American arborvitae (Thuja occidentalis 'Nigra')

Overview

The Thuja occidentalis ‘Nigra’, commonly known as American arborvitae, is a highly valued needled evergreen celebrated for its densely packed, dark green foliage. This cultivar maintains excellent color retention throughout the winter, offering consistent year-round visual interest in the landscape. Its naturally conical shape lends itself perfectly to formal settings requiring structure and screening capability.

As a robust cultivar of American arborvitae, ‘Nigra’ proves relatively adaptable once established, though it thrives best in moisture-retentive, neutral to alkaline soils. Gardeners appreciate its low maintenance requirements, allowing it to function effectively as a backdrop or living privacy screen without constant intervention.

This specific variety typically matures at a manageable 20 to 30 feet tall, maintaining a narrower profile (5 to 10 feet wide) compared to the species, which makes it an excellent vertical accent. The dark green, scale-like foliage is aromatic, confirming the desirable characteristics of the Thuja occidentalis lineage.

Fast Facts

• Plant Family: Cupressaceae
• Plant Type: Needled evergreen
• Hardiness Zones: USDA Zones 3-7
• Size at Maturity:
  • Height: 20-30 ft
  • Spread: 5-10 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 ‘Nigra’ should ideally occur in spring or early fall to allow the root system to establish before temperature extremes. Ensure the planting location receives full sun, though partial afternoon shade is beneficial in the hottest summer climates. This American arborvitae requires average, medium moisture, well-drained soils, preferring neutral to alkaline loams. Avoid planting in areas prone to standing water or severe drought.

Watering is crucial during the first few seasons immediately following planting. While established specimens require medium water, aiming for consistent moisture is key; they are intolerant of dry conditions. Fertilizing is seldom necessary if planted in adequate soil, but a balanced, slow-release evergreen fertilizer in early spring can promote vigorous growth if the soil is poor. Minor pruning can be performed in early spring to shape the hedge or remove errant branches.

When siting your Thuja occidentalis ‘Nigra’, remember that avoiding exposed, windy sites is important, especially during winter. Too much shade will reduce foliage density significantly. Site preparation should focus on ensuring excellent drainage, as poor drainage is a common cause of decline in this species.

Landscape Uses

The primary role of Thuja occidentalis ‘Nigra’ in landscape design is functional boundary creation. Due to its upright, conical habit and relatively narrow spread, it excels when used for screens and hedges, providing structure and privacy year-round. It forms an exceptionally dense barrier compared to many other evergreens.

Beyond screening, this American arborvitae works well as formal plantings flanking entryways or as tall foundation plantings along the side of a building where height is needed. For a classic, formal look, plant specimens in symmetrical pairs. When used as a specimen plant, ensure adequate space for its mature height, allowing the natural conical shape to develop fully.

Consider pairing the dark green foliage of Thuja occidentalis ‘Nigra’ with plants offering contrasting color or texture, such as deciduous grasses or bright-leafed shrubs, to break up large swaths of evergreen massing. Its tolerance for diverse conditions also makes it suitable for somewhat challenging urban environments.

Standout Features

Noteworthy Characteristics

Thuja occidentalis, commonly known as American arborvitae, Eastern arborvitae, Eastern white cedar or Northern white cedar, is a dense, conical to narrow-pyramidal (sometimes maturing to broad-pyramidal), often single-trunked, evergreen tree native to eastern and central Canada. The cultivar ‘Nigra’ specifically features flattened sprays of dark green foliage that retain good green color throughout the year, including winter. While the species can reach substantial heights in the wild, this selection typically maxes out around 20-30 feet tall in cultivation, offering a reliably formal presence.

Tolerances

• Clay Soil
• Black Walnut
• Air Pollution

Potential Problems

Foliage spotting and dropping can sometimes indicate leaf blight, which benefits from good air circulation and avoiding overhead watering. Watch carefully for signs of canker, which affects the branches and stems. Occasional insect pests include leaf miners, which damage leaf tips, as well as common visitors like bagworms, mealybugs, scales, and spider mites.

For winter protection, especially in exposed sites, foliage may suffer from winter burn, turning yellow-brown as moisture loss exceeds uptake. Furthermore, the dense branching structure of Thuja occidentalis ‘Nigra’ makes it susceptible to damage or stem breakage from heavy ice and snow accumulation; gently shaking snow from boughs after storms can mitigate damage.

Frequently Asked Questions

What hardiness zones is American arborvitae suitable for?

Thuja occidentalis ‘Nigra’ is hardy and adaptable across USDA Zones 3 through 7.

How large does Thuja occidentalis ‘Nigra’ grow?

This cultivar typically reaches a mature height between 20 and 30 feet tall, with a spread of 5 to 10 feet wide.

What sun exposure does American arborvitae need?

This evergreen performs best when afforded full sun, but it will tolerate part shade, appreciating slight afternoon protection in very hot regions.

When does American arborvitae bloom?

Thuja occidentalis ‘Nigra’ is a needled evergreen and is non-flowering; it does not produce noticeable flowers or showy fruits.

Conclusion

The Thuja occidentalis ‘Nigra’ stands out as a reliable, low-maintenance choice for gardeners needing year-round screening and vertical accent in USDA Zones 3 to 7. Its deep green, dense foliage solidifies its status as a premier American arborvitae selection. Confirm your site conditions align with its need for medium moisture and full sun before planting this versatile evergreen.

Companion Planting

Selecting companions rich in contrasting color or texture enhances the visual impact of the dark green Thuja occidentalis ‘Nigra’. Consider planting low-growing plants with bright yellow or chartreuse foliage near the base, such as certain Japanese forest grass varieties or creeping Jenny, to create a striking border effect against the hedge line. Deciduous shrubs that offer vibrant fall color, like burning bush or some dogwoods, also provide excellent seasonal contrast behind or adjacent to this evergreen structure.

Seasonal Care Calendar

Spring preparation involves checking the plant for winter damage; light pruning can correct minor broken branches before the flush of new growth begins. Water deeply and consistently as the weather warms, especially if the previous winter was dry, moving into the medium watering schedule. During the summer, monitor for pests like spider mites, particularly during dry spells. In autumn, ensure plants receive ample water before the ground freezes, which helps prevent winter desiccation and potential winter burn on your Thuja occidentalis ‘Nigra’.