Q. douglasii - Blue Oak

The blue oak - Tree identifier

A large California native that is not prone to Sudden Oak Death ( however there are conflicting reports saying it is prone though less than Tanoak and other "Red Oaks" )

. It is very drought tolerant growing without irrigation once established in regions with 12 to 32 inches of rainfall per year and with soil PH from 4.5 to 7.5. On ideal sites this Oak grows large with a rounded crown to 80 feet and the largest records is 120 x 50 feet with a trunk diameter of 7 feet. One huge tree grows in s. Alemeda County in California.

Both very drought tolerant and long lived ( up to 500 years ); this Oak makes an excellent urban street tree in the West. It should be planted more especially because unfortunately destruction of its natural habitat has made it endangered in the wild.

The oblong foliage is deciduous and up to 5 x 2 inches in size. The leaves have either smooth margins or 4 to 5 somewhat shallow lobes. They are blue-green in summer and turn an unusual pinkish color in the fall. It is the waxy coating that gives the leaves its bluish cast that also blocks evaporation and helps these trees withstand the long dry summers of Californias Mediterranean climate.

Also with Oaks of the southwest U.S.; vessels that conduct water in stems and roots much be able to withstand unusually great internal tensions

As summer drought progresses, newly formed oak vessels become progressively thicker, harder and more compact, decreasing the likelihood of collapse as

roots withdraw the last droplets of soil-bound moisture.

If water finally becomes too scarce, blue oaks simply drop their leaves, a condition

known as drought deciduous. They will then leaf out the following spring after soaking up winter rains.

Unlike most Red Oaks; the acorns of this tree are tasty and sweet and mature in one season.

The bark is gray-brown and scaly. Hardy north to zone 6 though there are unverified reports of 5. It is not known to grow in humid summer climates of the eastern U.S. and as far as I know I'm not even sure it has been tried.

האלון הכחול מסתגל לקיץ יבש - (אנגלית)