American arborvitae (Thuja occidentalis 'Smaragd')

Overview

The American arborvitae cultivar, Thuja occidentalis ‘Smaragd’, offers gardeners a striking, narrowly pyramidal form ideal for formal landscapes and screening without excessive width. This specific selection maintains dense, bright green, scale-like foliage year-round, giving it the common name ‘Emerald Green Arborvitae’ in many settings due to its vibrant color. As a needled evergreen, Thuja occidentalis ‘Smaragd’ provides essential structure and color during the winter months, making it a consistent performer across USDA Zones 2 through 7.

Valued for its low maintenance requirements and relatively slow growth, this variety of American arborvitae is highly adaptable once established. Gardeners appreciate its resistance to many common landscape issues, although specific cultural needs regarding moisture and sunlight must be met for optimal density. The compact nature of Thuja occidentalis ‘Smaragd’ makes it a superior choice over larger, less refined native specimens when space is a consideration.

Functionally, the dense growth habit of the Thuja occidentalis ‘Smaragd’ lends itself perfectly to vertical accents or tightly spaced privacy screens where classic, formal evergreen texture is desired. Its native lineage provides inherent toughness, reflected in its hardiness and ability to tolerate challenging urban conditions when sited correctly.

Fast Facts

• Plant Family: Cupressaceae
• Plant Type: Needled evergreen
• Hardiness Zones: USDA Zones 2-7
• Size at Maturity:
  • Height: 12-14 ft
  • Spread: 3-4 ft
• Bloom Time: Non-flowering
• Bloom Description: Non-flowering
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Low

How to Grow

Planting Thuja occidentalis ‘Smaragd’ is best done in spring or fall when temperatures are moderate, ensuring the root ball establishes before environmental extremes hit. Locate specimens where they receive full sun, though light afternoon shade is tolerated, especially in hotter climates. This American arborvitae thrives in average, medium moisture, well-drained soils. While it possesses a somewhat wide tolerance range, it performs best in moist, neutral to alkaline loams.

Consistent moisture is critical, as this cultivar is intolerant of dry conditions. Water regularly, especially during the first few growing seasons, to encourage deep root development. Once established, maintain a medium watering schedule matching natural rainfall patterns. Pruning is generally minimal; focus on removing any damaged or dead interior branches only, as heavy shearing can compromise the natural shape of the Thuja occidentalis ‘Smaragd’.

Avoid planting Thuja occidentalis ‘Smaragd’ in overly exposed, windy sites, as these locations increase the risk of winter desiccation. Protection from strong winter winds can help mitigate potential foliage burn. Furthermore, avoid planting in full shade, as this drastically reduces the desired foliage density, resulting in a sparser, less attractive specimen.

Landscape Uses

The primary structural use for the American arborvitae ‘Smaragd’ is creating defined, formal screening or hedging. Planted closely together, these narrow evergreens form an impressive year-round visual barrier that remains manageable in height and spread compared to many other screening conifers. Their strong vertical habit also makes them excellent background plants in foundation plantings, adding necessary height behind lower perennial beds.

Beyond mass plantings, individual Thuja occidentalis ‘Smaragd’ specimens serve beautifully as formal accents flanking entryways or defining transitional spaces within a garden design. Their compact, bright green cones provide year-round focal points. For best results, group these evergreens with contrasting textures, such as broadleaf deciduous shrubs or lighter-colored ornamental grasses, allowing the glossy, fine texture of the American arborvitae to truly stand out.

Standout Features

Noteworthy Characteristics

Thuja occidentalis, commonly known as American arborvitae, is a dense, conical to narrow-pyramidal, often single-trunked, evergreen tree native to eastern and central Canada. The cultivar ‘Smaragd’ is specifically noted for its semi-dwarf, compact habit, featuring glossy bright green, scale-like foliage in flat sprays. Urn-shaped cones mature in autumn to reddish brown; most often, this variety is seen as a manageable 7 to 15-foot shrub with a narrow spread.

