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Wednesday, October 11, 2017

"Evergreen" Palo Verde Leaves Turned Brown

Q. We have several different Palo Verde trees.  Last winter one had brown leaves and looked like it was dying. Come spring, it grew new green leaves and looked fine during the summer.  This winter again several of them have brown, dead-looking leaves.  What is going on?
Is this Palo Verde tree dead?, The winter temperatures got cold enough to kill the leaves but not the tree. The leaves died and dropped from the tree.
A.  Sometimes Palo Verde are called evergreen when, in fact, they may not be in our climate.  Evergreen in a warm climate may not be evergreen in a colder climate.  Whether they keep their leaves green through the winter is a matter of climate, weather conditions, the type of tree and how the tree is managed.  
Palo Verde trees can get quite large as this native tree in Arizona can testify.

            Just because they are collectively called Palo Verde does not mean they respond to winter cold temperatures the same.  Some types of Palo Verde may be evergreen during warm winters but brown leaves or drop them during cold winters.  Some types of Palo Verde trees maintain their leaves through the winter better than others.  Therefore, you’re seeing differences among the several types you have.
A multi-branched Palo Verde can be a beautiful addition to a desert landscape.
            If winter temperatures are warm, the leaves remain green or evergreen.  During colder winters, leaves fade to a yellowish green after a moderate cold snap.  If winter temperatures get colder, leaves die and turn brown.  They may or may not drop.  Don’t worry.  New leaves emerge in the spring and replace the dead ones, just as yours did.
Flowers of Palo Verde are quite beautiful as in this Parkinsonia but they also shed a lot of pollen which can make life unpleasant for people with allergies.
            At temperatures, even colder than this, leaves as well as small branches might die. Temperatures still colder?  Leaves and small branches die and larger limbs might die as well. Temperatures even colder than this?  The tree might die.  How much of the tree dies depends on how cold it gets and for how long this cold temperature sticks around.
            Help trees that are winter tender by NEVER fertilizing with nitrogen fertilizers after July 1st.  Applications of phosphorus or potassium are fine, but no nitrogen.

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