Western red cedar (Thuja plicata)

Overview

The Western red cedar, scientifically known as Thuja plicata, is a towering, majestic needled evergreen native to the Pacific Northwest. Gardeners value this species for its highly aromatic, scale-like dark green foliage and its impressive stature, making it a dominant feature in any landscape where space permits. When crushed, the foliage releases a distinct, pleasing scent, marking it as a true giant of the cypress family.

Though it can become immense in its native habitat, cultivated varieties of Thuja plicata are commonly managed for use as imposing screens or substantial specimen trees in suitable climates. They thrive best where summers remain cool and consistently moist, demanding protection from prolonged dry spells typical of hotter inland regions. Proper siting is crucial to maximize the natural beauty of this long-lived conifer.

This species provides year-round structure and visual interest, growing reliably across hardiness zones 5 through 7. For optimal performance, ensure Thuja plicata is placed in a location where its root system can access adequate water while benefiting from well-drained soil conditions.

Fast Facts

• Plant Family: Cupressaceae
• Plant Type: Needled evergreen
• Native Range: Western North America
• Hardiness Zones: USDA Zones 5-7
• Size at Maturity:
  • Height: 50-70 ft
  • Spread: 15-25 ft
• Bloom Time: Non-flowering
• Bloom Description: Non-flowering
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Medium

How to Grow

Planting Thuja plicata should ideally occur in the spring or fall to allow the root system to establish before experiencing temperature extremes. Locate this tree where it will receive full sun to light afternoon shade, particularly in hotter zones. The species insists upon moist, fertile, well-drained soils; avoid heavy, compacted areas lacking adequate drainage, as this species is intolerant of dry conditions.

Once established, the Western red cedar requires medium water input, especially during dry summers. Consistent moisture is key to sustaining its deep green color and vigorous growth rate. While heavy fertilization is usually unnecessary for mature trees, ensuring the soil retains adequate moisture is more critical than supplementing nutrients.

Pruning should be minimal, mainly reserved for shaping young trees intended for hedging or removing any dead or damaged limbs immediately. Avoid heavy shearing of mature western red cedar, as this can negatively affect their natural form. Gardeners in regions characterized by hot, dry summers, such as the St. Louis area mentioned in observational notes, must be aware that the environmental mismatch may cause the plant to struggle.

Landscape Uses

The versatility of Thuja plicata allows it to serve multiple functional and aesthetic roles on larger properties. Its rapid, dense growth makes it an excellent choice when a substantial, permanent hedge or screen is desired for privacy or windbreaking purposes. Young trees can be closely spaced and easily pruned into formal boundaries, while mature specimens excel as large specimen trees defining expansive lawns or providing deep, dark backdrops to brighter plantings.

Consider using the Western red cedar in rain garden settings, given its preference for moist soil conditions, provided the area does not become swampy or waterlogged continuously. For design contrast, pair the deep green texture of the Thuja plicata foliage with plants that offer lighter greens, finer textures, or bright seasonal flower colors.

Its imposing structure also lends itself well to framing entrances or marking transitions between different zones of a landscape. When used as a background element, the rich, fibrous reddish-brown bark adds textural interest, especially during winter months after the foliage has darkened slightly.

Standout Features

Noteworthy Characteristics

Thuja plicata, commonly called western red cedar or giant red cedar, is native to the Pacific Northwest where it is typically found in cool but moist forest areas and bottomlands from southern Alaska along the Pacific coast to northern California and in the northern Rockies from British Columbia to Montana. This is the largest tree in the cypress family, growing in its native habitat to 100-200’ tall and living from 400 to 1000+ years. It features horizontal branching with sprays of scale-like dark green foliage that is aromatic when crushed, alongside fibrous, aromatic, reddish-brown bark and small, upright seed cones.

Tolerances

• Clay Soil
• Black Walnut

Potential Problems

The Western red cedar generally exhibits good resistance, reporting no serious insect or disease problems when grown in its preferred environment. However, vigilance is required; issues like Bagworm infestation or various root rots may occur, usually linked to stress or inappropriate growing conditions. If you notice dieback or thinning, immediately check soil moisture levels, as intolerance to dry conditions is a known weakness.

Gardeners situated outside the ideal coastal environment should monitor for signs of heat stress, which can weaken the plant and make it more susceptible to secondary invaders. If problems like fungal rots appear, improve air circulation and reduce soil saturation immediately. For specific pest issues like bagworms, manual removal or targeted insecticide application, timed correctly for the life cycle, offers management options.

Frequently Asked Questions

What hardiness zones is Western red cedar suitable for?

The Thuja plicata prefers USDA Zones 5 through 7.

How large does Thuja plicata grow?

When mature, this Western red cedar typically reaches heights between 50 and 70 feet, with a spread of 15 to 25 feet.

What sun exposure does Western red cedar need?

This needled evergreen performs best in full sun to part shade conditions.

When does Western red cedar bloom?

This species is non-flowering and does not produce traditional blooms; it develops small, upright cones instead.

Conclusion

The robust structure and fragrant, evergreen foliage make Thuja plicata a highly valuable addition for creating privacy screens or anchoring large garden spaces. As the magnificent Western red cedar, it offers year-round screening, provided its needs for medium water and well-drained soil are met. Always confirm that your local hardiness zone falls within USDA 5-7 before planning your planting for the best success.

Companion Planting

Choosing companions for Thuja plicata should focus on plants that appreciate similar moisture levels and potentially offer textural contrast. Since the Western red cedar thrives in moist, fertile soil, pairing it with moisture-loving hydrangeas or large ferns that enjoy dappled shade beneath its canopy can create a lush, woodland effect. Avoid extremely drought-tolerant plantings near the base of the cedar, as their competition for surface water can stress the conifer.

When designing a screen row, consider planting deciduous shrubs with bright winter stems, such as certain dogwood varieties, whose color will become prominent against the deep green of the Thuja plicata during the dormant season. This strategy ensures visual interest throughout the year, utilizing the structure provided by the cedar.

Design Ideas for Screens and Specimens

For creating a high-impact privacy screen, space younger Thuja plicata trees approximately 10 to 15 feet apart on center, allowing them room to mature into overlapping foliage masses. If the goal is a formal hedge, prune consistently when young to encourage denser growth, though be mindful not to over-prune past the green foliage into old wood. As a specimen, allow the tree to assume its natural, pyramidal form, placing it where it can be viewed from a distance to appreciate its scale.

In larger, naturalistic landscapes, the Western red cedar acts as an excellent vertical anchor against lower-growing evergreens or broadleaf rhododendrons, mimicking the native Pacific coastal forest edge. Its ability to tolerate clay soil means it can successfully anchor wetter sections of the yard where other conifers might fail due to poor drainage.