July 9, 2011

1 - Symptoms of winter cold and now drought are showing up in trees. Proper watering is critical to tree survival.

Yard and Garden - July 9, 2011


We live in Sandia Heights here in Northeast Albuquerque. In May I realized that our mature ash and red bud trees had more dead limbs than usual, and now, I see that one of our cottonwoods has a lot of yellow leaves which are beginning to fall as if it were autumn. Otherwise, the trees seem healthy. I have been leaving a soaker hose around their bases for the last month or so because I thought that they were not getting enough water due to the drought. Do you think that is their problem and can they be saved by using soaker hoses or is it too late for them? We'd appreciate your thoughts/advice. Thanks.

- Sidney A.



Gardeners in all parts of New Mexico are trying to distinguish between damage done by the extreme cold last winter and the drought this spring. It is likely that both environmental stresses are responsible. The most common question this year has been regarding removal of dead branches. Many of the dead branches are due to the severely cold winter, but some of the symptoms you are describing are probably due to the drought. Branches that never produced leaves or produced unhealthy growth in the early spring were probably damaged by the cold. Those that did produce leaves which are now dropping are probably responding to the drought.

You can safely remove winter damaged branches now in the summer. These dead and damaged branches are much easier to identify for removal while the other branches have leaves. Those branches that are dropping leaves now, but are otherwise healthy should be retained at this time. You can always prune them later.

Irrigation is very important at this time and a good monsoon season is badly needed. Proper irrigation may be difficult. Tree roots extend over a large area to exploit the water and nutrients needed to support a large tree. These roots extend at least 4 times the height of the tree from the tree. The roots that most effectively absorb water and nutrients are the smallest roots. These absorptive roots are most numerous at the dripline and outward to the full extent of the root system. Irrigation near the trunk (inside the dripline) is not effective. Irrigation only at the drip line will be more effective, but may not provide enough moisture to prevent loss of leaves and some twig death. It would be ideal if water could be applied to the whole region of absorptive roots, but this is often impractical and in times of water deficits it is unwise.

Your goal will be to provide enough water to sustain your trees until more normal moisture returns, even if some leaves, twigs, and smaller branches must be sacrificed. To accomplish this, apply water at the dripline and outward for several feet. Provide enough water to moisten the soil to a depth of at least 2 feet. In your sandy soil you should water again every 2 weeks. Gardeners with more clay in their soil may be able to sustain their tree by watering once every 3 to 4 weeks. Always moisten the soil to the same depth because roots become dependent on your irrigation and inconsistent irrigation can result in loss of roots and root rotting. When the monsoon rains come, continue to irrigate the trees to the same depth at the same intervals. You should reduce the quantity of water applied to compensate for the rain water, but the soil should be moistened at least to a depth of 2 feet.

If you are successful in sustaining your trees, even if there is some dieback, the trees will be able to replace the portions lost to dieback and, perhaps, increase in size. You may also want to consider replacing any trees that are severely damaged with trees better adapted to your very dry, sandy location. Cottonwood trees should be growing in areas that are more consistently moist than your site. The ash trees may succumb to insects following the stresses they are experiencing. They also prefer a more consistently moist location.

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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