Q. I have several xylosma trees near my pool, approximately 8 feet away. My neighbor thinks they are related to ficus, which have a very bad reputation for aggressive root systems and pool destruction. Any help would be appreciated.

A. Xylosmas are usually sold at nurseries as bushes and shrubs. If left untrimmed, however, they are quick to grow into small trees 15 to 20 feet in height. They are actually in the willow family, not the ficus family. Xylosmas do not have aggressive root tendencies like ficus do, but you should always be aware of the potential for damage by any tree roots near a pool deck. No guarantees here, but if I had a xylosma 8 feet away I wouldn't lose any sleep over it, but that's just me.

Q. I really love my birch trees and want to keep them healthy. I had them thinned four to five years ago and think it is past time to do so again. I've heard that birch trees should never be topped. Is that true? My gardener wants to top them, but he is not an arborist. What is your opinion?

A. There is rarely a good reason to top a tree, any tree. If the top of a tree is dead or damaged, of course have the top trimmed off. If a tree has a serious lean to one side but is otherwise in good health, then trimming off some of the excess weight at the top may actually save the tree. Under normal circumstances, though, if the tree is healthy and doing well, don't let anyone top it for any of their reasons. The short answer is, "Don't top your trees." That's the opinion of me and every other competent certified arborist.

I have talked about this before, but it is good to reiterate from time to time. There are only three good reasons to trim any tree: safety, health and aesthetics. Ask yourself why you want to trim this tree. Is it a fairly safe tree? If it is a birch tree, it probably is. Is it healthy? Well, if the leaves are green and the canopy is full, then it is thriving and happy. Is the tree aesthetically pleasing? If the answer to all of these questions is yes, then the next time you see your gardener tell him to mow the grass, pull the weeds and leave your trees alone. But say it with a smile.

When you need your trees trimmed use a certified arborist. Having a professional arborist trim them correctly will cost more, but you will get what you pay for, and your trees will love you for it.

I get tired of seeing trees that used to be 30 feet tall and are now 15 feet tall because some gardener thought they were too tall. When I drive by some scraggly, butchered scarecrow of a tree that last week was tall, green and swaying in the breeze, creating shade for the house and kids, habitat for the birds and squirrels, and oxygen for our world, I find myself shaking my head and muttering, "Why, why?"

David D. Mortimer is a certified arborist with more than 30 years experience in the tree care industry. E-mail questions to dmortimer@theacorn.com.