Thuja occidentalis 'Smaragd' – White Cedar / Emerald Green Arborvitae
Thuja occidentalis 'Smaragd' is a refined, slow-growing evergreen conifer renowned for its strikingly narrow, pencil-like form and the exceptional brilliance of its foliage. Producing dense, flattened sprays of vivid emerald-green leaves that hold their jewel-bright colour with remarkable consistency throughout every season of the year, 'Smaragd' is widely regarded as one of the finest conifers available for formal garden use. Its elegant, naturally symmetrical silhouette and restrained growth make it equally suited to structured hedging, accent planting, and container growing, offering year-round presence without the management demands of faster-growing alternatives.
Where other conifers may dull or bronze in cold weather, 'Smaragd' maintains its vivid colouring even through the depths of winter — a quality that has made it a perennial favourite among gardeners seeking lasting evergreen impact with minimal intervention. Fully hardy, versatile, and consistently well-behaved, it is an outstanding choice for gardens where precision, colour, and long-term reliability matter.
Habit & Appearance
Form and foliage. 'Smaragd' develops a strongly upright, tightly columnar to narrowly conical habit that remains beautifully self-contained and symmetrical as the plant matures. The foliage is carried in flat, overlapping sprays of fine, scale-like leaves with a soft texture and a faint, pleasant aromatic scent when cut or brushed. Unlike the majority of conifers — including many of its Thuja relatives — 'Smaragd' holds its distinctive, vivid emerald-green colouring with exceptional steadfastness through autumn and winter, showing little to no bronzing even during prolonged cold spells. This reliable winter colour is one of the cultivar's most celebrated and commercially valued qualities. Left to grow freely, mature plants will typically reach around 3–4 metres in height over many years, while maintaining a naturally slender and elegant outline throughout.
Growth rate. 'Smaragd' is a slow to moderate grower, typically putting on around 15–20 cm per year under good conditions. While this means it establishes screening more gradually than faster-growing alternatives, its slower pace also means the plant retains a naturally neat, manageable form with very little intervention required — a genuine advantage for those seeking a low-maintenance, long-lived garden conifer.
Growing Conditions
Position. Thuja 'Smaragd' performs best in a position that receives full sun to partial shade. It thrives in an open, bright aspect where it will produce the densest foliage and most vibrant colour, but it tolerates dappled or light shade comfortably. It is fully hardy throughout the UK and copes well with moderate exposure, though a degree of shelter from the most severe, desiccating winds will help the foliage maintain its best appearance, particularly in winter.
Soil. Adaptable to most fertile, reasonably well-drained soils, including clay, loam, and sandy ground. 'Smaragd' tolerates moderately moist conditions better than many conifers but will not perform well in permanently waterlogged or poorly drained soil. Incorporating organic matter and improving drainage on heavier soils at planting time will support stronger, healthier establishment. A slightly acid to neutral soil pH is ideal, though this cultivar copes reasonably well with mildly alkaline conditions.
Planting spacing. For a formal, close-knit hedge or screen, plant approximately 40–60 cm apart. This spacing will encourage the plants to knit together into a dense, uniform barrier while allowing each individual plant to develop its characteristic narrow form. For use as accent or specimen plants, space more generously to allow the elegant silhouette of each plant to be fully appreciated. In containers, a single plant per pot is recommended to avoid root competition.
Care
Watering. Water regularly and thoroughly during the first growing season after planting to encourage strong root establishment. This is particularly important during warm, dry periods in spring and summer. Once well established, 'Smaragd' develops a reasonable degree of drought tolerance, though supplementary watering during extended dry spells will always be beneficial, especially for hedging plants growing in competition with one another.
Feeding. Apply a balanced, slow-release granular fertiliser in early spring to support healthy, consistent growth. A fertiliser formulated for conifers or hedging plants is well suited to this purpose. An annual mulch of bark chippings or garden compost applied around the base in spring will help retain soil moisture, suppress weeds, and protect the root zone from temperature fluctuation.
Pruning. One of 'Smaragd's' most appealing qualities is its naturally symmetrical, self-maintaining habit, which requires very little clipping to keep looking immaculate. A single, light trim once a year — ideally carried out in late spring or early summer after the first flush of new growth — is typically all that is needed to maintain a crisp, tidy outline. A second, lighter pass in late summer can be made if needed to tidy any late-season extension growth. As with all Thuja, avoid cutting back hard into old, brown, foliage-free wood, as the plant will not regenerate from bare stems. Plants left entirely untrimmed will maintain an attractive, naturally refined form without any intervention at all.
Ideal Uses
Formal hedging and screening – Naturally narrow, dense growth provides year-round evergreen coverage and clips to a precise, elegant hedge line.
Specimen and accent planting – The distinctive, slender column of 'Smaragd' makes a striking vertical accent in borders, entranceways, and open lawn settings.
Paired and symmetrical planting – Flanking doorways,
