Issue: April 30, 2005

Correction: Critical Root Radius | Sunburned Palm Trees

Correction: Critical Root Radius


I read your recent column about critical root radius and would like to pass that information along to our producers in the New Mexico Organic Commodity Commission but am confused about the formula. I don't understand how the figures of 84-126 feet are reached from multiplying 7 feet by 1 or 1.5. I would sure appreciate clarification on this.

J. Quinn


Thank you for your interest and for bringing this to my attention. The reason for the confusion is that I omitted two critical words from my article about the critical root radius of trees (how far to stay from trees when excavating). The proper statement is "The critical root radius is the diameter (in inches) at 4.5 feet above ground, multiplied by either 1.0 or 1.5. That omission was critical. The calculations with coefficients of 1.0 and 1.5 are:

7 feet X 12 inches/foot = 84 inches X 1.0 (feet/inch) = 84 feet Critical Root Radius
- OR -
7 feet X 12 inches/foot= 84 inches X 1.5 (feet/inch) = 126 feet Critical Root Radius

Thank you for reporting my error so that I can correct it.

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Sunburned Palm Trees


I have a couple of larger palms, but I have forgotten what kind. They always seemed to get sunburned when outside in the summer, so I considered them indoor/shade palms. I wanted to buy a palm (like those I see in Las Cruces) to plant outside. I went to a garden center, and they had palms that looked like those I wanted. They were labeled Canary Island. I took one home and noticed that it sure seems to look like those I've had in pots for years. The instructions said "full sun". I'm wondering "que pasa"?


The factor that I think is most relevant in your situation is that Las Cruces full sun is not the same as full sun in many other places. Our high, dry environment increases solar intensity and exposure to ultraviolet radiation. Both the elevation and lower moisture content of the air can contribute to the burning of the plants. The lower elevation along the coast of the Canary Islands provides a much thicker column of air that contains more moisture between the sun and the plants, so they are not exposed to nearly as intense sunlight as plants in Las Cruces.

Other things to consider are salt accumulation in the soil (high calcium salt and other salt levels are common in New Mexico). Excess drying can increase the salt concentration around the roots, resulting is salt burn in the leaves (browning around the edges and at the tips of the leaves).

The new palm may or may not be the same species as your old one. Many palms look the same even when they are quite different. You need to know what characteristics to look at when separating species.

Be careful in your selection because not all the palms sold in some garden centers will be winter hardy. The term "Canary Island" worries me because I don't think they will be adapted to the cold, dry winters in New Mexico if they are from the Canary Islands. The Canary Islands are at about 28 degrees north latitude and surrounded by the moderating influence of the Atlantic Ocean whereas Las Cruces is at 32 degrees north latitude in the middle of a continental land mass. Las Cruces will be much colder.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook.

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