Eastern arborvitae (Thuja occidentalis), also called eastern white cedar, and its cultivars are among the most commonly planted. This native of eastern North America grows wild in moist woods. While the straight species can grow as tall as 40-60 feet, the more widely planted cultivars have more restrained growth habits and make better landscape plants. 'Nigra', also known as 'Dark American', is a popular selection that keeps its deep green color all winter long; it grows 10-20 feet tall and 4-6 feet wide at maturity. 'Smaragd', also called 'Emerald Green', is finer textured and slower growing, reaching 10-15 feet tall and 3-4 feet wide. Where space is limited, 'Holmstrup' is a good choice, growing about 10 feet tall and 3 feet wide. Not all cultivars are columnar. 'Woodwardii' makes a globe-shaped shrub 4-8 feet high and 5-10 feet wide. 'Little Giant' has a similar growth habit but gets only 2-4 feet tall and wide. 'Golden Globe', at 2-3 feet tall and wide, makes a great accent with its bright gold foliage. Most eastern arborvitae are hardy in zones 4-7.
The western native, giant arborvitae or western red cedar (Thuja plicata), is larger and faster growing than its eastern relation, but not as cold hardy, growing well in zones 5-7. One of the most common cultivars is 'Green Giant' which has a fast growth rate (up to 5 feet a year under good conditions) and is tolerant of drought. It reaches 30-50 feet tall and 12-20 feet wide.
Oriental arborvitae (Thuja orientalis, now more correctly Biota orientalis) is the least hardy, to zones 6-11, and is best adapted to the south and southwestern parts of the country. Growing 18-25 feet tall and 10-15 feet wide, it is useful for hedges and as a specimen. There are many cultivars available with varying growth habits.
Special features of arborvitaes
Good for hedges and screens
Choosing a site to grow arborvitaes
Arborvitae grows best in full sun, but will tolerate light shade. Giant arborvitae is the most shade tolerant. All prefer fertile, moist, well-drained soil.
Container grown plants and balled and burlapped plants can be set out throughout the growing season. Spacing will vary with the species and cultivar. Dig a hole only as deep as the root ball and 2 to 3 times as wide. If your soil is in very poor condition, amend the soil you've removed from the hole with a small amount of compost. Otherwise don't amend it at all. Carefully remove the tree from the container and set it in the hole. If you are planting a balled and burlapped plant, remove as much of the burlap as you can and snip off the wire basket if present. Fill in around the root ball with soil until the hole is about half filled. Then firm the soil and water thoroughly. Fill the hole with the remaining soil and water again. Form a raised ridge of soil around the outside edge of the hole so it acts like a berm to help hold in water. Spread mulch 2-3 inches deep over the root zone, but keep it several inches away from the trunk.
Give plants regular watering until well established, especially for the first growing season. When you water, be sure to put on enough water to soak the entire depth of the rootball, then let the top few inches of soil dry out before rewatering. Shear plants to shape and control size in early spring or early summer.