Ask the Arborist

Q. Several European white birch trees of mine have died. I still have others. What can you tell me about this situation?

A. Birch trees are native to many areas of the world. There are Red River birch that inhabit the eastern part of the United States and white paper birch that grow in the northern areas of this country and Canada. Some birch species are native to Japan, China, India and Europe. Regardless of where they come from, birch trees have one thing in common: They like plenty of water.

The native habitat of most birch trees has a richer, more acidic soil than what's found in Conejo Valley. We're basically living in a desert and asking these trees to grow in an environment that's foreign to them. Most of the thriving birch trees I've seen are in a green, well-watered lawn or in some other area that receives regular irrigation. If birch trees don't get ample amounts of water, they eventually go into a downward health spiral that begins with the thinning of the crown, dead branches and eventually death.

For the remaining birch trees in your yard, I would suggest you improve the conditions around them. Fertilize each tree by poking about six 1inchdiameter holes 12 inches deep within the drip line area of each tree. Fill the holes with any good lawn fertilizer, the more nitrogen content the better, and water the area well.

Then, especially throughout the summer, continue to give your trees ample amounts of water. You don't want to turn the area around the tree into a swamp, but you don't want it bone dry either. The goal is to saturate the soil in the drip line area to at least 12 inches deep about every two weeks.

Q. Sue writes, "Can you please tell me if the roots of a palm tree can spread and affect the walls of a pool? It is planted approximately 6 feet from my pool."

A. Palm roots don't develop in the same way that the roots of traditional trees like eucalyptus, ash or oak do. Those hundreds of small things you see bulging out at the base of a palm are the roots, and even though they spread out away from the trunk, they're usually smaller than the diameter of a pencil and remain fibrous and pliable. As palms grow, they don't increase in diameter, only in height.

The only potential problem I can see might arise if the pool or the deck around it is already cracked. That could create a consistent wet spot in the soil underneath it that could encourage roots from any kind of tree to get under the concrete and do some damage. But if you're concerned about palm roots pushing and cracking your pool, I wouldn't worry about that happening. Six feet should be far enough.

David D. Mortimer is a certified arborist with more than

30 years' experience in the

tree care industry. Email questions to dmortimer@theacorn.com.

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