Thuja Green Giant Hybrid Arborvitae is a hybrid-cross between (Thuja standishii x plicata)

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Back in the mid-nineties when Thuja Green Giant started gaining popularly, most nurseries did not have any big trees to take their cuttings from. The western red cedar had been around for years and it is my theory that thousands of cuttings were taken from Western Red Cedar trees and sold as Thuja Green Giant. This is just my theory, not a comprisery theory, I would not name names if I had any.

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At Thuja Gardens we are still taking our cuttings from the trees we planted in 1999, they came from a big propagation nursery in Georgia. Today the Thuja Green Giants we planted in 1999 are only 8 feet wide x 30 feet tall, no way they are going to grow 30 more feet.

I still stand by the fact: Thuja Green Giant trees purchased from Thuja Gardens will grow 6 to 8 feet wide x 25 to 35 feet tall.

Thuja Plicata

Common Name: western red cedar

Type: Needled evergreen

Family: Cupressaceae

Native Range: Western N. America

Zone: 5 to 7

Height: 50.00 to 70.00 feet

Spread: 15.00 to 25.00 feet

Bloom Time: Non-flowering

Bloom Description: Non-flowering

Sun: Full sun to part shade

Water: Medium

Maintenance: Medium

Suggested Use: Hedge, Rain Garden

Leaf: Fragrant, Evergreen

Tolerate: Clay Soil, Black Walnut

Thuja Standishii

Common Name: Japanese arborvitae

Type: Needled evergreen

Family: Cupressaceae

Native Range: Central Japan

Zone: 5 to 7

Height: 20.00 to 30.00 feet

Spread: 10.00 to 15.00 feet

Bloom Time: Non-flowering

Bloom Description: Non-flowering

Sun: Full sun to part shade

Water: Medium

Maintenance: Low

Leaf: Fragrant, Evergreen

Other: Winter Interest

Tolerate: Black Walnut

If you look at the description (above) it looks as if Thuja Green Giant might have  inherited it's mature height x width more from it's japanese parent  thuja standishii.

Thuja Plicata

Culture

Best grown in moist, fertile, well-drained soils in full sun to part shade. Thrives in cool summer climates. Intolerant of dry conditions. Best in full sun, but generally appreciates some light afternoon shade in hot summer climates. It may struggle in the St. Louis area which has considerable different climate and soil conditions than the native habitat of this conifer.

Noteworthy Characteristics

Thuja plicata, commonly called western red cedar or giant red cedar, is native to the Pacific Northwest where it is typically found in cool but moist forest areas and bottomlands from southern Alaska along the Pacific coast to northern California and in the northern Rockies from British Columbia to Montana. This is the largest tree in the cypress family, growing in its native habitat to 100-200’ tall and living from 400 to 1000+ years. It features horizontal branching with sprays of scale-like dark green foliage that is aromatic when crushed. Fibrous, aromatic, reddish-brown bark. Small, upright, light brown seed cones (to 1/2” long).

Thuja Standishii

Culture

Grow in average, medium moisture, well-drained soils in full sun to part shade. Prefers moist, neutral to alkaline, well-drained loams. Intolerant of dry conditions. Best in full sun, but generally appreciates some light afternoon shade in hot summer climates such as the St. Louis area. Avoid full shade where foliage density will substantially decrease.

Noteworthy Characteristics

Thuja standishii, commonly called Japanese arborvitae, is a small to medium evergreen conifer that is native to subalpine forests on the Japanese islands of Honshu and Shikoku. In cultivation, it typically grows to 20-30' tall with a broad-pyramidal crown, slender trunk, fibrous reddish-brown bark and aromatic (lemony) scale-like leaves in flattened sprays. Leaves are bright green above and glaucous beneath. 

Western Red Cedar

(Thuja Plicata)

When Old

Western Red Cedar

(Thuja Plicata)

When Young

I have no use for a tree that will one day take my yard from me, my kids, or grandkids?