Douglas Fir (Pseudotsuga menziesii)

The Common douglas-fir is named after Scottish botanist David Douglas, who discovered it. Small mammals rely heavily on the seeds for nutrition. Many Native American tribes utilized the bark, resin, and pine needles to prepare herbal remedies for various ailments. Common douglas-fir is often used in heavy timber buildings due to its sturdy wood.

I. Appearance and Characteristics

The Douglas fir (Pseudotsuga menziesii) is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three varieties: coast Douglas-fir (P. menziesii var. menziesii), Rocky Mountain Douglas-fir (P. menziesii var. glauca) and Mexican Douglas-fir (P. menziesii var. lindleyana).

Despite its common names, it is not a true fir (genus Abies), spruce (genus Picea), or pine (genus Pinus). It is also not a hemlock; the genus name Pseudotsuga means “false hemlock”.

Douglas-firs are medium-size to extremely large evergreen trees, 20–100 metres (70–330 feet) tall (although only Pseudotsuga menziesii var. menziesii, common name coast Douglas-firs, reach heights near 100 m) and commonly reach 2.4 m (8 ft) in diameter, although trees with diameters of almost 5 metres (16 feet) exist. The largest coast Douglas-firs regularly live over 500 years, with the oldest specimens living for over 1,300 years. Rocky Mountain Douglas-firs, found further to the east, are less long-lived, usually not exceeding 400 years in age.

There are records of former coast Douglas-firs exceeding 120 metres (390 feet) in height, which if alive today would make it the tallest tree species on Earth. Particular historical specimens with heights exceeding 400 feet include the Lynn Valley Tree and the Nooksack Giant.

The leaves are flat, soft, linear needles 2–4 centimetres (3⁄4–1+1⁄2 in) long, generally resembling those of the firs, occurring singly rather than in fascicles; they completely encircle the branches, which can be useful in recognizing the species. As the trees grow taller in denser forest, they lose their lower branches, such that the foliage may start as high as 34 m (110 ft) off the ground. Douglas-firs in environments with more light may have branches much closer to the ground.

The bark on young trees is thin, smooth, grey, and contains numerous resin blisters. On mature trees, usually exceeding 80 years, it is very thick and corky, growing up to 36 cm (14 in) thick with distinctive, deep vertical fissures caused by the gradual expansion of the growing tree. Some of the mature bark is brown, while other parts are lighter colored with a cork-like texture; these develop in multiple layers. This thick bark makes the Douglas-fir perhaps the most fire-resistant tree native to the Pacific Northwest.

The female cones are pendulous, with persistent scales, unlike those of true firs. They have distinctive long, trifid (three-pointed) bracts which protrude prominently above each scale and are said to resemble the back half of a mouse, with two feet and a tail.

The massive mega-genome of Douglas fir was sequenced in 2017 by the large PineRefSeq consortium, revealing a specialized photosynthetic apparatus in the light-harvesting complex of genes.

II. How to Grow and Care

Sunlight

Common douglas-fir thrives best under full sun conditions, receiving unfiltered sunlight for at least 6 hours a day. It possesses high adaptability, tolerating partial sun with some light shade, though this might slightly compromise its growth vigor and density. Adapting to varying light levels, common douglas-fir can show adjustments in foliage density and orientation to maximize light absorption.

When grown outdoors, common douglas-fir should be placed in a location with clear exposure to the sky, ideally away from taller structures or trees that could significantly block sunlight. Its robust nature accommodates a range of outdoor environments, but optimal light availability is crucial for its health and growth.

Temperature and Humidity

Douglas fir, scientifically referred to as Pseudotsuga menziesii, is a sturdy evergreen tree that adapts well to a variety of climates, ranging from the arid regions of Mexico and Arizona to the cold, rocky mountains.

Its natural habitat extends from central British Columbia along the Pacific coast to central California, highlighting its resilience to diverse weather conditions. However, it thrives best in the moist conditions of the Pacific coast and is resilient to drought once established.

The Douglas fir prefers cooler climates and can withstand temperatures well below freezing. Regardless of temperature, maintaining adequate humidity is crucial, especially during the dry summers when the soil is most prone to drying out.

Watering

Originating from moist forest environments, common douglas-fir has adapted to thrive with moderate moisture levels. This species exhibits a preference for consistent humidity and is moderately drought-tolerant. Watering practices should mimic its natural habitat, equating to once every 1-2 weeks. Typically found outdoors, common douglas-fir benefits from the seasonal rainfall patterns that align with its growth cycles, ensuring optimal hydration during key developmental phases.

Soil

The Douglas Fir, known scientifically as Pseudotsuga menziesii, is a versatile and hearty evergreen tree that has the capacity to grow in a wide range of soil types.

However, it thrives best in well-draining, moist soil. It can also adapt to drier soil conditions, proving its ability to withstand drought.

Regardless of location, whether in the Rocky Mountains, Arizona or Central California, the preference for full sun remains constant for this remarkable tree.

Fertilizing

To foster robust growth in common douglas-fir, apply a balanced nutrition fertilizer annually, ideally in early spring before new growth starts. Benefits include improved health and vigor. Use fertilizer according to its label, avoiding over-fertilization which can harm common douglas-fir. During the active growing season, lighter, more frequent feedings may be beneficial. Always water common douglas-fir thoroughly after fertilizing to facilitate nutrient uptake. For young common douglas-fir, more nitrogen-rich mixes support growth, switching to phosphorus and potassium as common douglas-fir matures to encourage root and shoot development.

Pruning

Usually, pruning should be carried out when the tree is dormant, removing only dead, diseased, or broken limbs. Care should be taken not to damage the main trunk and always remember to prune where the branch collar ends.

