Leyland Cypress, X Cupressocyparis leylandi, was thought to be the plant world’s equivalent of a mule. Its parents are the Monterey Cypress ( Cupressus macrocarpa) and the Alaskan Cypress (of the genus Chamaecyparis, Xanthocyparis, or others depending on who’s looking at its DNA). Like many organisms, the Leylands exhibit “hybrid vigor,” and their growth rate can be remarkable – up to three feet a year.
Interestingly, the parents of the Leyland Cypress never had the opportunity to interbreed in nature, as they grew hundreds of miles apart – the Monterey Cypress being native to the central California coast (they are the wonderfully wind-sculptured trees in those calendar photos), and the Alaskan, or Nootka, Cypress from Alaska to Washington. In 1847, John Naylor inherited Leighton Hall in the British Isles from his uncle, Christopher Leyland. Naylor employed Edward Kempt to design the gardens with plants imported across the continents, including the U.S. West Coast parents listed above. Those cool, damp Wales springs encouraged cohabitation and sterile seedlings were found in 1888. The mother, in this first cross, was the Alaskan Cypress, fertilized by that California surfer from Monterey. In subsequent fertilizations, the roles of mother and father were occasionally switched.
Nearly two dozen different offspring have been named, and each and every one must be vegetatively propagated, as they are all sterile hybrids, ranging in color and form from golden and compact to deep green and towering. The favored child is “ Leighton Green,” which can reach 100 feet in 60 years, according to Southern plant guru Michael Dirr. Combine that with ease of propagation (you can buy them cheaply), resistance to salt spray (remember that parent on the cliffs overlooking the Pacific Ocean), and tolerance of different soil types, and this tree is the equivalent of a release by Beyonce.
Unfortunately, we’ve been in a drought cycle and the forebearers of the Leyland grow where summers are moist and cool. The shallow-rooted Leylands have suffered terribly, especially when they’re growing without irrigation. Their lush green foliage is often marred by brown, dying branches and tips caused by Seiridium and Boytryosphaeria fungi. Sadly, no effective spray exists, and if it did, it would be impossible for homeowners to apply to huge trees.
Control consists of keeping trees as healthy as possible. You can prune infected branches, cutting several inches below the problem area. Wipe your tools with alcohol or a 10 percent bleach solution between cuts. Keep several inches of mulch over the root zone, and water from below to avoid having wet foliage, as there is another fungal disease that often affects the lower needles if they are wet by a sprinkler.
Sadly, there is nothing you can do about our torrid summers. Unlike the workhorse mules, Leyland Cypresses do not have increased tolerance for stress, and their lifespan is severely shortened here. Clemson no longer recommends planting them, and the suggested replacement, Thuja “ Green Giant,” now is succumbing to the same diseases.
In the United Kingdom, the cooler summers allow these trees to reach their full glory. Gardeners were dismayed when their sunny rose gardens became engulfed in darkness from their neighbors’ rapidly growing Leyland hedges. Now there is an aspect of the Anti-Social Behavior Act that addresses this issue, and it is trim or be fined. I don’t think we are going to need that legislation in South Carolina.
Amanda McNulty is an associate extension agent for the Clemson University Cooperative Extension Service and is a co-host of “Making It Grow” broadcast weekly on ETV television stations. To reach her, email firstname.lastname@example.org