Tree Blog

Quercus oblongifolia | Coastal Southern California

Here we see the characteristic blue-green color of Mexican Blue Oak (Q. oblongifolia) on a boxed nursery tree. The foliage is very similar to that found on the examples cited earlier from the Los Angeles Country Arboretum. The lush growth seen here, with even more new growth just beginning to expand, shows that Mexican Blue Oak can thrive under typical nursery conditions. Growing Mexican Blue Oak in rural Ventura County has shown the trees to have limited susceptibility to powdery mildew. Even this small level of powdery mildew is further reduced when looking at the closely related Engelman Oak, (Q.engelmannii). Engelman Oaks recent evolutionary history in coastal southern California has likely enhanced its resistance to powdery mildew. This enhanced resistance suggests that something about the change to greener pigementation has proved protective against powdery mildew. This further suggests that, if a choice is to be made between planting Engelman Oak and Mexican Blue Oak, Engelman should perhaps be favored in coastal locations, while Mexican Blue Oak is best utilized in persistently low humidity inland locations.

Dave Muffly