The number 1 toughest native tree locally would have to be, in my experience as an arborist, is the mighty Oregon white oak, Quercus garryana. The abuse heaped on these wonderful oaks is voluminous! Old East Medford has many examples of this, and I am shocked to see conditions that would outright kill any other oak, barely faze a mature Garry oak…
From raising the grade of the soil, to installation of turfgrass, constant summer irrigation and the like, the Oregon white oak can tolerate a HUGE amount of abuse!
What kills all oaks eventually is usually decay coupled with a sudden gust of gravity, but Oregon white oaks are fortunately pretty damn hard to kill.
Various pathogenic fungi that commonly exist in our soils seem to have some difficulty in infecting them to the point of causing total tree failure.
If you raise the natural soil grade on top of say a California black oak’s root zone and install a lawn, you have pretty much signed its death warrant.
It also should be said that if you do this to an Oregon white oak, it may not be the fastest way to kill it, but may be the surest way to cause its decline and eventual death.
It may just be that Oregon white oaks just grow soooo slow that it just takes longer! At this time of year it is easy to see the infections of leafy mistletoe in the canopies of the Garry oaks everywhere. This scourge of the oak can and will kill them if given the chance, and the drain on the trees vascular system can set the stage for plethora of other organisms that hasten the eventual death of your beloved Garry oak. Frequent summer irrigation paves the way for pit scale infestation, oak root fungus, and other nasties and If you just MUST have a lush green lawn up to the stem of your oak, it comes with a hefty price…
You should expect a fairly long interval between visits from your arborist if you follow some basic guidelines. Number one, keep in mind that Oregon white oaks have evolved, locally anyway, in a relatively dry climate. Not that they don’t need moisture mind you, but a water cannon blasting the stem is a no-go.
To me an Oregon white oak reminds me of something between a Valley oak and a Blue oak but way tougher than either or both.
The best thing you could possibly do for your Oregon white oak is simply, let it be itself!
Don’t change the soil grade within the root zone.
Forget about the lawn idea.
Keep frequent summer irrigation to a bare minimum.
Never, and I mean NEVER, over prune or “top” your oak!
Consult an arborist BEFORE you plan to make changes to the native environment within the living quarters of your beloved Garry oak. Pruning of large dead branches and the removal of the vegetative portion of leafy mistletoe every few years goes a long way to making your Garry oak a happy camper.
The better you treat your tree, the longer the interval between arborists invoices you will incur! That said, acorns are pretty much free,
so…
As always, plant high and often.
