The Heartbreaking Leyland Cypress: What You Need to Know

The Leyland Cypress (Cupressocyparis leylandii) was developed in England in 1888. The tree is a hybrid of the Monterey Cypress (Cupressus macrocarpa) and the Alaska or Nootka Cypress (Cupressus nootkatensis). The natural range of these 2 native North American plants is separated by 400 miles, but both plants were growing in close proximity at the Leighton Hall Estate, at one time owned by a Liverpool banker by name of Christopher Leyland. The genus Cupressocyparis arises from some controversy over the generic origin of the Nootka Cypress as some taxonomists classify it under the genus Chamaecyparis. That would imply that the Leyland Cypress is bigeneric cross, a very rare occurrence in conifers.

The modern popularity and widespread use of the plant began in the 1950’s, and by the 1980’s use of the Leyland Cypress was widespread. It is fast-growing, evergreen, strikingly beautiful in form and color, and adaptable to many situations. Like so many plants introduced before and since that are touted as the “perfect landscape plant,” the Leyland Cypress has fallen from grace. In the 1960’s, that perfect plant was the Red Tip Photinia. In the 1970’s, it was the Bradford Pear. So the Leyland Cypress was planted – everywhere! For decades it became one of the go-to plants for hedges, screens and specimens, and is still planted for these purposes. Despite the fact that the tree can grow 20 feet wide and 70-100 feet tall, many became hedges with a planted spacing of 5 feet or less. The trees grow quickly and provide privacy for individual homes on increasingly smaller lots.

Then the problems started. Being a cone-bearing plant with a Mediterranean cross Northern Temperate Cloud Forest heritage,the Leyland Cypress prefers moderate temperatures and soils that are airy and drain quickly, and on the moist side but never saturated and never bone-dry. Georgia conditions are precisely counter to this. Our air is damp with humidity, our high clay-content soils hold water, drain poorly, and exclude oxygen from the pore spaces in the soil. Not only that, while Georgia normally gets a robust 48-52 inches of rainfall per year, the distribution is anything but even: during the late summer and fall of 2016, we went well over 3 months with no rainfall whatsoever. Conversely, as of September 30, 2018 we have had 46.18 inches of rainfall – nearly 8 inches above average for this time of year. These contrary conditions and vast swings in soil moisture, coupled with the fact that the plant’s popularity has rendered it nearly a monoculture in close urban plantings, has made these plants susceptible to disease issues. Add to this the specter of broken branches from winter ice and summer thunderstorms, the diseases can spread rapidly.

There are 2 primary fungal pathogens that attack Leyland Cypress trees in the Southeast, Seiridium Canker and Botryosphaera (Bot) Canker. The symptoms of both of these fungal pathogens are the yellowing or browning of the foliage on one or many of the top or lateral branches. This telltale “dieback” is what we have all become so painfully familiar with. A closer look at the branches and main stem may reveal beads or runny areas of amber-colored sap oozing from the wood (Seiridium) or cankers, sunken areas girdling the base of dead shoots or branches (Bot canker). Unfortunately, there are no effective chemical treatments for the management of these diseases. While the spread of these fungi cannot be stopped, it can be slowed through some of the following management practices:

Planning & Planting

• When considering hedges and screens, think about using a variety of plants as opposed to a monocultural planting of Leyland Cypress trees or other conifers (yes, these diseases and issues are associated with other conifers such as Italian Cypress). When screening unpleasant views, a single plant is often all that is needed. A solitary Leyland Cypress has a much better chance of growing with a minimum of problems due to better light, air movement, and lack of similar plants in close proximity.
• Thoroughly amend the soil when planting to improve our common clay soil. Leyland Cypress trees are shallow rooted. Positive drainage is a must! Downey Trees has several products to improve drainage and poor soils.
• Provide adequate spacing between plants. Given the fact that the trees can grow 10-20 feet wide, planting them too close is a recipe for disaster!
• Provide plenty of water during the establishment period of new plants, and develop a plan to provide supplemental water during dry periods. It is a common misconception that conifers such as Leyland Cypress trees are tolerant of extreme drought. This is not the case!

Management of Existing Trees

• Avoid over-fertilization of plants – This often produces lush growth that is more susceptible to disease.
• Facilitate watering during dry periods – There is not much that can be done for established plants when we receive too much rain, but the wild wet/dry fluctuations of natural rainfall predispose Leyland Cypress to disease. Try to manage water to 1 inch per week (natural rainfall plus supplemental watering).
• Prune dead branches (either those shaded or those diseased) and sterilize pruning tools between cuts. Here are three ways to do this:
  • A 10% chlorine bleach solution (1 cup bleach to 9 cups water). Note that chlorine bleach can corrode pruning tools.
  • Full-strength Lysol – This seems to be the preferred method for maximum sterilization with minimum corrosion.
  • Alcohol wipes – No drying required and may be a bit less cumbersome in the field.
• In situations where the height of the screening plants is valued, such as the case of the second-story deck in the photograph, it may be acceptable for the plants in a screening row to be more open at the base through elevation of the lower branches. Anything that can be done to promote light penetration and air movement within the canopy can prolong the life and health of the trees.
• Soil decompaction and sub-surface nutrient injections – Downey Trees can provide these two services to help maintain the health of existing Leyland Cypress trees or help slow the spread of Seiridium and Bot Canker in trees that are diseased.  De-compaction aids water penetration during dry periods and drainage during wetter times.  Nutrients enhance plant health by improving the living soil web as opposed to adding a high level of growth-stimulating fertilizers.
• Other diseases such as Cercospora needle blight also adversely affect the health and appearance of the trees. The photo showing Leyland Cypress Trees with browning foliage at the base of the plants is representative of Cercospora.  While fungicides are effective against some of these other pathogens, repeated applications are often needed, and failure to apply the other management practices often results in a recurrence of the disease.
• The best expectation from enhanced management of Leyland Cypress utilizing the suggestions above is a slowing of the progression of Seiridium and Bot Canker: management, not control, is the ultimate goal.

Thinking long-term, plan to replace Leyland Cypress trees with something else, perhaps even a diverse selection of evergreens. A possible exception to this may be that situation described above where one plant would satisfy the screening needs for a particular view. A single plant located in such a situation may receive the light, air movement, and isolation needed to provide a healthy growing situation, provided the other needs outlined above are met as well. Avoiding the past history of cultural mistakes with Leyland Cypress and other conifers may help you avoid the heartbreak that has become so commonly associated with this tree. Refer to the links below for additional information:

• https://secure.caes.uga.edu/extension/publications/files/pdf/B%201229_4.PDF
• https://en.wikipedia.org/wiki/Leyland_cypress
• https://s3.wp.wsu.edu/uploads/sites/403/2015/03/cloroxed-clippers.pdf

Descriptions of the above photos, starting with the top row and moving left to right:

1. Brown die-back in the branches shows the beginning of the development of disease in these Leyland Cypress trees.
2. Even though the lower limbs of these trees may be thinning form shade-out and disease, the upper portions of the trees still provide privacy for this second-story deck. Plant Health Care to slow the advance of the disease may be a worthwhile investment in such situations.
3. Amber-colored sap oozing from the branches and trunks is indicative of Seiridium Canker.
4. These Leyland Cypress trees have Cercospora – another disease of Leyland Cypress.
5. A close look at this Italian Cypress tree shows the same type of die-back, likely Seiridium.
6. An example of advanced decline in a stand of Leyland Cypress.