Bartlett Tree Experts: Western Red Cedar

Thuja spp

Species and hybrid varieties in the genus Thuja are commonly used in hedges, screens, and as specimen plants. Some common names of well used species and varieties are ‘arborvitae’ (T. occidentalis), ‘western red cedar’ (T. plicata), or hybrids such as ‘Green Giant’, ‘Pyramidalis’, or ‘Smaragd’. Commonly referred to as ‘cedar hedges’ in the PNW and B.C.

Culture
Concerns
Management

Culture for Western Red Cedar

Often found in dense linear plantings for hedges and screens. Most Thuja species require full sun, ample moisture, and highly organic, slightly acidic soils. Dense and compact when sheared, most species will form a loose and drooping habit when not pruned. Often planted too deep.

Concerns about Western Red Cedar

Poor planting (depth, burlap not removed) is a very common cause of decline and death of individual plants in hedges. Poorly drained soils or deep planting will lead to Phytophthora root and crown diseases. Spider mites cause general bronzing of foliage. Tip moths and arborvitae leafminer are a common causes of tip browning, as is a fungal disease known as “Keithia blight”. Bark beetles may also attack stressed plants.

Management Practices for Western Red Cedar

Excavate root collars of deeply planted trees, and check for burlap or wire cage left on root ball at planting. Excellent candidate for root invigoration due to shallow root system and preference for organic soils. Treat preventatively to manage Phytophthora on wet, poorly drained, or clay soils. Treat for mites, tip moths, and Keithia blight as warranted. When shearing hedges, maintain the lower canopy slightly wider than the top so that the bottom of the hedge is not shaded out by the upper canopy.