Blue Oak

Quercus douglasii


This California oak is native to our area, usually growing on dry or rocky hills. Its blue-ish leaves, wide-spreading shape, and picturesque branches make it easy to spot in open space preserves. It grows slowly, is very drought tolerant and tough, and lives a long time – several hundred years is not uncommon. The leaves take on a distinctly blue-green tinge in summer and the bark has patchy light-colored areas. When mature, Blue Oaks produce large acorns.


The blue-green leaves of this tree reflect the sun, conserving water for the 5 to 7 months of the dry season. The Blue Oak cannot handle frequent summer watering or lawn around its roots. Our soils have a fungus that is kept in check by dry summers, but wet soil in the summer invigorates the fungus and allows it to attack the tree and weaken or kill it. Keep your Blue Oak healthy by watering infrequently during the summer and putting a thick layer of mulch under the canopy to keep the soil cool.

Blue Oak

Height: 30 to 50 feet
Spread: 40 to 70 feet
Growth Rate: slow to moderate

Irrigation needed: very low water
Fall Color: none
Flowers:  inconspicuous catkins
Seeds/Fruit: acorns

Planting Distances
Front of green utility box: 8 feet
Building, paving, swimming pool: 20 feet
Fence, underground utilities: 6 feet
Overhead, high voltage lines: 30 feet