Thuja occidentalis 'Smaragd' – Emerald Green Arborvitae
Thuja occidentalis 'Smaragd' is a refined, slow-growing evergreen conifer celebrated for its strikingly vivid emerald green foliage and elegantly narrow, pyramidal habit. Unlike many faster-growing hedging conifers, 'Smaragd' is valued precisely for its restraint — maintaining a naturally neat, compact form that requires very little intervention to keep looking immaculate. Its rich, jewel-toned foliage holds its brilliant colour reliably through all four seasons, including winter, when many conifers fade to dull bronze or yellow-green tones. This exceptional colour retention is one of the key qualities that sets 'Smaragd' apart and has made it one of the most admired ornamental conifers available.
Fully hardy, adaptable to a wide range of soils, and equally at home in formal gardens, contemporary planting schemes, or classic structured borders, Thuja 'Smaragd' is as versatile as it is beautiful. Whether used as an elegant specimen, planted in pairs to frame an entrance, or arranged in a row to form a precise, low-maintenance screen, it delivers year-round architectural interest with outstanding consistency.
Habit & Appearance
Form and foliage. 'Smaragd' develops a cleanly defined, narrow pyramidal to columnar outline that remains tight and well-proportioned naturally as the plant matures, with very little tendency to sprawl or open up at the base. The foliage is carried in flat, upright sprays of fine, scale-like leaves with a smooth, slightly glossy texture and a pleasant, resinous fragrance when handled. The colour is exceptional — a deep, vivid emerald green that remains strikingly consistent through spring, summer, autumn, and winter alike, without the bronzing or discolouration that affects many other arborvitae cultivars in cold weather. New spring growth emerges in a fresh, bright green before settling into the characteristic rich emerald tone through summer and beyond. Mature plants form a graceful, slender spire that fits comfortably into even relatively confined spaces.
Growth rate. 'Smaragd' is a slow to moderate grower, typically putting on around 15–20 cm per year under good conditions. This measured pace is one of its principal advantages for gardeners seeking a low-maintenance, long-term planting — the plant settles naturally into its intended shape and size without demanding frequent clipping to keep it in check. Ultimate height at maturity is typically in the range of 3–5 metres, though this is reached gradually over many years.
Growing Conditions
Position. Thuja 'Smaragd' performs best in a position receiving 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 shade reasonably well. It is fully hardy throughout the UK and shows good resilience to cold temperatures and moderate wind exposure, making it suitable for a wide range of garden settings. Avoid positioning in deep, permanent shade, where growth may become sparse and the foliage less vivid.
Soil. Adaptable to most fertile, reasonably well-drained soils, including loam, clay, and sandy ground. 'Smaragd' tolerates moderately moist conditions but will not thrive in waterlogged or persistently saturated soil. On heavier clay ground, incorporating organic matter and ensuring good drainage at planting time will encourage healthier, stronger establishment. A slightly acid to neutral pH is ideal, though this cultivar copes well with mildly alkaline soils too.
Planting spacing. For a formal, close-clipped screen or hedge, plant approximately 60–80 cm apart. For a looser, more naturalistic arrangement or a line of individual specimens, spacing of 1–1.5 metres apart allows each plant to develop its full natural outline without crowding. For flanking an entrance or creating symmetrical pairs, a single plant on each side placed at an appropriate distance from the threshold is the classic approach.
Care
Watering. Water regularly and thoroughly during the first full growing season after planting to support strong root establishment. This is particularly important during warm, dry spells in spring and summer. Once well established, Thuja 'Smaragd' develops reasonable drought tolerance and will generally manage on natural rainfall, requiring supplementary watering only during prolonged dry periods.
Feeding. Apply a balanced, slow-release granular fertiliser in early spring each year to support healthy, steady growth. A feed formulated for conifers or ornamental evergreens is well suited to this purpose. Mulching around the base annually with bark chippings or garden compost helps retain soil moisture, suppress weeds, and protect the root zone from temperature fluctuations.
Pruning. One of 'Smaragd's' most appreciated qualities is how little pruning it demands. Its naturally tidy, self-organising habit means that many gardeners find little or no trimming is needed to maintain an attractive, well-proportioned shape. Where a formal hedge or precise outline is desired, a single light trim once a year — ideally in late spring or early summer after the first flush of new growth — is generally all that is required. As with all Thuja, avoid cutting back hard into old, brown wood that has lost its foliage, as this species does not regenerate readily from bare stems. Light, regular trimming from an early stage always produces the neatest, most satisfying results.
Ideal Uses
Formal specimen planting – The slender, symmetrical outline of 'Smaragd' makes it an outstanding architectural specimen in borders, courtyards, and formal garden schemes.
Entrance framing – Planted in pairs, 'Smaragd' creates a classic, elegant frame for doorways, gateways, and garden entrances.
