1 - In prolonged dry periods, trees in all parts of New Mexico need irrigation, but they must be irrigated properly.

Yard and Garden May 11, 2013

Q.

I wish you would stress the need to water trees. We are seeing so many dying trees in Roswell this year. This is occurring in poorly managed landscapes, but also in well cared for landscapes. It distresses me to see a tree dying. Some people seem to think trees can get along all by themselves. We have had a long dry spell that has damaged everything, especially the trees.

Laverne S.

Roswell

A.

You are correct, and the problem is not limited to Roswell or the eastern part of New Mexico. This problem is wide-spread throughout the state.

As you mentioned, in some parts of New Mexico trees can often survive without irrigation, gardeners do not think to water their trees. When precipitation is reduced for an extended period of time as we are now experiencing, the trees must be irrigated or they will be injured, perhaps to the point of death.

In some cases people irrigate their trees, but not properly. Gardeners who irrigate their trees at the base of the trunk are putting the water in a place where the tree may not be able to use it. The large roots under the canopy of a tree do not absorb much water; they carry water from the small, absorbing roots, to the trunk which then delivers the water to the leaves. There are absorptive roots in the soil under the dripline of the tree. This makes sense since the name "dripline" indicates that this is where water drips from the ends of branches to the ground during a rain. It is drier under the leaf canopy because the tree redirects water to the dripline. Because of this, the soil under the dripline of a tree is an important place to irrigate a tree. However, the roots of a tree extend well beyond the ends of the branches and should be irrigated. Tree roots can extend 4 or more times the height of a tree from the trunk. It is not necessary to water the entire extent of the root zone, but a significant portion of the root zone should be irrigated.

Trees that have been on their own without irrigation may have much more extensive root systems than trees that have been regularly irrigated. This is because roots will adapt to irrigation when the trees are irrigated on a regular basis. The root system of such trees will be most developed in areas where water is regularly available to the tree. Regularly watered tree roots may not extend as far from the trunk and dripline and will be easier to maintain during extended periods of drought.

During times of drought, irrigation of trees is necessary, but this must be done properly. Improper irrigation is a waste of limited water. Times of limited precipitation may encourage New Mexico gardeners to look for trees, shrubs, and other landscape plants that require less water.

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: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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