Tolerances

• Clay Soil
• Black Walnut
• Air Pollution

Potential Problems

Foliage quality in Thuja occidentalis ‘Smaragd’ can be impacted by several common issues. Leaf blight may cause leaf spotting and eventual dropping, which requires watchful monitoring. Canker is another potential fungal issue to guard against through proper air circulation during planting.

Pest pressure is usually low, but gardeners should watch for common needle-feeding insects. Leaf miners occasionally damage leaf tips, and occasional infestations of bagworms, mealybugs, scales, and spider mites may occur. Proactive inspection aids early treatment.

Winter weather poses specific risks to this American arborvitae. Exposed sites can lead to winter burn, appearing as yellow-brown discoloration on the foliage. More significantly, the dense branches are susceptible to structural damage and stem breakage from heavy accumulations of ice and snow, necessitating structural support in severe winter climates.

Frequently Asked Questions

What hardiness zones is American arborvitae (Thuja occidentalis ‘Smaragd’) suitable for?

Thuja occidentalis ‘Smaragd’ is highly cold-hardy, succeeding well in USDA Zones 2 through 7.

How large does American arborvitae (Thuja occidentalis ‘Smaragd’) grow?

This compact cultivar typically matures to a height between 12 to 14 feet, maintaining a narrow spread of only 3 to 4 feet wide.

What sun exposure does American arborvitae (Thuja occidentalis ‘Smaragd’) need?

This needled evergreen requires full sun exposure for best density, although it can tolerate partial shade, provided it avoids deep, dark shade.

When does American arborvitae (Thuja occidentalis ‘Smaragd’) bloom?

Thuja occidentalis ‘Smaragd’ is non-flowering; it is valued for its year-round foliage rather than floral display, producing small, inconspicuous cones instead.

Conclusion

The Thuja occidentalis ‘Smaragd’ remains a cornerstone plant for achieving structured, low-maintenance evergreen appeal in modern and formal landscapes. Its compact size and brilliant glossy green color ensure that this American arborvitae provides excellent screening and accent value across a wide cold hardiness range. Before planting, ensure your site offers reliable moisture and full sun exposure to maximize the beauty of your Emerald Green Arborvitae.

Companion Planting

When designing borders or screens using Thuja occidentalis ‘Smaragd’, pairing them with contrasting textures enhances their visual impact. Consider planting them alongside plants with broad, maplesque leaves, such as certain varieties of Hydrangea or Spirea, which offer soft movement against the stiff structure of the evergreen. Lighter-colored deciduous trees, like Amelanchier (Serviceberry), can provide dappled shade during the intense summer heat, benefiting the subtly shaded portions of the American arborvitae.

For seasonal color interest near foundation plantings of Thuja occidentalis ‘Smaragd’, utilize spring bulbs like Daffodils or Tulips that naturally die back before the evergreen’s base draws the eye. In summer, low-growing, mounding perennials with silver or gold foliage, such as Artemisia or some Sedums, offer continuous textural contrast at the base without competing for vertical space.

Seasonal Care Calendar

Spring: This is the ideal time for any corrective pruning on your Thuja occidentalis ‘Smaragd’, removing any winter-damaged tips or interior debris before active growth begins. Apply a slow-release fertilizer formulated for acid-loving or evergreen plants early in the growing season if soil fertility is questioned.

Summer: Focus entirely on consistent watering. Since this variety is intolerant of drought, supplement rainfall deeply, especially during dry spells when the soil is moist but not saturated. Monitor for signs of bagworm activity, which are easily managed when populations are small.

Autumn: Reduce supplemental watering as temperatures drop. Prepare for winter by ensuring the base of the plant is well-moisturized before the ground freezes solid; this helps mitigate winter burn. Minor staking or guying can be considered for extremely tall specimens to guard against heavy snow load damage.

Winter: Protect young or exposed Thuja occidentalis ‘Smaragd’ specimens from prevailing winter winds using burlap screens or snow fencing installed on the windward side to minimize desiccation and foliage burn.