The previous owners of our home planted Leyland Cypress at the property line. The trees have grown very high. The neighbors have asked us to trim these trees in a “hedge-like” fashion, which means that we would need to cut the tops of the trees. One neighbor, who is a landscaper, insists this will not damage the trees. But several arborists have advised not to “top” the trees. We are willing to have the trees topped as long as this will not compromise the health of the trees.
Pruning Leyland Cypress (x Cupressocyparis leylandii) to look like a hedge can be a challenge.
Topping is not a recommended method for controlling trees, because it often causes them to grow faster (unless they are topped mortally) and thus must be done repeatedly and expensively, and also because it weakens the tree, which may cause it to drop limbs, rot, or blow over more easily. The group Plant Amnesty has a great deal of information about why one should avoid topping.
However, topping may be less harmful for x Cupressocyparis leylandii than for other plants, but it is still not a particularly effective solution. The University of Florida Extension concurs that this practice is less harmful
to x Cupressocyparis leylandii than it is to other species, but they still do not recommend it.
Peter McHoy’s A Practical Guide to Pruning (New York: Abbeville Press Publishers, 1993) also advises avoiding topping, but also notes that if one must top an x Cupressocyparis leylandii, it should be done in midsummer and repeated every few years.
However, in general, it would appear that topping is very much a last resort.
One book, Practical Tree Management: An Arborist’s Handbook, by T. Lawrence, P. Norquay, and K. Liffman (Melbourne: Inkata Press, 1993), recommends that “Where a tree requires severe reduction or radical alteration
of its aesthetically pleasing, natural growth habit, it is usually far better to consider replacing the tree with a species more suitable for the situation…” Thus, you may consider an initial pruning and eventual replacement.