Leyland cypress (Cupressocyparis leylandii) is a fast-growing evergreen hybrid with soft, graceful foliage that was developed in Wales from trees in the Pacific Northwest. It is a favorite in many parts of the United Kingdom and in southeastern United States, although its popularity there may be on the decline because of its susceptibility to disease.
The Leyland cypress is a hybrid between the Monterey cypress (Cupressus macrocarpa) and the Nootka cypress (Chamaecyparis nootkatensis). The hybrid was developed in Wales in the 19th century and is unusual because it is a cross between species of different genera. The original hybrid, a cross between the male Monterey cypress and a female Nootka, has sage green foliage and is known as Haggerstown gray. A later cross between a female Monterey and a male Nootka produced a hybrid with rich green foliage called Leighton green.
Leyland cypress has small branches with blue-green or dark green foliage that is soft and feathery. The sprays of flattened, scaly leaves curve gracefully upward forming a handsome pyramid shape. It yields a small, brown cone.
The Leyland cypress sometimes produces seeds, which is unusual for a hybrid between two species. Propagation is normally by cuttings. Seedlings are available at many nurseries in the U.K. and southeastern U.S.
The attractive but rapid-growing Leyland cypress is often grown for windbreaks and screens. It can be pruned into hedges that require frequent trimming. Pruning a Leyland cypress for a hedge, screen or windbreak should not be done in wet weather to avoid diseases. Leyland cypresses are often sold for Christmas trees.
Leyland cypress trees grow faster and larger than many people expect, requiring frequent pruning to keep them away from power lines and from pushing into buildings. Untended Leyland cypress hedges are a special problem in the U.K. These trees have shallow roots, making them susceptible to being blown over by high winds. When they are planted too close together in poorly drained soil, they are subject to root rot and canker diseases.
Seiridium fungal canker is a common cause of twig dieback in Leyland cypress. It causes yellowing or browning of lateral or top branches. Infected bark cracks and oozes resin.
Botrysophaeria fungal canker causes branches or shoots of Leyland cypress to turn yellow or rust brown. The cankers can encircle and kill branches.
Two fungal root rot diseases commonly afflict Leyland cypress. Phytophthora root rot strikes young trees causing yellow foliage, stunted growth and often death. Annosum root rot, which kills larger roots, ordinarily strikes when nearby pine trees have been felled. The tree declines, turns yellow and ultimately dies.
Bagworms are also a problem with Leyland cypress.