[Arid_gardener] Palo Verdes

[Tyler Storey]

Good morning Veronica,
You have witnessed one of the great truths of caring for trees: pruning
doesn't make trees smaller, it makes them bigger.  

What you describe sounds like the very common response that a Palo Verde
tree will have to being pruned: the formation of dead-looking brown "scar"
tissue around the cuts that ends up covering the branches and trunk.  Some
of it may also be a response to increased sun levels hitting the bark as a
result of the pruning, burning and killing the bark and resulting in the
same formation of brown tissue.  

A couple of things about pruning trees.  First, you say it was pruned a
couple of months ago, June or July, and unfortunately that may be the worst
time of year to prune a tree.  You'll have noticed that a Palo Verde has
very thin bark, really more like skin than what we think of as bark.  What
we tend to think of as bark, the rough brown scaly stuff we might see on an
oak, or pecan, ash, pistache, or pine, is made up of "dead" material, a
corky layer that forms the outside surface of the trunk or limbs.  That kind
of bark provides a protective surface for the tree, shading it from heat and
sun and the other elements.  A Palo Verde doesn't have that protective layer
for the most part, though it can develop with age.  

When a Palo Verde is pruned in the sun-intense Summer months, that delicate
green skin is suddenly exposed to elevated levels of direct Sun.  It becomes
damaged and responds by either dying or by producing the "scar tissue"
you're seeing now as a protective layer.  Additionally, you've probably
noticed that a lot of the brown stuff is around where it was cut during
pruning.  Same thing: the tree's response to fixing the injury it sustained
during pruning.  

The damage you see was caused by the pruning, through sun and die-back.
There is unfortunately no way to treat it.  

Now you also mentioned the trees are again in need of pruning.  You might
pause to reconsider.  Pruning, as you noticed, stimulates new growth.  New
growth makes the tree larger.  Larger trees may need more pruning.  You may
be embarking on a never-ending cycle that is going to result in these
beautiful trees that enhance your landscape becoming a high-maintenance
pain-in-the-neck covered with scaly brown stuff from top to bottom.  

Always stop to ask yourself "why?" before you prune.  A large tree is
generally a good thing.  They cast shade and help keep us cool, reduse our
cooling bills, and provide a pleasant "ceiling" for our landscape.  Unless
they are impinging on a power line, consider leaving the large trees alone.
Trees do not, for their own health, ever need pruned if they are properly
cared for.  Prune only to remove dead, damaged, or diseased limbs, and never
prune at the height of Summer.  You might prune slowly, over time, if you
need to "lift" the canopy to walk under it, but that's really about it.
You've seen the results of severe pruning, and unfortunately that damage s
permanent, but you can avoid similar damage in the future.  

I hope this helps,
Tyler

tyler at tylerstorey.com
http://tylerstorey.com
602-738-2978

-----Original Message-----
From: veronicaavarela at cox.net
Sent: Wednesday, September 12, 2007 6:05 AM
To: arid_gardener at Ag.arizona.edu
Subject: [Arid_gardener] Question from Home-Hort WWW page

veronica
85226
veronicaavarela at cox.net

We live in Chandler and about two months ago had 2 well established palo
verde trees pruned as they were huge.  The pruning was severe but the trees
bounced back and actually are once again in need of trimming .  Problem...we
have noticed striations on trunk and brances...splits and holes that are
highly visible as they look like dry,brown streaks, patches and holes. They
increase daily and now cover most of the trunk as well as major branches.
What is it and can it be treated?  These trees are very beautiful and really
enhance our front landscaping....


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