If you are pruning for density, do it moderately in the full sun locations to avoid drought stress. Leave enough needles to photosynthesize sufficiently, while opening up the grain of the tree to sufficient light and air circulation to keep it healthy.

Propagation

The ideal propagation season for common douglas-fir is during Autumn and Winter, with preferred methods being layering, cutting, and sowing. Propagation is moderately difficult, but successful indicators include root development and new growth. Ensure proper soil preparation and moisture for optimal results.

Transplanting

The ideal season to transplant common douglas-fir is from mid-spring to late spring or mid-winter to late winter, allowing roots to establish before seasonal growth. Ensure the transplant location has well-drained soil and partial to full sunlight. Gently tease the root ball when transplanting, if needed, to encourage healthy growth.

Pests and Diseases

Common Pests and

Diseases

• Douglas-fir Beetle

The Douglas-fir Beetle is a common pest of the Douglas fir. These pests, which are attracted to the tree’s light brown bark and needles, bore into the tree, feed off its grain, and lay eggs on the inner bark. In extreme cases, they can lead to the decline and death of these venerable pines.

• Swiss Needle Cast

Swiss Needle Cast is a plant disease that is particularly problematic for Douglas firs, often identified by yellowing and premature needle loss on lower branches.

The disease thrives in moist soil and shaded environments, making the Pacific Coast a perfect breeding ground, fulfilling its requirements of full sun and moist soil. If left untreated, the disease can hinder growth and potentially lead to the death of the young tree.

• Bark Beetles

Bark beetles can inflict serious damage on Douglas firs, creating networks of tunnels beneath the bark and potentially killing a young tree. Regular monitoring of the bark and the application of appropriate insecticides can protect your trees.

• Root Rot

Root Rot, caused by fungi, manifests as a sudden wilt and dieback of Douglas firs. It prefers areas with poorly drained soil, which allows the fungus to grow and thrive.

Once infected, the fungus obstructs the tree’s ability to absorb water and nutrients, leading to tree decline and potential death under drought conditions.

• Spruce Budworm

The Spruce Budworm, despite its name, does not only target spruces but can also cause significant damage to Douglas firs. This pest feeds on the young needles and cones, leading to a reduction in annual growth and weakening the tree.

Given enough time and severe infestations, it may eventually cause the death of Douglas firs, one of the tallest and most abundant evergreen trees in the United States.

• Armillaria Root Disease

Armillaria Root Disease is a common disease affecting the Douglas fir. Its effects can be seen primarily on lower branches, where there is a significant reduction of leaves, indicating the tree’s deteriorating health. This disease can be lethal and spells disaster mainly for Douglas firs found in central California.

Common Problems

• Yellowing Leaves

Yellowing leaves often suggest a nutrient deficiency within your Douglas fir. Affected Douglas fir trees, commonly known in Canada as the Oregon pine, need a nutrient boost. You can supplement the soil with all-purpose garden fertilizer to relieve the yellowing.

• Drought Stress

Despite Douglas fir trees being large, evergreen trees that can withstand various environments, they can still suffer drought stress. Symptoms include dropping lower branches and needles turning a light brown color.

Regular watering during dry seasons can help these Western North America natives handle drought better.

• Cones Dropping Early

Douglas fir trees are known for their unique cones featuring reflexed bracts, a trait uncommon to true firs of the Abies genus.

However, if cones are dropping prematurely, the tree might not be receiving enough water. Regular watering in dry conditions can help ensure healthy growth.

III. Uses and Benefits

Many different Native American groups used the bark, resin, and needles to make herbal treatments for various diseases. Native Hawaiians built waʻa kaulua (double-hulled canoes) from coast Douglas-fir logs that had drifted ashore. The wood has historically been favored as firewood, especially from the coastal variety. In addition early settlers used Douglas fir for all forms of building construction, including floors, beams, and fine carving. Even today much of the Northwest chain saw art is completed on Douglas fir logs. The structures built from fir have lasted 150 years and more.

The species is extensively used in forestry management as a plantation tree for softwood timber. Douglas-fir is one of the world’s best timber-producing species and yields more timber than any other species in North America, making the forestlands of western Oregon, Washington, and British Columbia the most productive on the continent.

In 2011, Douglas-fir represented 34.2% of US lumber exports, to a total of 1.053 billion board-feet. Douglas fir timber is used for timber frame construction and timber trusses using traditional joinery, veneer, and flooring due to its strength, hardness and durability. As of 2012, the only wooden ships still currently in use by the U.S. Navy are Avenger-class minesweepers, made of Douglas-fir.

Douglas fir sees wide use in heavy timber structures, as its wood is strong, available in a number of specifications including kiln dried and grade stamped, and can be supplied in very long lengths to 60 feet. West coast mills are sophisticated in their processing of timbers, making lead times predictable and availability reliable.

Paints adhere well to Douglas fir. Stains perform well on Douglas fir timbers with the mild caution that the natural color of this species varies and care must be taken to ensure uniformity of color. Pitch pockets that may ooze resin can be present in timbers that have not been kiln dried. Because of the timber sizes available, stamped timber grading, and relatively short lead times, Douglas fir sees wide use in both public and residential projects.

The species has ornamental value in large parks and gardens. It has been commonly used as a Christmas tree since the 1920s, and the trees are typically grown on plantations.

The buds have been used to flavor eau de vie, a clear, colorless fruit brandy. Douglas-fir pine leaves can be used to make pine needle tea. They possess a tangy citrus flavor and may serve in some recipes as a wild substitute for rosemary.