'Nigra' Arborvitae (Thuja occidentalis 'Nigra')

Plant Snapshot

Common Name: 'Nigra' Arborvitae
Latin Name: Thuja occidentalis 'Nigra'
Hardiness Zones: USDA zones 3–7
Typical Height: 8–15 ft (240–450 cm) at maturity for landscape specimens
Typical Spread: 3–6 ft (90–180 cm) for narrow forms used in screens
Bloom Period: Evergreen with inconspicuous pollen cones; not grown for flowering
Soil Preferences: Moist, well drained soil; tolerates clay and wet sites better than many conifers. Prefers slightly acidic to neutral pH. Poor drainage can cause root rot and decline.
Light Preferences: Full sun to partial shade. Best foliage color and density in full sun. Tolerates some shade but may thin.
Toxicity: Contains aromatic oils that can be toxic if ingested. May cause gastrointestinal upset and more serious signs in large ingestions. Confirm pet and livestock risks with poison control.
Propagation: Propagate by semi ripe or softwood cuttings to retain cultivar traits. Grafting is used commercially. Seed does not guarantee true to cultivar.

Key Facts

A dark foliaged cultivar of eastern arborvitae
Narrow to narrowly pyramidal evergreen habit
Valued for vertical screens and hedges
Prefers moist, well drained soil and regular moisture
Tolerates partial shade but performs best in full sun
Propagate by cuttings to retain cultivar traits
Not grown for showy flowers because it has inconspicuous cones
Contains aromatic oils that can cause poisoning if eaten in large amounts

‘Nigra’ Arborvitae (Thuja occidentalis ‘Nigra’) is a dark foliaged cultivar of eastern arborvitae with a narrow, narrowly pyramidal evergreen habit. It is used for tight vertical screens and hedges but needs regular moisture and can suffer where soils are either very dry or poorly drained.

Identification

‘Nigra’ shows dense, dark green to nearly black foliage on a narrow, upright crown. It is evergreen and not grown for showy flowers since it produces only small, inconspicuous pollen cones. Like other Thuja it contains aromatic oils that can cause illness if eaten and may irritate sensitive skin in some people.

Where to grow and best uses

Plant ‘Nigra’ where a slim, formal screen or hedge is needed. It performs best in full sun for color and density but tolerates partial shade with some thinning. Landscape specimens commonly reach about 8 to 15 feet tall with a 3 to 6 foot spread, making it suited to narrow garden spaces and property line plantings.

Planting and spacing

Space plants according to the desired screen density, often about 3 to 6 feet apart for a close hedge. Establish plants in sites with consistent moisture and good drainage so roots settle quickly. Timing for planting varies by climate but aim to establish roots before seasonal extremes to reduce transplant stress.

Water and soil

‘Nigra’ prefers moist, well drained soil and tolerates heavier or seasonally wet soils better than many other conifers. Regular moisture keeps foliage healthy and encourages steady growth. Extended waterlogging can cause root rot and decline while very dry conditions lead to browning and slowed growth.

Care and pruning

Light annual trimming maintains a neat narrow form and controls spread for screens. Size will respond to site fertility and irrigation so adjust pruning frequency to growth vigor. Avoid drastic pruning into old wood since recovery is slower from leafless stems; monitor trees for winter dieback in colder sites and replace or renovate as needed.

Propagation and commercial production

Maintain cultivar traits by using semi ripe or softwood cuttings or by grafting as done commercially. Seed does not reliably produce true to the ‘Nigra’ cultivar. Consult propagation manuals for timing and rooting techniques if you intend to strike cuttings.

Toxicity and safety

Thuja species contain volatile aromatic oils that can cause gastrointestinal upset or more serious signs if large amounts are ingested. Keep clippings and foliage away from livestock and pets and confirm specific risks with local poison control or extension services. Handle with care if you have sensitive skin.

Frequently asked questions

How fast does ‘Nigra’ Arborvitae grow?: Growth rate varies by site and care. In typical landscape conditions plants commonly reach roughly 8 to 15 feet over several years; wetter, fertile sites and irrigation speed growth while dry or cold sites slow it.
Is ‘Nigra’ Arborvitae safe for pets?: It contains essential oils that can be toxic if eaten. Small exposures may cause stomach upset. Check with poison control or a veterinarian for species specific advice.
How far apart should I plant them?: For a dense screen plan on roughly 3 to 6 feet between plants depending on the desired gap and the specific nursery clone’s spread.
Can ‘Nigra’ grow in shade?: It tolerates partial shade but achieves best foliage color and density in full sun. Deeper shade often leads to thinning within the hedge.
How is ‘Nigra’ propagated?: Propagate by semi ripe or softwood cuttings or by grafting to retain cultivar characteristics. Seed rarely produces true to type.