Richard Bogren | 12/22/2017 4:36:51 PM
By Dan Gill
LSU AgCenter Horticulturist
(12/22/17) Our winter landscapes look decidedly different from our landscapes in summer for two major reasons. First, many of our shade trees drop their leaves in winter, and in their leafless state their appearance is stark and bare. In addition, our lawn grasses go dormant in winter and turn brown.
Lawns can be overseeded with ryegrass if a green winter lawn is desirable (and you don’t mind continuing to mow). But nothing can be done about the trees.
Plants that drop all their leaves at one time and enter a leafless, dormant state are called deciduous. In climates that experience cold winters, such as the northern U.S., this leafless time for trees and shrubs is during winter when sub-freezing temperatures occur.
When the ground freezes, it is difficult for plants to absorb water from the soil. Leaves are the part of a plant most responsible for water loss. So trees and shrubs in cold climates where the soil freezes tend to be deciduous because of a lack of available water. (Deciduous plants also occur in the tropics where plants have generally evolved a deciduous habit to cope with a dry season when little or no rain falls.)
In addition, it is hard to protect broad, thin leaf tissue from extreme cold. And the broad leaves of trees such as maples, elms and oaks will catch the snow, leading to branch breakage.
So trees and shrubs with broad leaves simply shed them in fall and put their effort into keeping important buds, twigs and branches alive through winter. Losing their foliage helps broad leaved trees and shrubs get through winters in cold climates. And, yes, species that have evolved a deciduous lifestyle retain it even when they grow in milder climates like ours.
Conifers, such as pines, firs and junipers, are about the only trees that keep their foliage during northern winters. These trees produce scale-like leaves or needles instead of broad leaves. Conifers are shaped to shed or withstand the weight of snow, and the needles are designed to conserve water. So these trees are able to retain their foliage over winter.
Virtually all other northern trees are deciduous. When a Northern gardener or gardening book uses the term “evergreen” in reference to trees, it is generally synonymous with conifer. In the mild winter climate of Louisiana (and the South in general), a number of evergreen trees are not conifers; live oak (Quercus virginiana), hollies (Ilex species and hybrids) and Southern magnolia (Magnolia grandiflora) are notable examples.
We commonly use evergreen trees in our landscapes, but deciduous trees are the backbone of our shade tree planting. This is because we generally prefer to use trees that provide welcome shady relief from the hot, intense sunlight of summer but drop their leaves and allow the welcome warmth of the sun to shine through in winter. So deciduous trees are useful and welcome in Louisiana landscapes, even if they do look bleak in winter.
When it comes to shrubs, however, deciduous plants are not preferred. Here in Louisiana, we have a vast selection of evergreen shrubs to choose from that retain their leaves year-round. And Louisiana gardeners use evergreen shrubs almost exclusively. Although we accept and use deciduous trees in our landscapes, heaven forbid a shrub should drop its leaves during winter. Few gardeners will choose shrubs that look like “a bunch of dead sticks” during winter.
That’s a pity, because many excellent deciduous shrubs can be used effectively to enhance Louisiana landscapes. A few that have gained acceptance include hydrangea (Hydrangea macrophylla), quince (Chaenomeles speciosa) and bridal wreath spirea (Spirea cantoniensis), but there are lots more we could use. Many of our outstanding native shrubs are deciduous, including red buckeye (Aesculus pavia), American beautyberry (Callicarpa americana), Virginia willow (Itea virginica), honeysuckle azalea (Rhododendron canescens) and oakleaf hydrangea (Hydrangea quercifolia). Balking at the use of deciduous shrubs deprives landscapes of many desirable plants.
Of course, I’m not advocating that we use mostly deciduous shrubs in our landscapes. We are fortunate that our mild climate allows us to use a lot of evergreen trees, shrubs, ground covers and herbaceous perennials. This helps provide a certain continuity of appearance through the year. I would not want a landscape that looks totally bare in winter when my neighbor’s yard is still lush with foliage. But I have found that mixing some deciduous trees and shrubs into a landscape does two things.
First, I think it is desirable to have a landscape that changes its appearance with the seasons. The falling leaves and bare branches of deciduous trees and shrubs in autumn and winter create a striking contrast to how the landscape looks in spring and summer. And new leaves emerging from bare branches signal the beginning of spring in a way that new growth on evergreen trees and shrubs never can.
Second, it creates a whole new personality for a plant. Take the crape myrtle, for instance. With its filigree canopy of branches and smooth, muscular trunks, it is a work of art in wintertime. And oakleaf hydrangeas show off the striking peeling bark of their stems best when the leaves have fallen.
When all the leaves have fallen, and they are nestled snugly in beds as mulch or fill our compost piles, don’t despair at the barren branches. Instead, let’s appreciate the unique beauty of deciduous trees and shrubs during their leafless period.
Changing colors of trees create an attractive contrast to evergreen trees in the Louisiana winter landscape. Photo by Rick Bogren/LSU AgCenter
The bare branches of this crape myrtle present an interesting pattern in the winter landscape. Photo by Rick Bogren/LSU AgCenter