Be wary of these five landscape trees
Saturday, July 21, 2018
Not all trees are created equal. While most trees that cover our landscapes provide us with aesthetic and ecological benefits, there are a few that probably do not belong here. Some trees can be invasive, some are insect and disease prone, and others may not grow well in our eastern North Carolina environment. I have come up with five trees that I will caution you to plant. As a disclaimer, I am not telling you what to plant or not plant. This article is based on research, observation and experience.
Bradford pear (Pyrus calleryana)
I know I am not the first one to raise an issue with Bradford pear trees, and I certainly won’t be the last. Back in March, Mark Rutledge wrote a column in The Daily Reflector titled “Celebrate National ‘Cut Down’ Your Neighbor’s Bradford Pear Week,” and it remains one of my favorite newspaper columns of the year by far. Though Mark has several humorous remarks throughout the column, he touches on several great points.
Bradford pear trees are a cultivated ornamental pear that originated in China. These trees have since cross-pollinated with native pear trees throughout the U.S., producing offspring at a rapid rate. A rate so rapid that these trees are considered invasive. The branches of Bradford pear trees are rather weak, and broken branches will only become more common as the tree matures.
These trees are also highly susceptible to a disease called fire blight. This disease is caused by a bacterium called Erwinia amylovora and causes branch tips to turn black, become brittle and curl into a “shepherd’s hook.” Once this disease has infected the tree, there is no irradicating it, and the tree will eventually die. Though there are chemicals that can be applied preventively, such as copper-based fungicides, they have mixed results at best. And I am sure if your nose has had the displeasure of smelling a Bradford pear flowering in the spring, you’ll have no interest in adding this tree to your landscape.
Japanese Zelkova (Zelkova serrata)
The Japanese Zelkova is a common alternative to the American elm due to its similar appearance and will provide a great addition to any landscape if planted in a proper location and given proper care. However, I have seen many Japanese Zelkova trees planted in parking lot islands or in compacted soils. These sites will stress the tree to the point of branch dieback.
Though this tree’s hardiness zone ranges from 5-8 (Pitt County is hardiness zone 8a), I believe some summer temperatures may be a little too hot for this tree because I have seen many trees exhibiting signs of heat stress.
My last concern with this tree is the growth of the lateral branches. Several lateral branches of the tree will attach to the main trunk at a sharp angle. This structure provides the “vase-shape” of the tree, but if the branches are not pruned, they tend to fail.
My only major concern with palm trees is the actual hardiness of the plant. Some palms are sold as “winter hardy,” such as the windmill palm and dwarf palmetto, but even those cannot withstand the temperatures we receive in the winter months. The past two winter seasons, I received many calls and samples of palms that had been damaged or died from the cold weather. The risk that you take with planting this tree in your landscape is replanting it every other spring.
Leyland cypress (Cuprocyparis X leylandii)
Diseases such as cankers and needle blight will kill off portions of the tree and can lead to an early death. The sheer amount of Leyland cypresses in the landscape has caused these deadly diseases to spread like wildfire, killing many trees. In addition to those diseases, an insect known as the bagworm feeds voraciously on the foliage of the Leyland cypress. Bagworms, whose cocoons are often mistaken for cones, have the ability to defoliate trees in a matter of weeks.
The manner in which Leyland cypress trees are planted can exacerbate this issue. Leyland cypresses are usually planted as a hedge or screen row. Being planted so closely together allows these already aggressive diseases and insects to spread even more rapidly. Though there are some control measure for cankers, needle blights and bagworms, they are rarely effective once the tree has been infected. I would not recommend planting this problem-prone tree in the landscape.
Mimosa (Albizia julibrissin)
If you’ve been in eastern North Carolina for only a split second this summer, you’ve probably witnessed the pink, feathery blossoms of a Mimosa tree. Though this tree has a pretty and unique flower, it is an ecological nightmare. Originally from China, mimosa trees are considered an invasive species. They can colonize entire areas with root sprouts and seeds that are spread via animals and water. Their seeds are viable for many years. This invasive is a strong competitor in open areas or forest edges due to its ability to grow in various soil types, its ability to produce large amounts of seed and its ability to resprout when cut back or damaged.
For more information on what trees may or may not fit well in your landscape, contact the Pitt County Master Gardeners at 902-1705. Thanks for reading!
Eric Derstine is the horticulture agent with the North Carolina Cooperative Extension Service-Pitt County. Contact him at firstname.lastname@example.org.