Deodar cedars, such as this one planted in Saratoga by local arborist Blair Glenn, are examples of nonnative trees that grow well in the mild Santa Clara Valley.

With help, nonnative plants flourish in Santa Clara Valley

By Tony Tomeo

There are several places in the world with climate similar to that of the Santa Clara Valley. There are also a few places with similar soil, and even a few with similar water quality. However, it is rare to find places remote from each other that have many similar qualities. What can be grown here and how it is grown is specific to this area.

Plant species best suited to gardening that are not native are imported from places with similar climates, such as Italy, Algeria, South Africa and Australia. Because many do not originate in areas with similar soil types, special adaptations are often necessary. For example, many cedars from the Mediterranean thrive in the Santa Clara Valley climate. However, they often experience problems with drainage, since they prefer rocky soil similar to that of their native regions.

Fortunately, mild climates such as ours are also more conducive to gardening with not such well-suited species. With soil modification and proper irrigation, plant species that would not normally grow here may be used successfully, although not as commonly. Even species from high mountains or desert areas may be imported for garden use.

"Ornamentals" are not commonly derived from such harsh environments because these species are often too specialized to be of ornamental or functional value. Many are too small or grow too slowly to be effective in typical landscapes. Garden enthusiasts who enjoy collecting these unusual species often construct rock gardens to keep them happy and to display them separately from other styles of landscapes.

Rock gardens were actually developed in Europe to provide homes for unusual species, known as "Alpines" because they were collected from high elevations in the Alps. Such gardens may also feature plants collected from moraines (glacial deposits) or scree (broken rock that accumulates at the bottom of cliffs or steep mountains).

Western (North American) rock gardens are more likely to include a wider range of plant species. Perennials from southwestern deserts or the Rocky Mountains are more common than Alpines. The dryer and warmer but mild climate are also suitable for desert plants from other continents. Landscape style is also distinctively western. They may be large enough to fill an entire garden, or small enough to fit in an atrium.

It is important to remember that rock gardens are not simply constructed to landscape overly exposed areas. The worst are those between the sidewalk and street, surrounded by pavement. I find that such landscaping enhances the inhospitable nature of the space. Rather, rock gardens should be constructed where the small plants within them may be enjoyed in a more usable part of the garden. It is also important to emphasize the plants in the garden and not the rocks. Although rocks generally enhance the appearance of the garden, their primary function is to provide the plants with growing conditions similar to those in their respective natural environments.

One main requirement of rock gardens is very good drainage. Classic rock gardens are often planted in thin layers of loamy soil over coarse gravel or pulverized concrete. Because most plants originate in deserts or high mountains, they are accustomed to growing with minimal soil. Most rock gardens are installed with almost full sun exposure. However, there are many species conducive to rock garden culture that will tolerate some degree of shade. Planting on a slope or terraces is more effective for displaying low-growing plants.

Cacti and succulents have traditionally been popular; however, many other perennials and even dwarf trees are also suitable. Light shade trees or bamboo may be included if sun exposure is too intense. In rock gardens, sculpture may be effectively displayed more appropriately than in most other styles of landscapes.

Tree of the Week: Deodar cedar

Unlike most cedars, which originated around the Mediterranean Sea, the deodar cedar, Cedrus deodara, is native to the Himalayas. It is fast growing when young and will eventually reach 60 feet tall with potential for a 30-foot spread. If planted in a large area, limbs may be left at ground level. Otherwise, limbs may be pruned up to a sufficient height to use the area within the dripline. Foliage consists of small, fine tufts of bluish needles. Deodar cedars are very drought tolerant. In dense soil, they prefer infrequent irrigation after the first few years; otherwise root problems may develop. With the exception of a few cultivars, they are grown from seed and may exhibit genetic variability.

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Horticulturist Tony Tomeo can be contacted at 408.358.2574.

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