Douglas Fir, Pseudotsuga: planting, pruning, and maintenance

Description and Botany

“`html

The genus Pseudotsuga comprises 4 species of very large Conifers, with records of 90 to 100 m tall and trunks up to 3 m in diameter. It includes three varieties, among which Pseudotsuga menziesii var. glauca, which grows only in the Rockies, featuring bluish foliage and lesser vigour, as well as a few dwarf cultivars (artificially obtained) intended for rockeries or pot cultivation. The Pseudotsuga are part of the Pinaceae family, like Pines, Firs, and Spruces. Two of its species, P. sinensis and japonica, come from the East (China, Japan, and Taiwan), while the other two, macrocarpa and menziesii, are found in the western part of North America, spanning from Canada to Mexico, from the Pacific coast to the Rockies.

The Pseudotsuga menziesii, which we will call Douglas, is the main species of Pseudotsuga cultivated, particularly as a timber species worldwide (Europe, Chile, New Zealand). Its wood is reddish-brown with cream nuances, hard, very durable and rich in resin, used for outdoor furniture or fencing but especially for frameworks, shipbuilding, or railway construction (after impregnation).

In its native range, Pseudotsuga menziesii occupies the Cascade Range and the western Sierra Nevada, often mixed with other giant resinous trees such as sequoias. It is almost naturalised in France, particularly in the Vosges, Jura, and Massif Central, where it sometimes reaches 60 m in height. This species is characterised by very rapid growth and ease of cultivation. The tree has a very straight cylindrical trunk with smooth grey bark and highly aromatic resinous vesicles. With age, it becomes spongy and fire-resistant, reaching up to 30 cm in thickness, and shows vertical reddish-brown cracks on a grey background that flake off at the surface. The habit remains pyramidal with horizontally raised branches at the tips that originate from the base of the trunk if not pruned, unlike other species that undergo natural pruning. The tree maintains a fairly narrow base that extends to a maximum of 8 to 10 m, while the species Pseudotsuga macrocarpa (“large-fruited”) sometimes found in collection gardens can spread 12 to 30 m wide for a height of 15 to 30 m.

The evergreen needles, dark green to bluish depending on the clone, are distributed on either side of the branch in a more or less opposite manner, often in a brush-like arrangement all around the branch in dwarf cultivars. They are narrow, flattened, flexible, and non-spiky, with a slight narrowing at the base and feature 2 light lines on the underside of the lamina. Their length varies from 2 to 4 cm with a width of 1 mm. Their friction releases a pleasant fruity scent that some describe as lemony, while others liken it to apple. Over time, their shedding leaves rough scars on the branch. The young shoots are pubescent. The buds of Pseudotsuga, tawny in colour, are very pointed, somewhat like those of beech, and are not resinous.

The Douglas Fir with its characteristic cones

Flowering occurs from late March to April with yellow male aments located beneath the shoots and female cones that are yellowish-green or pinkish at the tips of old shoots. Pollination occurs by wind.

The pendulous cones, 6 to 9 cm long, are easily identifiable by the trifid lobes protruding between the scales, corresponding to the bracts, which resemble snake tongues. The light brown cone scales are thin, similar to those of Spruces and Firs. As they open, they release brown seeds with wings, measuring 1.5 cm, between autumn and spring. Fruiting shows considerable fluctuations from year to year and begins relatively early, on trees aged 10 to 30 years.
“`

The main varieties of Pseudotsuga, Douglas

Most Popular Dwarf Varieties

Pseudotsuga menziesii Fletcheri - Douglas Fir

Majestic and flexible tabular bush with a broad habit, supported by tiered branches and very fine twigs. Its delicately textured foliage offers a very blue tint in spring. Perfect for large rockeries or small gardens. Hardy, for full sun, in light, well-drained, humus-bearing soil.

• Height at maturity 1,50 m

See the full description

Pseudotsuga menziesii Bhiela Lhota - Douglas Fir

Small rockery conifer that does not exceed 1 m after 20 years, with a very compact habit, initially globose, then pyramidal and wide, resembling a small Christmas tree. Its dense, feathery branches, a bright green with blueish highlights in spring, are adorned with pretty, pointed fawn buds in winter. This variety is a wonderful specimen to showcase on the terrace or in a rockery.

• Height at maturity 2 m

See the full description

Pseudotsuga menziesii Nyrany - Douglas Fir

Very slow-growing rockery specimen with a globose then pyramidal habit, in a bright green to emerald green hue, more blueish in spring.

