Douglas-fir

Pseudotsuga menziesii (Pinaceae) is a massive evergreen conifer native to western North America from British Columbia to central California and through the Rocky Mountains to Arizona and Texas. The coastal form is the taller, reaching 200 feet or more, while the interior (Rocky Mountain) form is smaller and more cold-hardy. Flat, spirally arranged dark green needles are fragrant when crushed. The distinctive cones have three-pronged bracts protruding beyond the scales, making identification easy.

Douglas-fir grows in sun to part shade on a range of well-drained soils (pH 5.0 to 7.5). It is the most commercially important timber species in North America and the state tree of Oregon. Growth rate is moderate to fast depending on site quality. The coastal form can live 500 years or more. Numerous cultivars exist, including 'Pendula' (weeping) and dwarf forms. Disease and pest pressure is significant, with 14 diseases and 18 pests documented. Hardy in Zones 3b to 8b.

Provenance matters more than anything else with Douglas-fir. Coastal seed sources (var. menziesii) handle our wet winters and resist needle casts that devastate Rocky Mountain stock planted west of the Cascade crest. If you are planting Doug-fir and the nursery cannot tell you the seed source, walk away. In the Puget Sound lowlands this tree grows fast on deep, well-drained loam and tolerates our summer drought once established, but it does not belong in waterlogged valley bottoms or over shallow hardpan where water perches. The diseases that matter here are Rhabdocline needle cast and Swiss needle cast; both thrive in our cool, wet springs. Tussock moth and spruce spider mite flare in dry summers. Mature specimens need virtually no maintenance, but newly planted trees benefit from summer irrigation through year three.

— Chris Welch, ISA Certified Arborist