Most people who read my columns are garden enthusiasts and probably perform most or all of the work in their gardens. However, when large trees need attention, it is necessary to have the work done by experts.

Those of us with maintenance gardeners have probably had problems at one time or another (probably involving hedge shears). Most species in the garden eventually recover from such abuse or can be replaced. However, when working with large trees, improper maintenance procedures can be much more damaging and difficult to correct. Replacement is certainly not as simple as for other plants, since the changes in sun exposure affect many other plants in the area normally shaded by the removed tree. Removal can also be a considerable expense.

As with gardeners or other horticultural “professionals”, good arborists (horticulturist who specialize in tree care) are difficult to find. Fortunately, the few good ones are exceptionally good. If fact, in my opinion, the best in the state are right here in western Santa Clara County. Because trees are usually the most important investment in a landscape, it is important to be able to recognize a qualified arborist when tree work becomes necessary.

The International Society of Arboriculture (ISA), an organization dedicated to the promotion of professionalism in the various tree care industries, is very helpful with distinguishing good arborists. Those who are recognized by the ISA as certified arborist have past a series of tests relevant to their expertise. Certification also indicates more than successful completion of the exam. It shows that an arborist takes his work seriously enough to be involved with the ISA, which is an effective means with which to stay in contact with other professionals and to exchange information. Although I can not say enough good things about the ISA in this short column, I do recommend businesses which are supervised by ISA certified arborists. Incidentally, I’m a Certified Arborist with certification number WE5197A.

The American Society of Consulting Arborists (ASCA) is also a great organization for the dedication of providing comprehensive tree care diagnosis.

I am perhaps too critical of arborists, but I also prefer those who know their trees. Those who know the differences between species (and can speak the Latin to prove it) have obviously done their homework. Those who think redwoods, pines, firs, spruce, cedars and cypress are all the same thing should be avoided like Rhus diversiloba (poison oak). And yes, there are some out there.

Of course if removing trees, certification is not so important. Even I can cut down small trees. However, it best to know that whoever does the work can do it safely without crushing surrounding plants, fences or the neighbors Buick. With any tree work, insurance should be required. Smaller companies that might be questioned often advertise that they are bonded and insured; otherwise, you might want to ask.

It is not common to ask arborists for references, but many are well known for their reputations of quality work. Some of the best may be found by asking friends and neighbors about who maintains their trees, especially if they have been satisfied with the work for a few years or more. Those who do bad work, or “hackers”, are usually not around long.

If it is necessary to find someone to perform tree work in the telephone directory or newspaper, those who promote procedures which are not horticulturaly correct, such as topping, have no business in your garden. Real arborists work by the rules.

I also find that those who advertise too many other services are not specialized enough. Wood chips, firewood and stump grinding services are acceptable. However, those who build fences, decks, ponds or irrigation systems or haul trash are too diversified to be full time arborists, dedicated to their work. Advertisement of low rates should also be a concern. It is best to spend more for good work than save a bit only to spend considerably more on repair or even removal of a damaged tree.