Callery pears, also known as flowering or ornamental pears, produce attractive fall color, as well as profuse white flowers in spring.

Photograph by Shari Kaplan

Autumn colors differ each year and from tree to tree

One of the many benefits of mild weather in the Santa Clara Valley is that autumn color stays on trees much longer than it would in more wintry or snowy weather. Some of my colleagues in Wisconsin, Pennsylvania and western Kentucky find it difficult to believe that sweetgum (liquidambar) trees here may hold their foliage through December. Some sweetgums even carry it through winter, to be replaced by new foliage in spring.

New England displays the most impressive autumn color in the world. Color in California is mainly limited to urban areas and to a minority of all the species of trees commonly used in landscaping. Most deciduous native trees merely turn brown and drop their foliage in autumn or winter. The bigleaf maple (a.k.a. Pacific maple) and various species of cottonwoods exhibit good yellow color, but are usually mixed with other trees that are not colorful. However, the trees that color well are still on display when New England is covered in snow.

Each species of tree grown for autumn color responds differently to various weather patterns. This year, Chinese pistache, sweetgums and ornamental pears colored very well; but birches, red oaks and several species of maple did not. Each tree has good years and bad years. Gingkos, however, always seem to have good years.

Each species also displays particular colors. Gingkos, birches and poplars are always yellow. Red maples are always red. Red oaks and pears may be red or orange. Some find the purplish red of the Raywood ash to be interesting. Sweetgums and a few other species display a wide range of color that varies each year. Sweetgums may display burgundy color, which some garden enthusiasts do not find appealing. Incidentally, trees grown from seed are more variable than are trees of the same cultivar.

Deciduous conifers are rare and almost exclusively display brown color. (Gingko is actually classified as a conifer, but only turns brown if dead). Consequently, deciduous conifers are normally only planted by those who enjoy exotic species, and not so much for their color. Those of us who appreciate them find the rare specimens very impressive. Those who do not appreciate them often mistake them for dead.

Not all deciduous trees exhibit good autumn color and some even appear rather scruffy. London plane trees (a type of sycamore) begin to yellow in late summer, but never turn bright yellow. Rather, they grow powdery mildew, brown around the edges and fall, often while still partly green. Valley oaks, which are awesome in all other respects, go dormant when weather turns cold, but only drop their now dingy leaves if compelled to do so. Sudden cold or rain can cause most of them to fall early. Otherwise, they may drop slowly as they decay through winter.

Autumn color may be exhibited by a wide range of shrubbery and perennials, many of which are evergreen. Witch hazel and blueberries can be just as colorful as sweetgums. Heavenly bamboo (nandina) is most often planted for the lacy evergreen foliage, but will also turn color in cold weather. Boston ivy is a classic climbing vine.

When selecting plant species for autumn color, it is advisable to see the choices in their autumn colors. It is also important to know how each species behaves. For example, poplars are some of the best for bright yellow color, but are also among the most destructive trees and not well-suited to small urban gardens. When a selection is made, it is best to plant deciduous plant species when they are completely dormant in winter.

Tree of the Week: Callery pear

During the holiday season, many of us will be watching the callerys. That is not misspelled, but refers to the many callery pears, Pyrus calleryana, commonly planted in Santa Clara Valley. The callery is also known as ornamental pear, flowering pear, or very often by the cultivar names, such as Bradford pear or Aristocrat pear. They are very showy this time of year, and again in spring as they produce small but profuse white flowers.

They enjoy full sun and tolerate minimal irrigation once established. Well-behaved roots and shapely form are why this is such a popular street tree. The 2- to 3-inch long glossy leaves are very similar to those of fruiting pears. The Bradford cultivar has been the most popular for years, but the cultivar Aristocrat is becoming more popular. Aristocrat is much more shapely, with a distinctive vertical branching structure.

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Horticulturist Tony Tomeo can be contacted at 408.358.2574.

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