Oriental Arborvitae, Thuja orientalis (also known as Platycladus orientalis)

Summary:

Foliage: Flat scale-like foliage without a sweet fragrance when crushed; branches are held in a flat vertical plane; evergreen Height: About 20 feet Spread: About 15 feet

Shape: Large shrub or small tree with a variable habit ranging from round to oval to conical, to columnar; there are numerous cultivars that exhibit these forms Main features: Oriental arborvitae is generally an oval large shrub/small tree conifer species; cultivars and not the species are sold in garden centers. This species has a stately appearance and useful as a specimen plant (used alone as a focal point), accent plant, as a border planting, or anywhere an oval evergreen is appropriate. There is significant variation within the species. This variation is evident in view of the numerous cultivars (more than 40) that vary in size, form, and color. The species is typically slow-growing and quite tolerant of adverse conditions. Oriental arborvitae tolerates hot (zone 11), dry, alkaline, and moist soils, although growth will be especially slow under these conditions. In contrast to pines, arborvitaes hold their lower foliage with age.

There are two disadvantages of this species 1) the green foliage evident during the growing season goes off-color in winter, a yellow/brown-green, 2) plants are typically multi-stem which predisposes them to splitting apart in heavy snow. Cultivars will be described.

Plant Needs:

Zone: 6 to 11 Light: Full sun (will be less dense in part shade; will not tolerate shady sites)

Moisture: Average but will tolerate dry to moist soils

pH range: Acid to alkaline

Functions:

Oriental arborvitae’s oval form and retention low foliage at the base of the plant confers a formal appearance. Thus, it is suitable as a specimen plant, accent plant, as a border plant, or anywhere an oval evergreen species is appropriate.

Care:

Arborvitae has a relatively slow growth rate which can be an advantage, i.e., low pruning requirement, or a disadvantage, i.e., takes several years to grow to the desired height. This species is tolerant of pruning so once per year pruning can keep the plants at a desired size; one can even manage this species to form a medium sized hedge (less than 8 feet tall). When pruning, one must not remove all the foliage from any one branch. Since new buds are only produced on branches with new foliage, new growth will not emerge if one cuts off all the foliage on a branch. Plants are typically multi-stem which predisposes them to splitting apart in heavy snow.
 

Additional Information:

There are numerous cultivars that vary in size, form, and color. Some of the more popular cultivars in the trade are:

‘Blue Cone’ compact conical form with slightly blue foliage and blue cones

‘Compacta’ conical dense form

Yellow-foliage cultivars: ‘Aurea Nana’ (Berckman’s Golden Arborvitae) Ultimately a large shrub (15 feet) with bright yellow foliage in spring turning to yellow green in summer and winter; Other forms with yellow foliage: ‘Collen’s Gold’, Filliformis Aurea’, ‘Golden Ball’ ‘Westmont’ compact round dwarf form (to about 3 feet tall)