Trees for Urban Landscapes
By Mary Helen Ferguson, Extension Agent, Horticulture
Have you visited the Cooperative Extension/City of Asheboro Demonstration Garden on the corner of W. Walker Ave. and S. Church St. yet? As you may recall, I wrote in last month’s column about the plants in the evergreen screen part of the demonstration garden. This time, I’m going to focus on some of the trees.
Trees in urban sites, such as yards, landscapes around businesses, and highway right-of-ways, can experience stress to which trees in more natural areas are less likely to be subjected. Soil compaction (from foot traffic, vehicle traffic, etc.) and air pollution are a couple of examples of stressors that may affect urban trees.
Researchers from NC State University tested over one hundred types of trees to determine which were best for urban sites. We have the Autumn Blaze® maple (Acer x freemanii ‘Jeffersred’), one of those determined to be among the top ten, in our demonstration garden. The Autumn Blaze® maple is a cross between red maple (Acer rubrum) and silver maple (Acer saccharinum). It has very good fall color, grows quickly, and tolerates poorly drained soil. This maple can reach 50’ tall and 40’ wide, or larger. (Remember to consider the mature width when deciding if you have room for a tree and, if you do have room for it, how far it needs to be planted from the house, etc. Consider the height, also, especially if there is a power line overhead.)
While people may be more familiar with the native flowering dogwood, Cornus florida, the kousa dogwood (Cornus kousa) is considered more drought tolerant and generally more disease- and insect-resistant than the native species. It is a better choice for sites that get a lot of sunlight. The kousa dogwood is similar to the native flowering dogwood in appearance, but there are some differences: The bracts (what we often think of as the petals) are pointed on the end, instead of rounded and notched, and kousa dogwoods bloom later than C. florida. The kousa dogwood can be expected to grow to approximately 20’ to 30’ tall and wide.
Crabapples have qualities that make them desirable for urban sites, but be careful to choose a cultivar that is resistant to the diseases that affect some crabapples, including fire blight, cedar apple rust, and others. The ‘Prairifire’ crabapple (Malus ‘Prairifire’) that we have is one of the most disease-resistant crabapples. It has dark pink flowers and can be expected to grow to approximately 20’ tall and wide. While we don’t have it in our garden, ‘Callaway’ is a disease-resistant white-flowered crabapple that grows to about 15’ to 25’ tall and wide. (For more information on the disease-resistance of crabapple cultivars, see https://www.ces.ncsu.edu/depts/hort/hil/hil-8613.html.)
While it’s not typically thought of as a tree, I also want to mention our ‘Blush’ loropetalums (Loropetalum chinense var. rubrum ‘Blush’). Loropetalums, or Chinese fringe-flowers, have become popular, as they have few problems and, depending on what cultivar is chosen, can function as either a green- or purple-leaved screening plant. They also have dainty white or pink (again, depending on the cultivar) flowers in the spring. However, like many plants, they’re often not given enough room to grow without regular pruning.
I was inspired when I was in Savannah, Georgia, earlier this year and saw loropetalums trained to grow as multi-stemmed trees, like crepe myrtles often are. I think this is a great use for this plant. A loropetalum could be trained this way when something that looks like a tree is desired but there isn’t room for a larger tree (e.g., if a power line is overhead or if the site is close to the house). You could also train a loropetalum in this way if you want a purple-leaved small tree without the disease and insect issues of the purple leaf plum or the cost, leaf spots, and leaf scorch associated with Japanese maples. Of course, loropetalums have the additional advantage of keeping leaves year-round, if that is something you desire. Having written all this about growing loropetalums in a tree form, if you come to our garden, be aware that ours are currently growing as shrubs.
‘Blush’ loropetalum can be expected to grow to approximately 4’ to 8’ tall and wide. ‘Ruby’ is another compact purple-leaved loropetalum but has been found from time to time to suffer from something called loropetalum decline. ‘Burgundy’, another popular cultivar, grows to approximately 6’ to 10’ tall and wide. There are a number of other purple- and green-leaved cultivars available.
You’re welcome to stop by the demonstration garden and take a look at these plants. To read more about trees for urban sites, see the following links:
For more information about specific plants, you can go to www.ces.ncsu.edu. I can be reached at 336-318-6000.