deciding to cut down leyland trees
we have 8 leyland trees about 25 years old turning brown about 50 percent brown but provide great screening from neighbors and the birds love them but we dont want them to fall and damage our deck how do we know if they are in immediate danger of falling or if they can last a few more years?
Howard County Maryland
A cross between two Pacific coast species, the Leyland cypress thrives best in moist, cool climates with moderate temperatures. These trees are hardy to zone 6, however they don’t tolerate sudden temperature fluctuations. We indeed experienced some of these very cold sudden temperature fluctuations this past December and January. The first winter damage symptoms showed up as browning and dieback this spring as temperature begin to warm and stimulate new growth.
Since Leyland’s are often used for screening and wind breaks they are frequently exposed to temperature extremes and windy conditions that lead to drying out and cold damage.
One of the weakness of Leyland’s are their shallow root systems which makes them susceptible to stress through desiccation. Another weakness is the dieback and death of the water conducting tissue and cambium layer just under the bark during extreme winter temperature fluctuations.
There is no actual treatment for winter damage on Leyland cypress. Before pruning, allow the damaged tree to begin new spring growth. Often, if the damage did not injure the branch, new growth will emerge, and the browned needles will drop off naturally. If new growth does not emerge, the branch was severely damaged and should be pruned above where green color is still visible. Leyland cypress trees are tolerant of heavy pruning, but if more than one-third of the tree is damaged, the tree may need to be replaced.
If your browned areas put out new growth, the trees may be fine. If entire large branches are completely dead, and add up to 50 % of the tree, as you said, the trees may become unstable and a hazard. Here is a list explaining when to remove trees: http://extension.umd.edu/learn/how-do-you-decide-when-remove-tree
Winter cold injury can often lead to greater infections from a few common fungal diseases that affect foliage, stems, and branches such as Seiridium and Botryosphaeria cankers, as well as Cercospora needle blight. You can search these on our website if you're interested.
It's always best to diversify evergreen borders with a variety of evergreens and deciduous plant selections rather than just one species.