I don't know what species inhabits Middle Earth or how they became disfigured, but those at San Francisco's City Hall have been pollarded for many years. Pollarding, simply defined, is very severe pruning. The proper technique was developed centuries ago either to provide canes for willow baskets or to confine otherwise large trees in small gardens.

I can only think of one of my colleagues who is not aghast that I do not condemn pollarding. This is because it is almost never done properly and is consequently very detrimental to the health and structural integrity of the victim trees. Done correctly, however, pollarded trees can be maintained as long as trees that are not pollarded. I just don't understand why anyone would want to do it when baskets are so cheap and when so many trees that do not become large are available.

First of all, pollarding is not for every species. In fact, only a few are conducive to this extreme procedure. Secondly, it can only be performed during winter, not only because the subject trees are dormant, but also because solar radiation is inhibited during shorter days when the sun is lower in the sky. If shaded limbs suddenly become exposed to sunlight during summer, they are easily damaged by sunscald.

Trees cannot be pollarded for the first time when mature because the resulting large wounds cannot adequately compartmentalize (heal) before decay extends into the affected limbs. Pollarding must begin when trees are still somewhat young and must be repeated every winter afterwards. Restoration of a natural branch structure after pollarding is possible among many trees, but requires many years of thinning and pruning to compensate for severely compromised structural integrity.

During the first pollarding procedure, few or many of the best-structured limbs that are well distributed throughout the canopy should be selected and preserved as other limbs and stems are removed completely. The preserved limbs may then be pruned to a desired length. Additional structural limbs may be likewise preserved during the first few subsequent winters, but all growth that has emerged after the first pollarding procedure is otherwise removed every winter.

Traditional and "proper" pollarding allows preservation of the basal few inches of one or two of the secondary stems that are oriented toward any preferred direction. Most of the secondary growth will emerge from the distal end of the stems, and some will emerge from the "knuckles" that were distal ends during previous years.

Because more Americanized pollarding removes all new growth, each main limb terminates at a single knuckle that eventually becomes quite distended. Either form of pollarding works because the many small wounds are easily compartmentalized every year before decay can extend into the supportive limbs and because new growth emerges and provides shade for main limbs before they can be damaged by sunscald.

Tree of the Week:
Digger pine

I don't often discuss esoteric species that are enjoyed by only a few garden enthusiasts, but this picture taken near the summit of snowy Mount Hamilton was simply too artistic to be ignored. It could be a Coulter pine or ponderosa pine, but I think it is a Digger pine, Pinus sabiniana, because there were so many mature specimens within the same area.

Needles of all three species are in bundles of three, and those of the Digger pine are somewhat gray and slightly longer, approximately 10 or 11 inches long. The dark brown cones are approximately 8 inches long. Trunks are bare for a considerable height and branch repeatedly at sharp angles into several leaders. The rounded foliar canopies are sparse and may be as high as 80 feet and as broad as 40 feet. Digger pines can only be accommodated by large gardens, and only if irrigation is very limited.

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