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Conifers/Question about Leyland Cypress


Hi Jim,
I have a question in regards to Leyland cypresses.  We just had some landscaping work done and we had 7 five foot Leylandís installed along a fence for some privacy.  I was first thinking about putting in smaragd arborvitaes as they only get 15í max I think.  It is also a narrower part of the property so I didnít want anything detruding.  I was also looking for something low maintenance but the arborvitaes I all saw all basically had double leaders and I donít know if thereís any way of training them to develop only a single leader.

Anyways, the owner from the nursery convinced me to get the Leylandís because they will grow faster than the arborvitaes.  I expressed concerns about them getting too big, but he said that as long as I trim them every spring I should be able to maintain them.  He said that I would have to train them by cutting the sides so that way they will fill out and not look leggy.  

My question is if I trim the sides every spring and top off the top of the Leyland (heading the Leyland I believe itís called) at the desired height can I keep it at tree form?  Current they are spaced 4 Ĺ apart.  Was having them plant them a future nightmare?

In my mind a tree form is conical or the top pointed. Leyland will grow at maturity about 40 feet tall and 8- 12 feet wide. Planted 41/2 feet apart they will grow together on the sides. IF you top the trees you can make a hedge out of them but will not have the tree form. I would leave them as is right now and over time you can prune back the sides if they grow too far out into the lawn. Beware that Leyland will get a couple of serious canker diseases but these can be treated as they show up.

Leyland cypress trees are subject to a couple of canker type diseases that effect the foliage.

Seiridium canker is probably the most important and destructive disease on Leyland cypress in the landscape. Although the fungi Seiridium cardinale, Seiridium unicorne, and Seiridium cupressi have been reported to cause disease on Leyland cypress and other needled evergreens, only Seiridium unicorne is most commonly associated with cankers and twig dieback on Leyland cypress.

One of the most noticeable symptoms of Seiridium canker is yellowing or browning of the foliage on one or more top or lateral branches. The discoloration is most likely to appear in early spring; however, it can be seen at any time of the year. The disease expansion often continues until a significant portion of the tree is destroyed. Upon closer examination, formation of numerous thin, elongated cankers is observed on stems, branches and branch axils. These cankers cause twig and branch dieback. Most of the cankers are slightly sunken, with raised margins, and they may be discolored dark brown to purple. Cracked bark in infected areas is often accompanied by extensive resin exudates that flow down the diseased branches. The cambial tissue beneath oozing sites is discolored with a reddish to brown color.

To minimize water loss and water competition with other plant species such as turf, mulch an area several feet beyond the lowest limbs. During hot, dry summer days, irrigate trees thoroughly around the base of the tree every 7-14 days, depending on soil composition. Take special care for trees located near drive-ways, paved areas or heat-reflecting buildings. Providing adequate irrigation during periods of drought is the best defense against Seiridium canker disease. Do not over water.

Sanitation, such as removal of cankered twigs and branches, helps prevent disease spread. Destroy pruned materials, and disinfect pruning tools by rinsing in rubbing alcohol or a solution of 1 part bleach to 9 parts water. Remove extensively damaged trees or trees that are damaged in the main trunk.

No cultivars or selections are known to be resistant to the disease. In the landscape, fungicides are seldom used and they provide no control once an infection has taken place.

Another damaging disease on Leyland cypress in landscapes is a canker and dieback named Botryosphaeria (Bot) canker, caused by the fungus Botryosphaeria dothidea. This aggressive disease affects a number of woody shrubs and trees worldwide, and it has been reported on azaleas, rhododendrons, flowering dogwoods and redbuds, among others. Plants suffering from environmental stresses (freezing, drought, or heat) or wounds are particularly susceptible to B. dothidea infection in landscape plantings.

In the landscape, Bot canker symptoms resemble those caused by Seiridium canker. Bright, rust-colored branches and yellowing or browning of shoots or branches are the first observed symptoms. Closer inspection reveals the presence of sunken, girdling cankers at the base of the dead shoot or branch. Sometimes, the main trunk shows cankers that might extend for a foot or more in length. These cankers rarely girdle the trunk, but they will kill branches that may be encompassed by the canker as it grows.

Canker surfaces may be cracked and have a darker color than the surrounding healthy bark. The discoloration often extends several inches below the canker periphery. Little or no resin "oozing" is produced on the infected areas.

To minimize water loss and water competition, mulch an area several feet beyond the lowest limbs. Removal of diseased twigs and branches helps prevent disease spread. Remove and destroy pruned material and disinfect pruning tools. Remove extensively damaged trees. In the landscape, no fungicides are recommended to control Bot canker.

I would enjoy them since you have them planted and IF they get cankers and the diseases gets to a point that the foliage is declining then you can replace them. This may or may not even happen.  


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Jim Hyland


Registered Forester in the Southern US with 30 years experiance in managing pines. Expert in pine forest health from management to control of pests to ID of species.

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