“Green Giant” arborvitae (Thuja “Green Giant”), hardy from U.S. Department of Agriculture plant hardiness zones 5 through 8, is a fast-growing, disease-resistant evergreen often recommended to replace the canker- and root rot-prone Leyland cypress (X Cuprocyparis leylandii). Although “Green Giant” might seem superior, it has drawbacks as well as advantages.
Green Giant Facts
Arborvitaes make handsome hedges. Their dense growth and sculptural foliage adapt well to both formal and informal landscapes. “Green Giant” is a hybrid (Thuja plicata x Thuja standishii) arborvitae that grows rapidly -- 3 to 4 feet per year under ideal conditions -- to a height of 40 to 60 feet. They are more disease-resistant than the Leyland cypress, which is hardy from USDA zone 6 through zone 10, and more deer-resistant than other Thuja varieties.
“Green Giant’s” hardiness range extends across temperate parts of the country -- on the Gulf Coast or in much of California, they are not as heat tolerant as the Leyland cypress. Although rated as damaged infrequently by deer, “Green Giant’s” soft leaves become more attractive when little else is available during winter, if it’s surrounded by plants seldom damaged -- or when deer are starving.
“Green Giant” makes a carefree hedge -- if you want a 30-foot-tall screen. A lower hedge requires work. Arborvitae, like other evergreens, loses old leaves from the inside of the tree outward as new growth begins each spring, so chopping back branches too energetically exposes inner branches, which remain bare after leaves brown and drop. “Green Giant” grows 3 to 4 feet annually, so it requires conservative sheering several times a season to keep it 5 to 10 feet tall. Ladders and special equipment might be needed to tame an undisciplined hedge. In addition, “Green Giants” grow 12 to 18 feet wide, so give them enough space to grow -- set plants 5 to 6 feet apart for a hedge.
“Green Giant” needs a giant place in the sun. The tree suffers when it is positioned in shade, under overhanging evergreens or against the wall of a tall building. Shading results in browning on the shaded side, uneven growth or a leaning tree in search of sunlight. This need for full sun means keeping areas around your hedge clear of plantings that might mature and shade parts of the hedge along its length, leading to uneven growth and brown patches.
Bagworms, named for the shaggy cocoons where they spend the winter, emerge as larvae from May to June and live on your ”Green Giant” all summer. Male bagworms become moths, but female bagworms return to the bags to lay more eggs in September and October. Bagworms have natural enemies -- predatory insects and birds -- and you can pick off the 1 1/2- to 2-inch bags. Insecticides are only effective on the larval caterpillars as they emerge from their bags in spring.