Even with the best care, old oaks that predate development are particularly susceptible to decay because of severe environmental changes. For example, the oaks we recently inspected are well cared for now, but the roots of most have been damaged by excavation during development of the site in 1978, when the vulnerability of such trees was not common knowledge. Most damage was likely initiated even prior to that when the trees were subjected to orchard culture, which included tilling and irrigation. Such environmental changes are difficult to accept after a few centuries without disturbance.

Damaged roots are more susceptible than nondamaged roots to decay, and the decay proliferates if the area is irrigated. This decay continues to damage the affected root systems and eventually extends into the main trunk and limbs. This is a natural process of aging, but it is enhanced by root disturbance and irrigation. Even trees in the wild that have not experienced substantial environmental changes eventually succumb to decay after a few centuries.

As trunks and limbs succumb to decay, they become more susceptible to fracture. Ironically, healthy trees are more susceptible to fracture than unhealthy trees that are similarly decayed. This is because dense foliar canopies are heavier and have more resistance to wind than sparse canopies. Of course, most of the weight of some of the oldest and largest trees is within the wood rather than the canopy.

Branch structure is also relevant to fracture susceptibility. Limbs that extend far (horizontally) from the origin exert considerably more leverage than shorter or more vertical limbs. Very acutely narrow unions often have "included bark" that becomes compressed between the two affected limbs that cannot form a union through it.

The International Society of Arboriculture I so frequently discuss as a source of contact information for certified arborists is also a good source of information concerning maintenance of trees, including old oaks. I certainly recommend visiting its educational website at www.isa-arbor.com.

Flower of the Week:
Blue marguerite

There is, of course, no need for any flower to be attractive to a mate. Instead, flowers attract their "pollinators of choice." Those that rely on wind may not be as visually interesting, but are profuse and produce copious pollen. Others use fragrance, color, texture and even flavor (nectar) to stimulate four of the five senses of their favorite pollinators, such as bees, butterflies, flies, bats, hummingbirds, ants and a few others.

Pollinators that rely on color to find flowers seem to prefer yellow, orange and red as well as wavelengths of light that only they can see, which is why purple, blue and green flowers are not as common. Among the blue flowers, most are somewhat purplish. Very few are "true blue."

Flowers of the blue marguerite, Felicia amelloides, have clear yellow centers, but the petals are about as blue as the sky. In fact, with the exception of a rare white-blooming variety, floral color among the various varieties only ranges from dark blue to light blue. The flowers, which bloom most profusely in June, are usually slightly wider than an inch, but a few varieties produce larger flowers that are wider than 2 inches. Bloom may be continuous except during the coldest winter weather.

Blue marguerite is happiest in a sunny location with regular irrigation and may eventually be as wide as 4 feet and slightly more than a foot deep. The upper surfaces of the inch-long oval leaves have a slightly raspy texture. Aggressive shearing near the end of summer promotes denser growth and more profuse bloom.

Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.