• Height at maturity 1,20 m

See the full description

Pseudotsuga menziesii Pannenhoef - Douglas Fir

Small conifer with a twisted form, adorned with dense grey-green needles, that will not exceed 3 m in height and 2.5 m in width. Perfect on the terrace, transformed into a Christmas tree in December, or in a large rockery.

• Height at maturity 3 m

See the full description

Planting

Where to Plant the Douglas?

This conifer requires light as it is one of the first species to establish after a fire. It prefers cool climates with well-watered summers (a minimum of 700 mm of rain/year), fresh, siliceous, and deep soils but is relatively drought-tolerant, especially the variety glauca. It appears very hardy, tolerant of heat and sea spray. It accepts all types of soil, although its growth is reduced in calcareous, compacted, or poorly drained soils. Its vigorous and widely spreading roots suggest planting it away from buildings or paths, except for dwarf cultivars.

Pseudotsuga macrocarpa, notable for its cones measuring 18 to 25 cm long, thrives in dry Mediterranean climates with mild, rainy winters, similar to its native range in the Californian chaparral and Mexico.

Be aware that in the typical species, growth can reach 1 m per year after 10 years and continue like this for over 100 years! Conversely, dwarf forms have a very slow growth rate and can even withstand light pruning without issue.

When to Plant?

Prefer late summer or autumn to plant your Douglas.

How to Plant?

This plant is easy to cultivate in fairly cool climates. Opt for young plants for better establishment.

• Soak the pot in a bucket of water to thoroughly moisten it.
• Dig a wide hole at least three times wider than the root ball, as the roots remain quite superficial and spread widely.
• Add compost, a few shovelfuls of sand, and gravel to ensure good drainage around the roots. In heavy soil, planting dwarf varieties within a rockery is ideal.
• If the tree exceeds 1.5 m, staking is necessary. Plant three stakes with a diameter of 6 to 10 cm around it, 50 cm from the trunk, and tie the trunk to each with soft ties.
• Place the plant in the planting hole.
• Replace the soil and lightly firm it down.
• Water and mulch.

Entretien

• Maintain soil freshness with mulching in the following spring. Weed if necessary.
• The gardener’s work stops there unless a prolonged drought necessitates watering.
• Young Douglas plants sometimes show leaf discolouration due to aphids. Apply an insecticidal (soap, oil…) from the beginning of spring.

Multiplication

Multiplication outside of sowing is not straightforward. However, cultivars do not reproduce true to type, which is why head grafting is the technique used, but it requires a certain level of skill that we will not detail here.

Sowing

Seeds aged 10 to 20 years and well-preserved in an airtight container stored in a cool, dry place are likely to germinate.

• Perform cold moist stratification for 1 to 2 months if your seeds are old. This will allow you to sow in spring.
• Sow in light, acidic soil (sandy) directly in the nursery or in a seed tray, at a shallow depth.
• Keep the substrate moist.
• Wait until the following spring to transplant the seedlings when they start to break dormancy. Carefully plant them in individual pots that you place under a partially shaded frame.
• Place the young plants in full sun from the second year, monitoring watering.

Uses and Associations

The Douglas is a popular subject in isolation in parks, even if it is not as renowned as the cedar or the sequoia. It can highlight the edges of a grand driveway (plant them 2 m from the road), forming a majestic alignment of silhouettes that extend their low branches to the ground.

An example of association: Pseudotsuga menziesii ‘Bhiela Lhota’, Skimmia japonica, Picea abies ‘Little Gem’ and a carpet of winter heathers

Dwarf forms like the Oregon Pine Bhiela Lhota will delight collectors, as these are charming little conifers with a somewhat unpredictable but always very compact habit. Easy to care for, they can be placed in pots on the terrace, at the edge of a flowerbed, or in a rockery, alongside other dwarf conifers with a spreading habit such as Juniperus horizontalis Blue Chip, globose (Picea abies Little Gem), or columnar (Juniperus communis ‘Sentinel’), or in the company of grasses.

They harmonise well with the large stones of a rockery or a Japanese garden, as well as with the geometric lines of a contemporary garden to adorn the edges of a pool or masonry works. These dwarf forms sustainably structure a flowerbed, mark pathways, and border the terrace, easily substituting for the strong presence of trimmed boxwood or holly. The key is to play with volumes and colours.

Did you know?

The name Pseudotsuga means “false hemlock,” with hemlock referring to Tsuga, a very beautiful conifer with dense, almost feathery foliage, found in North America and the East. Its species name menziesii honours its discoverer Archibald Menzies (1754-1842), a naval officer, botanical physician, and Scottish painter.