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Quercus douglasii

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About Blue Oak (Quercus douglasii) The Blue Oak is endemic to California and is found in foothills surrounding the Central Valley of California, the South Coast Range, North Coast Range and San Francisco Bay Area. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak. Blue Oaks are medium-sized deciduous trees growing up to 50-82 feet tall, usually with a somewhat irregularly-shaped crown, and a trunk 1.5-3 feet in diameter. The tallest recorded oak was found in southern Alameda County, at 94 feet The bark is light gray with many medium-sized dark cracks; from a distance, it can appear almost white. The name Blue Oak derives from the dark blue-green tint of its leaves, which are deciduous, 1.5-4 inches long, and entire or shallowly lobed. The blue color can be subtle but becomes much more evident when viewed next to one of the live oaks with whom it shares its range, which tend to have much greener leaves. The acorns are around an inch long, often with a narrowed base, with a moderately sweet kernel, and mature in 6-7 months from pollination.

Blue Oaks are beautiful but very slow growing trees. They usually only add a few inches per year. Plant on dry, well drained slopes. They prefer full sun but will tolerate part shade, especially when young. They can handle occasional summer water (1x per month).
Plant Description
Plant Type

Max. Height
16 - 82 ft (4.9 - 25 m)

Max. Width
30 ft (9.1 m)

Upright, Rounded, Upright Columnar


Growth Rate

Summer Semi-Deciduous, Winter Deciduous

Flower Color
Yellow, Cream, Green

Flowering Season
Spring, Winter

Native Status

Natural Setting
Site Type
Rocky, hot, dry hillsides and slopes usually below 3,500 ft. in the Coast Ranges and foothills of the Sierras, often in large stands of Blue Oak Woodland or Blue Oak Savannah

Sun, Part Shade

Elevation ?
6' - 11310'

Annual Precip. ?
7.8" - 71.1"

Summer Precip. ?
0.14" - 2.08"

Coldest Month ?
24.6° F - 56.2° F

Hottest Month ?
45.5° F - 80.0° F

Humidity ?
0.53 vpd - 27.98 vpd

Soil Description
Tolerant of a variety of soils as long as adequate drainage is provided

Soil PH
6.0 - 8.0


Cold Tolerance(° F)
Tolerates cold to 0° F

Sunset Zones ?
1, 2, 3, 4, 5, 6, 7*, 8, 9*, 10, 11, 14*, 15*, 16*, 17, 18*, 19*, 20*, 21*, 22, 23, 24

Wildlife Attracted
A very large variety of wildlife are attracted to oaks. Many insects are attracted to Oaks generally, including the following butterflies which use Oaks as host plant: California Sister, Propertius Duskywing, Mournful Duskywing, Golden Hairstreak, and Gold-Hunter's Hairstreak.

Landscaping Information
Ease of Care
Very Easy

Water Requirement ?
Extremely Low
Very Low
Moderate - High

Moderately Popular

Max. Summer Water ?
No Summer Water
Keep moist

Organic with Rocks

Young trees should be pruned for desired shape

Propagation ?
From acorns, although hybridization is common.  For propagating by seed: Fresh seeds sow in fall outdoors or stratify to hold for spring sowing. If started indoors or in glasshouse, stratify first for 1.5 mos. (USDA Forest Service 1974).

Common uses
Bank Stabilization, Deer Resistant, Bird Gardens, Butterfly Gardens

Nursery Availability
Commonly Available

Other Names
Common Names
Occasionally Iron Oak, Mountain Oak

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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