have small areas of lawn, but would be broken up by paths, different kinds of rock, and plantings of native shrubs, trees, perennials and ground covers.

Another change may be away from what Beauchamp calls the need for instant gratification.

When we put in plants that have been in 15-gallon containers, we create something like a caged animal that must be fed constantly. Instead, he and others recommend starting plants from seeds or cuttings and getting back to the “real joy of horticulture.”

“There’s a popular misconception that oaks, for instance, are slow-growing, but young trees aren’t,” says Vincent Lazaneo, an adviser with the University of California Cooperative Extension.

“If acorns are collected and planted directly in the ground in the fall, protected with chicken wire, and allowed to germinate through winter, you can end up with a 30-foot tree in just 10 years,” he says.

The San Diego Chapter of the American Society of Landscape Architects stresses that the lessons learned during the drought need to be remembered when it has passed: “We must permanently sensitize ourselves to the necessity of water conservation; conservation, not only of water, but of all resources, must become a way of life.”

Conservation needn’t guarantee a bleak, colorless environment though.

As Carole Ottesen points out in her book “The New American Garden,” we’ve been installing the same old landscape, borrowed from England, for well over 200 years. By so doing, we’ve established a “rigid conformity to lawn and shrubbery that ignored the unique flora, fauna, and climates of the American continent.”

Perhaps the North County gardens of the future will be designed with that uniqueness in mind.