October 15, 2016

1 - In dry times, proper placement of water is critical for sustaining landscape trees until rains return.

Yard and Garden October 15, 2016


The trees around our home are not doing well this year. Some are 100 year old elms. It has been a very dry year, but I have never seen the elms doing so poorly. We do water near the base of the trees as often as possible and we try to maintain the grass in the lawn. The trees produced leaves in the spring, then at the top of some of the trees the leaves turned yellow and fell early while other leaves are still green. Our pines, junipers, and a spruce are not doing well either. The needles have pretty much fallen from the top one-third of the spruce tree.

- B.C.

Harding County, north of Roy


Your comment about being a dry year provided some direction for me. I checked the CoCoRHaS - New Mexico Map to see what the precipitation was like in your area. Unfortunately, there are no volunteers reporting the precipitation near you (nearest was Logan). I have seen the grasses near you and observed that you are in a really dry location. Toward Wagon Mound the grasses looked pretty good, but in your area the grass is very sparse. It has been really dry in your area and that may be a large part of the problem.

There could be other factors involved, especially in the case of the spruce tree, so I recommend samples be taken to your local NMSU County Cooperative Extension Service office. Samples of healthy and not healthy (but not dead) parts of the trees can be sent by your Extension Service agent to the NMSU Plant Diagnostic Laboratory in Las Cruces to see if there are insect or disease problems involved. When trees are stressed by the environment, they become more subject to other problems, so it is wise to send the samples.

However, the drought is a very likely primary cause of the problems. In years such as this year, proper irrigation becomes extremely important. Irrigation water for the trees should be applied to the soil at their dripline (soil under the farthest extent of their branches) and beyond as far as possible. The roots between the tree's trunk and the dripline are large pipe-roots that absorb little water. Roots under the dripline and farther out are smaller roots with numerous very tiny root hairs and hair roots. These are the absorbing roots and the target for irrigation. Irrigating the lawn helps, but grass is a very efficient scavenger of water and reduces the water available to the trees. Watering once every two weeks enough to moisten the soil to a depth of approximately 3 feet (sometimes a little more deeply to prevent accumulation of mineral salts that can injure roots).

This irrigation frequency may not be enough to sustain the lawn in a healthy condition, but a lawn is much easier to reestablish after a drought than 100 year old trees. Another factor to consider in years such as this is that your primary purpose is to sustain the trees rather than have them prosper if irrigation water is limited. There may be some die-back in the trees, but if they receive enough water, they will be alive and ready to grow in years with increased precipitation.

Another factor to consider is that trees in a landscape area that have been irrigated through the years become dependent on the irrigation and may suffer more in dry years than some trees away from the landscape where they are less dependent on irrigation. Since the trees are dependent on you, you must provide water, even if only enough to just barely sustain their lives until the rains return.

Oh, yes, if any readers of Yard and Garden in the Northeastern part of New Mexico (or for that matter elsewhere) are willing to volunteer to report precipitation to the CoCoRHaS project, you can find information about becoming a volunteer at COCORAHS. Your participation will be greatly appreciated, especially in areas with few reporters.

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.


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

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