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Monday, November 5, 2012

Cottonwoods (Poplars) Not a Good Choice for the Desert

Poplar or cottonwood growing in desert
landscape. It is difficult to water these
types of trees in our climate due to their high
water demand and our irrigation systems not
intended for very large, high water-demand trees.
Bob, I have 2 cottonwood trees that are about 15yrs old. They were doing very well until about 2 years ago. At that time I noticed a limb here and there dying. Now more and more are dying off. I cut off a limb that broke in the wind recently that was partially dead at the top. I saw bugs in the area that was dying. The bark turns brown and peels off the limbs that are dying. Also when I cut off limbs that are dead or dying the wood under the bark is turning a dark brown at the center. I found info on the internet that recommended using a pesticide applied to the soil along with a 10-10-10 fertilizer mix. I just did this last week so I don’t know if this will help. What do you recommend? What do you think is the problem? Am I doing the right thing? What do you suggest?

I really appreciate your help. It would be a shame to lose these beautiful trees.

Cottonwood trees require lots and lots of water. I hope these are not growing in a rock or desert landscape or you will have problems. If you will be successful they should be growing in a large turfgrass area with you supplying supplemental water to them deeply twice a month. This means not only are they receiving water from the lawn, but you would be watering them with extra water down to a depth of 18 to 24 inches twice a month during the growing season. The area that you are watering under the tree should be approximately the same area that is under the canopy or spread of the tree.

It is hard to judge but my guess would be that you are getting branch dieback from a lack of total water applied to the tree. These trees will not survive for any length of time if they are in drip irrigation. I would highly recommend that these trees be watered with a bubbler that releases large amounts of water quickly into a basin beneath the tree. This basin should be the size I mentioned above.

I don't believe that there is anything wrong with this tree that lots of water applied under the canopy would not cure. Watering schedule during the summer months would be every 2 to 3 days. The frequency of applied water decreases in the cooler months but the volume of water applied remains the same... that water needs to travel in the soil to a depth of 18 to 24 inches beneath the tree.

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