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Though there is more than one native Quercus to our region (Q. kelloggii, California black oak and Q. brewerii, Brewer's oak, both of which only venture up into southern Oregon), the only one that is commonly found here is Q. garryana, the Oregon white oak or Garry oak which, when given full room to spread its lush branches, becomes the epitome of the "mighty oak" of literature: In the vast open spaces of the fertile Willamette Valley for example, it can eventually command a space seventy-five feet tall and sixty feet wide (It's that huge, elegant tree you see standing alone in the field as you drive down the back roads of the Valley). But never fear, in most garden sites it holds itself to much less gargantuan stature, and is very slow-growing, besides, reaching only about twenty-five feet in twenty years.
Though you need a bit of space to house an Oregon oak, it is worth the space if you have it. Laden with the recognizable lobed, classic oak leaves of deep dark green, it produces an abundance of small acorns in summer and fall that are a favorite of many species of birds, making it an excellent choice for a wildlife-attracting garden. The flowers are of little notice, but the fall foliage is yellow to coppery-orange/brown, and provides an attractive contrast to the fissured gray of the trunk. A deciduous tree with intricate branching, it also provides a sculptural element in winter.
The important thing about including an Oregon oak in your landscape is to site it where it can have mostly full sun, excellent drainage and especially no summer water; some fungus problems and lack of vigor with this plant can often be traced to retained moisture in the soil.
Numerous insects make use of the native Quercus, most of which do little or no damage except sometimes to the acorns, which will not be a bother unless you are trying to use them for food or commercially (and may indeed provide food source for visiting birds). The tiny gall wasp (Cynips maculipennis) is responsible for the small galls that sometimes appear on the underside of the tree's leaves, but they do not seem to negatively impact the health of the tree itself. There are also certain moth larvae for which the oak is the only food source. So the native Quercus is truly a full-spectrum habitat plant!
There are many native shrubs and perennials that grow companionably with Q. garryana, so you can very successfully use it as the anchor for a more extensive native plant garden, and enjoy it throughout the year and for many, many years.
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Common name: Garry oak, Oregon white oak
Native Range: From British Columbia south through northern California, primarily along the temperate corridor that includes Puget Sound and the Willamette Valley.
Characteristics: Majestic tree with spreading canopy of dark green, classically-oak-lobed leaves about three inches in diameter. Bark is an attractive fissured gray. Produces an abundance of reddish brown acorns, which are a favorite with many species of birds. Deciduous leaves turn yellow-brown in fall. Grows very large and densely in fertile soils, smaller and more contorted in poorer, rockier conditions. Tends to stay shrubbier in typical garden settings.
Culture: Oregon oak is found growing everywhere from seasonally wet meadows to dry, rocky outcrops; but in the wetter locations still receives dry summer conditions. Plant in a sunny location with good drainage, where it won't get summer water
Pests/Diseases: Can be afflicted with fungal diseases; planting in location with adequate drainage and lack of summer water can go a long way in protecting your tree from fungal damage. Also can attract gall wasps that produce small galls on the undersides of leaves. These, however, don't appear to cause any damage to the plant. More good news: Q. garryana has not been shown to be affected by the disease causing what is commonly called Sudden Oak Death.