March 2017
The Magic of Gardening

Trouble with your Leyland cypress?

Consider some alternative screen plants for your landscape.

 

A healthy Leyland cypress.

I have been around the horticulture world long enough to see once highly praised landscape plants become a curse word to both pathologist and horticulturist. Some of these has-beens include Chinese privet, Bradford pear, red tip photinia and, more recently, Leyland cypress.

Over the past 10 years or so, I have seen a great increase in the following question regarding this last plant and that is, "Why is my Leyland cypress turning brown?"

Leyland cypress became very popular as a screen plant because it is a relatively inexpensive, fast-growing, thick conifer. When I moved to my current home in 1998, this plant was being highly touted as the near-perfect, quick screen that was tough as nails. Too much praise should have been my tipoff to avoid this plant, but I planted a row of them to screen an unwanted view. I planted them at the recommended 12-feet-apart spacing that is probably twice as far apart as what I typically see in most home and commercial landscapes. It is not too unusual for me to see them as close as 4 feet apart. The close spacing is a big part of the problem. My hedge looked really good for about 10 years; then I started to see some limbs dying as the plants grew together. I knew by this time that they were susceptible to diseases and insect pests. I took out every other plant so they are now spaced 24 feet apart and within a few years they filled the space between very well and they are doing quite well. I have never treated them for any pest and have never given them supplemental water since the year after planting.

My personal experience tells me that they are in fact nice screen plants as long as they have well-drained, but not droughty, soil, and they are given adequate space to grow. Remember, these plants can get huge and are really too big for most residential situations as a screen. In my situation, where I have plenty of space, they serve the purpose I needed them for. A more appropriate use for landscape purposes would be as a specimen plant, but give it lots of elbow room because it can easily reach over 70 feet tall and 40 feet wide.

For those who have already planted a screen planting of Leyland cypress, you need to be aware of their most common problems. They are susceptible to fungal-incited canker and dieback diseases, including Seiridium canker and Botryosphaeria canker, not to mention bagworms, scale and mite problems that may become an issue.

Seiridium canker is becoming a serious problem for Leyland cypress. This disease may kill young shoots, older branches and, in some cases, entire trees. Bleeding cankers are often observed on the trunks of infected trees. Trees stressed by transplant shock, drought and/or high or low temperature may be more likely to be infected by this disease.

A Leyland cypress affected by seiridium canker.

 

Botryosphaeria canker is usually found on established Leyland cypress. Branch dieback is often the first symptom observed on diseased cypress. Again, bleeding cankers may be observed on the trunk of infected trees, but is much more common with Seiridium canker. This fungus, like many other fungi that cause cankers, is opportunistic and attacks plants weakened by drought stress, site problems, crowding, pruning wounds, insect damage or construction damage. Even though drought conditions can exacerbate this disease, the problem can also be worsened by poorly drained soils.

"These canker diseases have similar symptoms of scattered dead branches throughout the canopy," Dr. Jim Jacobi, Extension plant pathologist, said. "However, lately Botryosphaeria canker is the more common of the two canker diseases of established Leyland cypress. Last year’s late-season dry weather will likely greatly increase problems with canker diseases. Planting in good, well-drained soil, mulching and watering during dry weather are the key factors to growing healthy Leyland cypress, but proper spacing is also critical. Fungicides are of little help with these diseases."

For detailed information on diseases of Leyland Cypress, check out the Extension publication at this web address, http://www.aces.edu/go/670.

If you have not planted Leyland cypress already, you may want to consider some alternative screen plants. Some good screening plants for the Southeast include many hollies, viburnums, "Little Gem" magnolia, wax myrtle, Illicium, osmanthus, camellias, red cedar, Cryptomeria, columnar junipers and Thuja Green Giant Arborvitae. This last plant is often touted as a great substitute for Leyland cypress because it is similar in growth habit, appearance and size, but it can be planted too closely causing problems down the road as well. In general, all conifers need good air (space for air to flow all around) and soil drainage. Always check that the particular plant you choose is suited to the sun, soil and moisture conditions at your site, and that its ultimate size is acceptable.

What I usually encourage homeowners to do if space allows is to create a mixed shrub borders with a variety of different species. This practice can reduce the potential for diseases and insects becoming a severe problem, as can happen when only one plant is used. For best appearance in a mixed border, stagger odd-numbered groups of shrubs and trees with a variety of texture and shape, and plan for ultimate size when placing them. Plant tall plants toward the rear and come forward with successively smaller species.

 

Tony A. Glover is a County Extension Coordinator in Cullman County.