Thuja

Thuja is a genus of evergreen conifers in the cypress family Cupressaceae, commonly known as arborvitae. The genus comprises several species native to North America and East Asia, including Thuja occidentalis (Eastern arborvitae), Thuja plicata (Western redcedar), Thuja standishii (Japanese arborvitae), Thuja orientalis (Oriental arborvitae), and Thuja sutchuenensis (Szechuan arborvitae), as well as numerous cultivated hybrids and cultivars. They are widely grown in gardens for their dense foliage and ability to form screens and hedges.

Thuja are typically medium to large evergreen trees or shrubs with a conical to columnar habit. They have flat sprays of scale-like leaves in opposite decussate pairs and emit a characteristic scent when crushed. Cones are small, oval to oblong, 8–18 mm long, with numerous scales; they brown at maturity and release winged seeds. Wood is light and moderately durable, often used for decorative purposes in regions where the species occur naturally.

Habitat and cultivation: Thuja species are native to forests of North America and East Asia but are cultivated worldwide. They prefer fertile, well-drained soils and generally perform best in full sun to partial shade. They range from slow-growing to fast-growing cultivars, with mature sizes from compact shrubs to tall trees. They are commonly used as ornamental specimens, hedges, and privacy screens. Popular cultivars include Thuja occidentalis 'Emerald Green' and 'Smaragd', and the large evergreen 'Green Giant' (a T. standishii x T. plicata hybrid).

Propagation and pests: Propagation is by seed or cuttings; cultivars are typically propagated by cuttings or grafting to preserve traits. Thuja can be affected by pests such as bagworms, spider mites, and scale, and by diseases including cedar-apple rust and root rot. They are generally hardy in temperate regions but may suffer from winter burn in hot, dry winters.