Pseudotsuga menziesii
Douglas fir is one of the most predominant trees found in forests of the PNW and western Canada. Native from B.C. south to northern Mexico. Valuable timber species, often found in landscapes as remnant of pre-development forest. Douglas fir can be distinguished from ‘true’ fir or spruce by the tassels, ‘beards’, or ‘mousetails’ on each cone scale.
- Culture
- Concerns
- Management
Culture for Douglas Fir
Performs best with moist, organic-rich, acidic soils. May develop multiple leads due to top-death from drought, storms, or lightning. Often topped in an attempt to reduce size and risk, but over time topped trees become more hazardous.
Concerns about Douglas Fir
Large branch failure in wind or with snow and ice loading. Armillaria root decay or Phaeolus schweinitzii (called ‘Schweinitzii root rot’) often lead to whole tree failure. Minor concerns with aphids, needle gall midge. Stressed trees often attacked by bark beetles.
Management Practices for Douglas Fir
If reducing wind resistance is desired, prune to shorten extended branches. Do not create ‘windows’ in canopy to reduce wind resistance, as this increases likelihood of large branch failure.
Inspect base of tree following early fall rains for mushrooms of Armillaria or conks of P. schweinitzii. Evidence of infection often appears as a flattened side of the trunk, or resinous oozing from the lower 5 feet of trunk. Oozing from higher up is usually an indication of overall stress, or is coming from pruning wounds.
Treat aphids and needle midge as warranted with systemic insecticide options.
Photos related to Douglas Fir
Pine cones
Top side of P. schweinitzii conk; bottom of conk will bruise purple
Yellow banding on needles is evidence of needle midge