Thuja occidentalis 'Smaragd' – White Cedar / Emerald Green Arborvitae
Thuja occidentalis 'Smaragd' is a refined, slow-growing evergreen conifer renowned for its exceptionally neat, narrowly conical habit and strikingly vivid emerald-green foliage. Unlike many faster-growing conifers, 'Smaragd' maintains its elegant, pencil-slim silhouette with remarkably little intervention, making it one of the most popular choices for formal hedging, structured planting, and year-round garden architecture across the UK. Its name — meaning "emerald" in Danish — perfectly captures the rich, jewel-like intensity of its foliage colour, which remains brilliantly green throughout all four seasons without bronzing or dulling in cold winter weather.
Reliable, fully hardy, and exceptionally well-behaved in the garden, 'Smaragd' suits a wide range of applications from formal clipped hedges and neat garden boundaries to elegant specimen planting and container displays. For gardeners seeking a precise, architectural evergreen that stays tidy without constant attention, Thuja 'Smaragd' is an outstanding and thoroughly dependable choice.
Habit & Appearance
Form and foliage. 'Smaragd' develops a distinctively narrow, upright, conical outline that is one of its most immediately recognisable and desirable qualities. The foliage is arranged in flat, slightly twisted sprays of fine, scale-like leaves that are soft to the touch and carry a pleasant, fresh aromatic scent when brushed or trimmed. The colour is the plant's standout characteristic — a rich, deep emerald green of unusual vibrancy that holds true through spring, summer, autumn, and winter alike, showing none of the seasonal bronzing that affects many Thuja cultivars in cold weather. New growth in spring emerges in a slightly fresher, brighter shade before settling into the deep, consistent green for which this cultivar is celebrated. Left unclipped, 'Smaragd' develops naturally into a neat, dense cone with a clean, tapered apex that requires very little shaping to look immaculate.
Growth rate. 'Smaragd' is notably slower growing than cultivars such as 'Brabant' or 'Holmstrup', typically putting on 15–25 cm per year under good conditions. While this means it takes longer to reach significant height, the trade-off is a plant that holds its form far more readily and demands considerably less maintenance once established. Its compact, restrained growth is a considerable advantage in smaller gardens or where precise, long-term form is more important than rapid bulk.
Growing Conditions
Position. Thuja 'Smaragd' performs best in a position receiving full sun to partial shade. It thrives in an open, bright aspect and produces its most vibrant foliage colour in good light, though it tolerates dappled shade comfortably. It is fully hardy throughout the UK and withstands cold winters without significant damage, making it well suited to a broad range of garden environments including more exposed locations. Some shelter from the most severe, desiccating winter winds will help to keep the foliage looking its finest.
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 sites, where root health will suffer. On heavier clay soils, incorporating organic matter and improving drainage at planting will greatly assist establishment. A slightly acid to neutral soil pH is ideal, though this cultivar shows reasonable tolerance of mildly alkaline conditions too.
Planting spacing. For a dense, formal hedge, plant approximately 40–60 cm apart. The naturally compact, columnar habit of 'Smaragd' means closer spacing achieves a tight, uniform screen without plants becoming crowded over time. For specimen planting or more structured accent use, allow ample space for the plant's natural conical form to develop fully without competition.
Care
Watering. Water regularly and thoroughly during the first growing season after planting to support strong root establishment. This is especially important during dry spells in spring and summer when young plants are most vulnerable to moisture stress. Once fully established, Thuja 'Smaragd' develops a reasonable degree of drought tolerance, though supplementary watering during prolonged dry periods will always benefit the plant's appearance and health.
Feeding. Apply a balanced, slow-release granular fertiliser in early spring to promote steady, healthy growth and maintain the richness of the foliage colour. A feed formulated for conifers or evergreen hedging plants is well suited to this purpose. Mulching around the base with bark chippings or garden compost each spring will help to conserve soil moisture, suppress weeds, and protect the root zone from temperature extremes.
Pruning. One of the most appealing qualities of 'Smaragd' is its naturally disciplined habit — many gardeners find that little or no trimming is required to keep it looking immaculate, particularly when grown as a specimen. Where a formal hedge or precisely defined line is desired, a single light trim once a year in late spring or early summer is generally sufficient to keep growth neat and well-defined. A second, light pass in late summer can be carried out if additional tidiness is required. As with all Thuja cultivars, avoid cutting back hard into old, bare wood, as the species does not regenerate readily from stems that have lost active foliage. Regular, modest trimming from an early stage consistently produces the most attractive and densely furnished results.
Ideal Uses
Formal hedging – The narrow, self-shaping habit and consistent foliage colour make 'Smaragd' one of the finest choices available for precise, formal hedge lines that hold their shape with minimal effort.
Garden boundaries and screening – Dense, year-round
