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This website is dedicated to Bert Wilson. His genius continues to inspire us.

California Oaks II

Valley oak, Blue oak and Engelmann oak are the common oaks of the inner valleys in California.

Acorn matures in one season (at end of new stems)

Acorn matures in two seasons (on older stems)

I. Evergreen

Quercus agrifolia, Q. x alvordiana, Q.dumosa, Q. durata, Q. sadleriana, Q. turbinella

II. Deciduous

Quercus garryana var. breweri, Q. douglasii, Q.engelmannii, Q. garryana, Q. lobata


Quercus chrysolepis, Q. parvula, Q. tomentella, Q. vaccinifolia, Q. wislizenii, Lithocarpus densiflorus (Tanbark Oak)

IV Deciduous

Q. kelloggii, Q. palmeri

How to take care of your oak trees.

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Oak relationship chart

II. California Oaks that bear acorns on each season's growth and are deciduous.

Blue Oak – Quercus douglasii- The Blue Oak lives from about Los Olivos in the coast ranges and Lebec in the interior and north through the coast ranges and the west base of the Sierra Nevada mountains to around Lake Shasta. This is a very drought tolerant tree; in much of its normal range the rainfall is an irregular 7-10 inches each year (same as much of the Mojave Desert). Blue Oak has bluish-tinged leaves, and the leaves are deciduous and sometimes prickly. This oak grows very slowly. We have seen some pretty large ones, however. Blue Oak is commonly a round headed, 20-30 ft. tree.
Blue Oak - Quercus douglasii goes deciduous - grid24_6
The blue green leaves can be fuzzy, slightly rolled, flat, smooth, entire, slight lobed, have small bristles or none.

Where hybrids with Valley Oak (Quercus lobata) occur (Quercus douglasii X Q. lobata or Quercus x jolonensis) you can find some huge 'Blue Oaks' that are really stable (and fertile) hybrids. There are some of the giant hybrids in west Atascadero, around Jolon, and a whole valley of them east of Pozo.

You can also find hybrids with Oregon Oak (Quercus garryana) in Blue Oak's northern range. This hybrid has been called Q. x eplingii

Blue oaks (Quercus douglasii) hybridize with many of the other oaks in California and often you're left guessing which it is. Sometimes Blue Oaks (Quercus douglasii) and Valley Oaks (Quercus lobata) get together and you get more hybrids than 'real' trees. Sometimes Blue Oaks (Q. douglasii) and scrub oaks (Quercus berberidifolia) make a mess of little oaks that leave most of us confused and one or two newbie botanists thinking up new species names.
I would be very happy if a group of botanists by consensus combined almost all the oaks into one species, with the subspecies, forms, varieties and hybrids listed under them. THEN, if you were not sure which one you were looking at you could 'go up the tree' one step.

We have hillsides where Coast Live Oak (Quercus agrifolia), Valley Oak (Quercus lobata), Tucker's Oak (Q. john-tuckeri) , Blue Oak (Q. douglasii), Nuttall's Scrub Oak (Q. dumosa) , hybrids (Q. dumosa X Q. lobata, Q. dumosa X Q. douglasii, Q. john-tuckeri X Q. douglasii, and sometimes what appear to be evergreen Blue Oaks all together in an area the size of a football field. The blend and morph into each other . Almost every tree leaves you scratching your head. They cannot all be different named species, not with all the “kids” around that do not fit.

Blue Oak

Engelmann Oak, Quercus engelmannii is deciduous, or evergreen, depending upon environmental conditions, with lobed leaves with a bluish tinge, not prickly, a smaller round form, and very drought tolerant. This oak ranged from Pasadena to Baja usually away from the coast, but not in the desert or higher elevations. It's a flat lander, foothill or valley dweller. Not many are found as you hike through the chaparral or pine forests. It is commonly associated with the shallow rocky soils that can't support much more than bulbs, grasses, sages, buckwheats and forbs, and then Engelmann Oaks Quercus engelmannii), Ribes spp., Rhamnus spp., and sometimes Rhus spp. make a colony in a patch of deeper soil.
Oregon Oak- Quercus garryana is not so drought tolerant,and grows more in the northern part of the state from about Santa Cruz north and across into the Siskiyou mountains and down into the Northern Sierra Nevada mountains.
Quercus garryana breweri, Brewer's Oak - grid24_12
Quercus garryana var. breweri is the scrub form of Oregon Oak called Shin Oak. It grows from the lower Sierra Nevada mountains north and along the coast ranges from about Santa Cruz northward.
Valley Oak, Quercus lobata is a large deciduous tree. The biggest Valley Oaks  I've heard about were in Shandon and Ojai, both were about 150 ft. tall. (Or so the stories go.) Valley oaks used to be in most ofthe seasonally flooded areas of the San Joaquin Valley. The area around Hanford and Riverdale were described as park like with huge Valley oaks and Alkali Rye and Grape under them.

A short video about Valley Oak.

Different hybrids (other than the Blue Oak hybrids listed above)
Quercus x kinselae and Quercus x macdonaldii are hybrids of Q. lobata and Q. dumosa
Then there's a hybrid of Q. lobata with Q. john-tuckerii (Quercus lobata var. insperata)
Q. x munzii (Q. lobata X Q. turbinella)
Q. x townei (Q. dumosa X Q. lobata)
Quercus lobata has also been known to hybridize with Q. garryana and Q. kellogii (see our Q. kelloggii)