× Cuprocyparis leylandii – (Syn. × Cupressocyparis leylandii)
A hybrid between Monterey and Nootka cypresses.
There are a number of clones used in horticulture, particularly for hedging. The clone ‘Leighton Green’ has been the most widely used in forestry trials in Britain.
Leyland cypress is cold hardy throughout Britain, is not frost sensitive and shows very rapid early growth on a wide range of soils of poor to medium fertility. It is not suited to peats or soils of very poor nutrient status, but appears to grow on alkaline soils. The rapid early growth and moderate tolerance of exposure explains its popularity for hedging, but it is not suited to exposed upland sites, where it is also prone to snow breakage. It is probably best suited to more sheltered sites in western and southern Britain with >800 mm rainfall.
Pests and pathogens
Seiridium canker (Coryneum cardinale) causes scattered twig and branch death on affected trees. Cypress aphid (Cinara cupressivora) also causes similar symptoms of foliage browning, although the causal agent is very different.
Leyland cypress is also considered highly susceptible to Armillaria root rot (honey fungus) and Phytophthora root rot (particularly P. cinnamomi). Infection by either pathogen can lead to severe dieback or death.
The timber is naturally semi-durable. This is a species which could find an expanded role with climate warming, particularly in western Britain and on other sites with adequate soil moisture.