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Arizona Cypress in the Owens Valley

Arizona Cypress

Arizona cypress growing in nursery (Photo by J Rutter)
The Arizona cypress (Hesperocyparis arizonica, Cupressus arizonica) is a common landscape tree in the Owens Valley. 

Arizona cypresses are evergreen conifers. They lack needles, but instead have grayish scales. Gray foliage varieties are more common, but there are many the look more green. In our area they can grow up to 45 feet tall, but they are usually shorter than that for reasons discussed below. 

Locally, many trees were planted in the late 1970s and throughout the 1980s. They were cheap, evergreen, attractive and promised to survive in our desert conditions. Having Arizona in the name made them sound even more suitable for our area. 

While some wonderful individual specimens of Arizona cypress are found planted throughout the valley, the most common use of this species was planting in rows, particularly as windbreaks or along driveways. This means that most Arizona cypresses are planted in large numbers so if something goes wrong, it does so in a dramatic way!

Gray foliage form of Arizona cypress (Photo J. Ruter)
Aside of a tendency to be a fire-prone species, the Arizona cypress is not a bad tree. In fact it is well-adapted to Owens Valley landscapes. There now many improved varieties available in the nursery trade, a far different situation from when most local trees were planted. Here is some information about the species from USDA.

Our local problems with Arizona cypresses are a result of how this species was used and cared for over the past 3 decades in our landscapes.

This page has information on why these trees are dying, and how to keep them alive.

Why Are They Dying?

Along the entire length of the Owens Valley you can find dead or dying Arizona cypress trees. They are easy to find since there are usually a dozen or more trees all in various states of distress. 

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Arizona cypresses planted as individual specimens as part of a irrigated landscape seem to be doing fine. Trees planted in rows for windbreaks, visual screens next to buildings, or to line driveways are usually the ones we see dying.

These trees are dying as a result of prolonged stress. 

In almost every case, the trees were planted too close together. While the trees were young everything was fine. As the trees aged their space and water needs increased. 

Irrigation was always applied beginning from when they were planted, or else they would have died almost immediately. The problem is a combination of not meeting the increased water needs as a plant grows, along with the ever-growing competition with its neighbors for resources. Simply, the amount of water and care provided did not keep pace with each tree's needs.

A prolonged lack of water and resources creates stress. Stressed trees are susceptible to attacks by pests and pathogens. The widespread decline of Arizona cypress is a result of disease and insects caused by prolonged stress.

A good indicator of the stresses endured by these trees is their small stature. Trees 3 or 4 decades old should be much taller. Most trees I see are well under 30 feet tall, but many are closer to 20 feet in height. Stress slows growth rate.

Two main problems are observed in landscapes:

  1. Bark beetles
  2. Canker diseases

Both issues thrive in stressed trees. The close planting common here makes it easy for problems to spread along a long, uniform row of stressed plants. Of the 2 bark beetles appear to be more common.

How Do I Save My Arizona Cypress?

The key to preserving Arizona cypress in Owens Valley landscapes is to reduce stress. Healthy, vigorous trees are less prone to issues.

There are 3 steps you should take to improve your trees' chances:

  1. Remove any dead trees and branches.
  2. Remove trees to increase space between trees. This could mean removing every other tree...or more! Aim for mature trees to 10' to 15' apart. More is better. 
  3. Increase water. Aside of just applying water longer or more frequently, the area that you apply water should increase as well. The initial water berm used at planted is not adequate for a larger tree. At a minimum, the irrigated area should be wider than the drip line of the tree. More area is better. There are many ways to accomplish this (See irrigation page) but it is important. a 4-foot irrigation circle is inadequate over the long haul.

It may not be an option for you, but mulch can moderate stress and water loss in the roots. Wood chips work well for this purpose.

What about insecticides? 

There are insecticides meant to treat bark beetles. While they can be effective, it usually doesn't make economic sense to treat the large number trees that are usually under attack in your row. It may be worth treating a prized specimen, but unless you take care of the underlying problem of chronic stress, you will not ultimately be successful.

Information on homeowner insecticides used on bark beetles in California is available at this UC IPM page. (Spanish version.)