Pictured above are a few Acacia Salicina, AKA "Willow Acacia". I took these particular pictures in Gilbert, but it is not unusual to see them used throughout newer (1-20 years old) developments in Mesa, Chandler, Scottsdale, and others, both residential and commercial. Very often, I would say 1/3, or more, they look like the ones above. For some reason they are used as parking lot and street trees a lot. I just don't get it.
OK, so before I go on breaking down just how bad of a choice planting these trees in Arizona Landscapes can be -especially in above mentioned situations- let me say that every tree has it's place and I am not knocking the tree, the way in which it is used. The trees don't choose where and by whom they are planted !
Cons to Acacia Salicina for city use:
1. Require a lot of trimming/maintenance (which also means lots of man-power, dump trips, etc)
2. Branches are quite likely to break in the wind because of rapid, erratic growth
3. VERY shallow (and invasive) root system (you can see the surface root top left, just waiting for a combination of rain and wind - hmmm... Arizona Monsoons? This is one of the most common trees you see blown over during "micro bursts" or even moderate storms)
4. Inconsistent growth rates, inconsistent structures in general. Not a plus for a city street tree or providing shade.
5. Consistently produce pollen, pods, cycle through leaves, creating a need for more maintenance, clean-up, gas blowers, dump trips, etc. (mess level - 8.5/10)
So after all this hard work, keeping it in line, cleaning up, dealing with emergency service bills ($) for broken branches and fallen trees, here is the toughest part to swallow.......drum roll......
A lot of these trees, after all the investment our tax dollars (or personal dollars) and the energy of the maintenance crews put in..... A very large amount of them will have to be replaced, thus requiring costs of removal -labor, hauling, dump again, costs of buying a new tree, labor to plant it. And finally our city's or our neighborhood's maturity and character (which is SO essential, especially in the rapidly growing, culture struggling to keep up Valley we live in) starts all over after all this work ! And it's quite possible the replacement could be another Salicina !
Now I am feeling bad for harping on the tree. It didn't decide to come from Australia to Arizona. Somebody realized they were easy to grow, fast growing, and inexpensive. ($$) This is similar to what seems to have been a Eucalyptus craze in the eighties. And the more current Sissoo over-use :)
I will end with some pro's: fast growing, beautiful weeping look, great for farms or riversides, especially in Australia :) See, isn't that better !
Adam Bruce
PS - I don't want to be cynical often in this blog, but this has been bothering me for about a decade. Please hire a professional to help you select trees and locations, it makes a big difference for all of our futures.
PSS - Another culprit with strikingly similar issues is the Chilean Mesquite (there are many types of Mesquites that grow well here and are reliable, it's just this particular one and it's over-use that is many times a true waste of resources)
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