Introduction

At first glance, this plant would hardly be thought to be an oak. Creating a very formal, dense, round or oval shade, evergreen blue Japanese oak grows slowly to 25 to 40 feet in height with a spread of 25 to 35 feet. The new growth is often bronze- or purple-tinted, and develops into shiny, dark green, 2.5- to 5.5-inch-long by 1- to 2.5-inch-wide, leathery leaves. It is a very attractive tree suited for many uses.

General Information

Scientific name: Quercus glauca

Pronunciation: KWERK-us GLAW-kuh

Common name(s): Blue Japanese oak, ring-cupped oak

Family: Fagaceae

USDA hardiness zones: 8A through 9B (Fig. 2)

Origin: not native to North America

Invasive potential: little invasive potential

Uses: street without sidewalk; parking lot island 100-200 sq ft; shade; parking lot island > 200 sq ft; tree lawn 3-4 feet wide; tree lawn 4-6 feet wide; tree lawn > 6 ft wide; highway median

Availability: not native to North America

Description

Height: 25 to 40 feet

Spread: 25 to 35 feet

Crown uniformity: symmetrical

Crown shape: round, oval

Crown density: dense

Growth rate: slow

Texture: medium

Foliage

Leaf arrangement: alternate (Fig. 3)

Leaf type: simple

Leaf margin: serrate, dentate

Leaf shape: oblong, obovate, elliptic (oval)

Leaf venation: pinnate

Leaf type and persistence: broadleaf evergreen, evergreen

Leaf blade length: 2 to 4 inches, 4 to 8 inches

Leaf color: green

Fall color: no color change

Fall characteristic: not showy

Flower

Flower color: brown

Flower characteristics: not showy

Fruit

Fruit shape: oval, round

Fruit length: .5 to 1 inch

Fruit covering: dry or hard

Fruit color: brown

Fruit characteristics: does not attract wildlife; not showy; fruit/leaves a litter problem

Trunk and Branches

Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns

Pruning requirement: needed for strong structure

Breakage: susceptible to breakage

Current year twig color: green, brown

Current year twig thickness: thick

Wood specific gravity: unknown

Culture

Light requirement: full sun

Soil tolerances: clay; sand; loam; acidic; occasionally wet; well-drained

Drought tolerance: high

Aerosol salt tolerance: unknown

Other

Roots: not a problem

Winter interest: no

Outstanding tree: no

Ozone sensitivity: unknown

Verticillium wilt susceptibility: resistant

Pest resistance: resistant to pests/diseases

Use and Management

Blue Japanese oak has been used as a street and parking lot tree in parts of the southeast for a number of years. Was used in USDA hardiness zone 7b until the 1983 freeze which reduced large trees to a collection of sprouts. It appears to be tolerant of drought and poor, clay soil including those which are poorly-drained and grows well in tight soil spaces. Its tight crown lends a formal feel to the landscape.

Many upright trunks and branches originate from one point on the trunk without initial training, and this structure could lead to a weak tree. Following initial training and pruning to develop a central leader and well-spaced branches, little care should be needed to maintain this tree. It should be grown and planted more in urban areas in the South.

Blue Japanese oak should be grown in full sun. It is tolerant of a wide range of soils, including heavy clay soils.

Propagation is by seed.

Pests and Diseases

There is a large number of potential problems on oaks, but none of major concern.