Pseudotsuga menziesii var. glauca: Rocky Mountain Douglas-Fir1
Douglas-Fir grows 40 to 60 feet and spreads 15 to 25 feet in an erect pyramid in the landscape. The species grows to more than 200 feet tall in its native habitat, but this variety grows slower and is smaller than the species and has very attractive blue-green foliage. Hardiness varies with seed source, so be sure it was collected from an area with suitable cold-hardiness to the area in which it will be used.
Scientific name: Pseudotsuga menziesii var. glauca
Pronunciation: soo-doe-SOO-gah men-ZEE-zee-eye variety GLAW-kuh
Common name(s): Rocky Mountain Douglas-Fir, Blue Douglas-Fir
USDA hardiness zones: 5A through 6B (Fig. 2)
Origin: native to North America
Invasive potential: little invasive potential
Uses: screen; specimen; Christmas tree
Availability: not native to North America
Height: 40 to 60 feet
Spread: 15 to 25 feet
Crown uniformity: symmetrical
Crown shape: pyramidal
Crown density: moderate
Growth rate: moderate
Leaf arrangement: alternate (Fig. 3)
Leaf type: simple
Leaf margin: entire
Leaf shape: needle-like (filiform)
Leaf venation: parallel, none, or difficult to see
Leaf type and persistence: evergreen, needled evergreen
Leaf blade length: less than 2 inches
Leaf color: blue or blue-green
Fall color: no color change
Fall characteristic: not showy
Flower color: red
Flower characteristics: not showy
Fruit shape: oval, cone
Fruit length: 1 to 3 inches
Fruit covering: dry or hard
Fruit color: brown
Fruit characteristics: does not attract wildlife; showy; fruit/leaves not a litter problem
Trunk and Branches
Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns
Pruning requirement: little required
Breakage: susceptible to breakage
Current year twig color: green
Current year twig thickness: thin, medium
Wood specific gravity: unknown
Light requirement: full sun
Soil tolerances: clay; sand; loam; acidic; well-drained
Drought tolerance: moderate
Aerosol salt tolerance: unknown
Roots: not a problem
Winter interest: yes
Outstanding tree: no
Ozone sensitivity: unknown
Verticillium wilt susceptibility: resistant
Pest resistance: resistant to pests/diseases
Use and Management
Douglas-Fir is most commonly used as a screen or occasionally a specimen in the landscape. Not suited for a small residential landscape, it is often a fixture in a commercial setting. Allow room for the spread of the tree since the tree looks terrible with lower limbs removed. Grown and shipped as a Christmas tree in many parts of the country.
The tree prefers a sunny location with a moist soil and is not considered a good tree for much of the South. It grows but struggles in USDA hardiness zone 7. Douglas-Fir transplants best when balled and burlapped and has a moderate growth rate. It tolerates pruning and shearing but will not tolerate dry soil for extended periods. Protect from direct wind exposure for best appearance. Some occasional watering in summer dry spells will help the tree stay vigorous, especially in the southern end of its range.
Cultivars of the species include: `Anguina' - long, snake-like branches; `Brevifolia' - short leaves; `Compacta' - compact, conical growth; `Fastigiata' - dense, pyramidal; `Fretsii' - dense bush, short broad leaves; `Glauca' - bluish foliage; `Nana' - dwarf; `Pendula' - long, drooping branchlets; `Revoluta' - curled leaves; `Stairii' - variegated leaves.
Aphids infestations on small trees may be dislodged with a strong stream of water from the garden hose.
Scale and bark beetles may infest Douglas-Fir, especially those under stress.
Root rot can be a serious problem on clay and other wet soils.
Needles infected by leaf cast fungi in spring turn brown and fall off.
Several fungi cause canker diseases leading to branch dieback. Maintain tree health and prune out infected branches.