Thuja occidentalis 'Smaragd' – Emerald White Cedar
Thuja occidentalis 'Smaragd' is a refined, slow-growing evergreen conifer prized above all for the exceptional brilliance of its foliage. The name 'Smaragd' is the Danish word for emerald, and it is entirely apt — the dense, flat sprays of scale-like leaves hold a vivid, jewel-bright green throughout all four seasons, resisting the bronze or yellow tints that affect many other conifers in winter. With its elegant, slender columnar habit and naturally neat, self-maintaining form, 'Smaragd' has become one of the most widely admired and planted conifers in the UK and across Europe, valued equally as a formal hedging plant, a structured specimen, and a year-round garden focal point.
Slower-growing and more compact than vigorous hedging conifers such as 'Brabant' or 'Holmstrup', 'Smaragd' is a conifer that rewards patience with exceptional quality — a polished, architectural presence that requires very little maintenance to look its best. Whether used as a formal clipped hedge, an avenue of matched specimens, or a single vertical accent in a border, it brings a consistency of colour and shape that few evergreens can match.
Habit & Appearance
Form and foliage. 'Smaragd' develops a distinctly narrow, tightly columnar to slightly conical outline that remains naturally well-proportioned and symmetrical without heavy intervention. The foliage is carried in dense, flattened, overlapping sprays of fine, scale-like leaves with a smooth, slightly glossy texture and a faint, pleasant, resinous fragrance when cut or brushed. The defining characteristic of this cultivar is the remarkable stability of its foliage colour — a rich, saturated emerald green that persists with very little change through autumn and winter, when many competing conifers take on bronzy or yellowish tones. New spring growth emerges as a fresh, slightly brighter green before settling into the characteristic deep emerald through the summer. Left unpruned, mature plants typically reach 3–5 metres in height over many years, forming a graceful, slender column that makes an outstanding permanent feature in a well-planned garden.
Growth rate. 'Smaragd' is notably slower-growing than many other Thuja occidentalis cultivars, typically adding 15–25 cm per year under good conditions. While this means patience is required during establishment, the slower pace results in exceptionally dense, well-knit foliage, a naturally refined silhouette, and a plant that needs far less maintenance trimming than faster-growing alternatives. It is a long-lived, durable conifer that rewards an unhurried approach.
Growing Conditions
Position. Thuja 'Smaragd' performs best in a position that receives full sun to partial shade. An open, sunny aspect produces the densest foliage and the most vibrant colour, but it adapts well to dappled shade and performs reliably alongside walls, fences, or under the light canopy of nearby trees. It is fully hardy throughout the UK and shows good tolerance of exposed conditions, though a degree of shelter from the harshest winds will help it maintain its characteristic neat outline and minimise any winter foliage browning at the tips.
Soil. Adaptable to most fertile, reasonably well-drained soils, including clay, loam, and sandy ground. 'Smaragd' tolerates moderately moist conditions but will not perform well in permanently waterlogged or poorly drained soil — good drainage is important, particularly through the winter months. On heavier soils, incorporating organic matter and grit at planting will improve drainage and encourage healthier root development. A slightly acid to neutral pH is ideal, though the plant copes adequately on mildly alkaline ground.
Planting spacing. For a formal, close-knit hedge, plant approximately 50–60 cm apart. For a more structured avenue or paired specimen planting, individual plants can be spaced more generously to allow the full columnar outline of each plant to be appreciated. For windbreaks or informal screening, spacing of 60–80 cm is appropriate, as plants will gradually fill and merge over time.
Care
Watering. Regular, thorough watering during the first growing season after planting is essential to support healthy establishment. This is particularly important during dry spells in spring and summer, and during any unseasonably warm or dry periods in the plant's first couple of winters. Once fully established, 'Smaragd' develops a reasonable degree of drought tolerance and will generally manage well without supplementary watering except during prolonged dry conditions.
Feeding. Apply a balanced, slow-release granular fertiliser in early spring each year to support steady, healthy growth. A product formulated for conifers or hedging plants is well suited to this purpose. Mulching around the base annually with bark chippings or garden compost will help conserve soil moisture, moderate root temperature, and suppress competing weeds — all of which contribute to stronger, more consistent growth.
Pruning. One of the great practical advantages of 'Smaragd' is that its naturally tidy, symmetrical form requires very little corrective trimming to maintain. A single light clip once a year — ideally in late spring after the first flush of new growth has hardened off, or in late summer — is generally sufficient to keep a hedge or specimen looking crisp and well-defined. Avoid cutting back hard into old, bare wood, as Thuja does not regenerate reliably from stems that have lost their green foliage. Because 'Smaragd' grows at a measured pace, even minimal annual trimming produces consistently neat, dense results without the need for frequent intervention.
Ideal Uses
