Western red cedar(Thuja plicata 'Cuprea')

Overview

Western red cedar ‘Cuprea’ (Thuja plicata ‘Cuprea’) is a compact dwarf evergreen conifer selected from the massive forest giant of the Pacific Northwest. Hardy in USDA Zones 5 through 7, it grows very slowly into a neat, rounded globe reaching just 2 to 3 feet in its first decade, eventually maturing to 4 feet tall by 5 feet wide over several decades. Its scale-like sprays of dark green foliage are tipped with luminous creamy-yellow variegation in spring and summer that shifts to warm, glowing bronzy-copper as autumn frost arrives.

Unlike the towering 150-foot native tree, ‘Cuprea’ provides four-season architectural texture, pleasant cedar resin fragrance, and rich winter color in compact suburban beds and rockeries without outgrowing its bounds.

How to Grow

• Climate & Hardiness: Best adapted to USDA Zones 5 through 7. Originating from Pacific coastal rainforest genetics, it thrives in regions with moderate summer temperatures and regular humidity. It struggles in hot, sultry southern regions (Zones 8 and 9) without afternoon shade and consistent irrigation.
• Sunlight: Full sun to partial shade. In northern regions, full sun maximizes the bright buttery-yellow spring variegation. In hot summer climates, light afternoon canopy shade protects foliage from sunburn.
• Soil & Drainage: Prefers fertile, moist, organically rich soils with slightly acidic to neutral pH. While it tolerates heavier clay soil better than most conifers, standing stagnant water must be avoided.
• Watering & Mulch: Intolerant of severe drought. Maintain regular moisture, especially during the first two growing seasons and during dry summer spells. Apply a 2- to 3-inch layer of organic bark mulch over the root zone to conserve moisture and keep shallow roots cool.

Landscape Uses

• Rock Gardens & Troughs: Its compact dimensions, slow growth rate, and mounded form make it an ideal focal conifer alongside alpine perennials and granite boulders.
• Foundation Plantings: Sited beneath low windows, it provides year-round evergreen texture without obscuring views or needing constant shearing.
• Conifer Border Contrast: Provides striking color contrast when paired with blue spruces (Picea pungens) or dark green dwarf pines (Pinus mugo).

Potential Problems

• Drought Stress & Desiccation: Conifers native to the Pacific Northwest have shallow root systems that suffer quickly during dry continental heatwaves. Ensure consistent watering.
• Winter Wind Burn: In exposed, windy sites in Zone 5, dry winter winds can burn delicate branch tips. Shelter from prevailing winter winds.
• Bagworms & Root Rot: Monitor occasionally for bagworm caterpillars. Avoid poorly drained, waterlogged soils to prevent fungal root rot.

Frequently Asked Questions

How fast does Thuja plicata ‘Cuprea’ grow?

‘Cuprea’ is an exceptionally slow-growing dwarf conifer, averaging only 2 to 3 inches of new growth per year. It takes 10 to 15 years to reach 3 feet in diameter.

Does ‘Cuprea’ stay yellow in the winter?

No. As temperatures cool and frost arrives in autumn, the yellow-tipped foliage transitions into a warm, glowing coppery-bronze hue that persists until spring new growth emerges.

Can ‘Cuprea’ be grown in heavy clay soil?

Yes. Thuja plicata is significantly more adaptable to moist clay soils than true cedars (Cedrus) or junipers, provided water drains away and does not pool stagnantly around the crown.

Companion Plants

Pair ‘Cuprea’ with plants that appreciate moist, well-draining soil and offer textural and color contrast:

• Contrasting Conifers: Combine with blue dwarf spruces (like Picea pungens ‘Glauca Globosa’) or upright dark green yews.
• Shade & Moisture Perennials: Plant alongside blue hostas, Japanese forest grass (Hakonechloa macra), or rhododendrons in partial shade.
• Groundcovers: Underplant with creeping thyme or ajuga to create a living green carpet around its base.

Sources & Lineage

• Missouri Botanical Garden PlantFinder: Record taxon 254014 (Thuja plicata ‘Cuprea’) — botanical baseline, dimensions, and winter color shifts.
• American Conifer Society (ACS): Thuja plicata ‘Cuprea’ — cultivar registration, origin, and dwarf growth rate classification.
• Kew Plants of the World Online (POWO): Thuja plicata Donn ex D.Don (POWO: 262704-1) — species taxonomy and native range.