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Thuja occidentalis

American arborvitae

Cupressaceae

Eastern and central Canada and the northeastern United States

Fragrant (light)Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterMedium

HardinessZones 2–7

Overview

Thuja occidentalis is an evergreen conifer reaching 40-60 feet (12-18 m) tall and 10-15 feet (3-4.5 m) wide in cultivation, holding a narrow conical crown with branches to ground level in open positions. Foliage is carried in flattened sprays of overlapping scale leaves 0.1-0.2 inch (3-5 mm) long, yellow-green to mid-green above and paler beneath, releasing a resinous scent when crushed. Foliage turns bronze-brown between November and March in zones 2-5 and regreens in April. Bark is reddish-brown and fibrous, peeling in narrow vertical strips on trunks over 4 inches (10 cm) across. Cones are oblong, 0.3-0.5 inch (8-13 mm) long, with 4-6 pairs of scales, green ripening brown in September and holding a further year. Growth runs 12-18 inches (30-45 cm) per year on moist soil and 4-8 inches (10-20 cm) on dry ground. Deer browse the foliage to a clear line 5-6 feet (1.5-1.8 m) above ground in areas of high population, and multi-stemmed plants splay apart under wet snow, with stems breaking at the base. Trees on the cliff faces of the Niagara Escarpment have been dated at over 1,000 years old.

Native Range

Native to eastern and central Canada from Manitoba to Nova Scotia and to the northeastern United States south to Minnesota, Illinois, and Ohio, with scattered populations in the Appalachian Mountains of North Carolina and Tennessee. Grows in cool swamps, on stream banks, and on limestone cliffs and outcrops from sea level to 3,000 feet (900 m). Soils across the range run neutral to alkaline and are often shallow over rock.

Suggested Uses

Planted as a screen or hedge at 3-4 foot (0.9-1.2 m) spacing, as a specimen at 12-15 foot (3.7-4.5 m) spacing, and in shelterbelt rows on cold exposed sites. Heavy deer browsing restricts its use in rural plantings where deer are present. Grows in containers of 15 gallons (57 L) or larger for 4-6 years before root volume limits growth.

How to Identify

Foliage forms flat sprays of scale leaves carrying a raised resin gland on the outer surface, and crushed sprays smell resinous rather than of gin, which separates Thuja spp. from Juniperus spp.. Cones are oblong, 0.3-0.5 inch (8-13 mm) long, with overlapping woody scales, whereas J. virginiana carries blue berry-like cones. The underside of each spray is pale yellow-green without the white stomatal markings of T. plicata, whose sprays are also glossier and 2-3 times larger.

Appearance

Size & Dimensions

Height40' - 60'

Width/Spread10' - 15'

Reaches mature size in approximately 30 years

Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Pollen cones 0.1 inch (2-3 mm) long open at shoot tips in April and May and shed pollen over 7-14 days. Seed cones are green from May, ripen brown in September, and split to release winged seeds 0.2 inch (4-5 mm) long through October. Cone crops vary, with heavy years at 2-5 year intervals. Trees begin coning at 15-20 years of age.

Detailed Descriptions

Foliage Description

Yellow-green to mid-green, bronzing in winter

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 8.0(Neutral)

357912

Soil Types

loam clay chalk silt

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

20-30 years

Care & Maintenance

Care Guide

Water weekly through the first three seasons and during droughts longer than 3 weeks thereafter; foliage browns from the interior outward within 10-14 days of the soil drying and does not regreen. Roots are shallow and spread 1.5-2 times the branch width, so the root zone is mulched 2-3 inches (5-8 cm) deep and left unbroken by cultivation. Soil from pH 6.0 to 8.0 is tolerated, including shallow ground over limestone. Deer strip foliage to 5-6 feet (1.5-1.8 m) above ground between November and March where populations are high, and repeated browsing kills small plants. Bagworm larvae build spindle-shaped cases 1-2 inches (2.5-5 cm) long on the foliage from June and defoliate branches, while spider mites bronze the foliage in hot dry summers. Multi-stemmed plants are strapped together at 6-8 feet (1.8-2.4 m) above ground where wet snow loads split the crown.

Pruning

Shearing in late spring and again in midsummer holds hedges to a set width, with cuts confined to green foliage, since branches cut into bare brown wood produce no regrowth. Plants left unsheared build a conical crown 10-15 feet (3-4.5 m) wide over 20-30 years. Cutting the leading shoot stops height increase and produces multiple competing leaders 12-24 inches (30-60 cm) below the cut.

Pruning Schedule

late springsummer