(News article for August 13, 2022)
Since fall is a good time to plant most types of trees and shrubs, some of you may be starting to think more about landscape plans. The phrase “right plant, right place” encompasses much of what people need to know about landscaping. Plants should be well-suited to our climate, including our temperatures and the amount of rainfall that we get. We also need to appropriately match plants to the conditions of particular sites.
One way to get an idea of whether a plant is suited to the temperatures that we experience is to look at the hardiness zones for which the plant’s recommended. US Department of Agriculture (USDA) Plant Hardiness Zones are based on average minimum temperatures. Most of Tangipahoa and Washington Parishes are in zone 8B, while the very southern part of Tangipahoa Parish (roughly the area south of I-12) is in zone 9A. If a plant that’s only hardy in zones 9 to 11 is planted in zone 8, for example, it’s likely to eventually be killed by the cold.
While USDA Hardiness Zones are based on minimum temperatures, they’re often used to indicate the heat tolerance of a plant, too. So, if a reliable source of information says that a plant is hardy in zones 5 through 7, that plant probably won’t take our heat very well.
Information about what hardiness zones a plant is suited to is often available on plant tags, in books, and on websites about plants. OnlinePlantGuide.com, which has information put together by a couple of now-retired LSU professors, is a good source of information about the growing requirements of many landscape plants.
Site conditions to consider include the amount of sun or shade an area gets, how well drained it is, and whether the site gets more or less effective rainfall than the open yard.
Ornamental plants vary widely with respect to the amount of sun or shade to which they’re best suited. Azaleas typically perform better in sites where they get morning sun or partial shade rather than full sun. On the other hand, some flowering plants suited to full sun will not flower well if they are planted in a site that is too shady.
There are several things that affect how wet a site is, including the slope of the land, the soil texture (how sandy, silty, or clayey it is), and the depth of the water table. As with light needs, plants vary with regard to how wet or dry they “like” it.
While many plants need good drainage, there are a number that thrive in wet sites. River birch, buttonbush, Virginia sweetspire, and American beautyberry are just a few plants that tolerate wet conditions.
Be aware that plants placed near eaves of houses can get much more water than plants in the open yard. If you don’t have gutters, be careful about placing plants that are sensitive to wet feet near the edge of the house.
Finally, the expected mature size of a plant should be considered. Plants are often planted so that they look good when installed but eventually grow into each other or up against a building, unless they’re pruned regularly.
Some work can be avoided by choosing plants that, when mature, will fit the space in which they’re planted. If a shrub is expected to reach 8 feet wide, for example, it’s a good idea to plant it at least 5 feet from a house (half the mature width, plus 1 foot for air movement and access around the house).
Likewise, if there are windows that you don’t want blocked or overhead power lines nearby, consider how tall the plant will get.
Let me know if you have questions.
Contact Mary Helen Ferguson.
The bigleaf or "French" (actually native to Asia) hydrangea in the foreground and the oakleaf hydrangea and Japanese maple in the background are all plants that, in Louisiana, tend to perform best on sites with some shade. (Photo by M.H. Ferguson)