Richard Bogren, Gill, Daniel J.
By Dan Gill
LSU AgCenter Horticulturist
(11/17/17) Fall — November through early December — is the best time to plant hardy trees in Louisiana. Are you thinking about adding shade trees, small spring- or summer-flowering trees or trees for screening? If you are, this is time of the year to head out to local nurseries and purchase trees to plant in your landscape.
If you want a medium-sized evergreen tree, the evergreen sweetbay magnolia (Magnolia virginiana var. australis) is an excellent native tree that is not nearly as well-known as it should be. Because of its outstanding characteristics, the evergreen sweetbay magnolia was chosen to be a Louisiana Super Plants selection by the LSU AgCenter.
The Louisiana Super Plants program is an LSU AgCenter educational and marketing campaign that highlights tough and beautiful plants that perform well in Louisiana landscapes. Louisiana Super Plants are “university tested and industry approved.”
The Southern magnolia (Magnolia grandiflora) is well known as a traditional tree for Louisiana landscapes. Like camellias, azaleas and crape myrtles, it is often considered essential for creating a “Southern” style garden. Unlike camellias, azaleas and crape myrtles, however, which are all native to the Far East, the Southern magnolia is native to Louisiana. But we have other native Magnolia species that are also worthy of planting.
The evergreen sweetbay magnolia reliably retains its foliage during winter. This naturally occurring variety is distinct from the standard species, Magnolia virginiana, for this reason. The standard species is deciduous to semi-deciduous and drops most or all of its leaves during winter. The evergreen form grows in the most southern parts of this species’ natural range in the eastern U.S. In the Latin name, the variety name australis means southern.
And speaking of the leaves, the foliage of the sweet bay magnolia is especially beautiful. Smaller and lighter green that the Southern magnolia and without the glossy shine, there is a surprise when you look closely. The foliage of the sweetbay is bright silver-white on the reverse. When the wind catches the canopy of these trees and flips up the leaves, the ripples of silver are a delight to the eye.
The flowers also make this tree popular. They are creamy white and about 2-3 inches in diameter. Flowers generally appear in greatest abundance beginning in late April, peaking in May and diminishing in early June. But flowering may continue sporadically through the summer. They are not as large and showy as the flowers of Southern magnolias, but they have the same rich, lemony fragrance that many Louisiana gardeners know and love so well.
The sweetbay magnolia is a medium-size tree that grows to be around 30 to 50 feet tall with a spread of 20 to 30 feet. The tree tends to be fairly narrow and columnar through much of its life, although the shape can vary. Given its potential size, make sure you do not plant them too close to buildings.
This attractive tree can be grown either multi-trunked or single-trunked. When growing a multi-trunk specimen, limit the number of trunks to three or five. Younger sweetbay magnolias may send up vigorous shoots from the lower trunk. Once you have established the desired number of trunks — one, three or five — keep these shoots pruned off.
Sweetbay magnolias are best planted while the weather is cool and the plants are dormant. Fall planting is particularly good because it allows the tree to grow roots and get established over the winter.
Magnolia roots are very sensitive to the depth of plantings, so it is critical that the top of the root ball be at or slightly above the surrounding soil. If planted too deeply or in a location not to their liking, magnolia trees tend to grow poorly and stay stunted. A happy young tree, on the other hand, will grow moderately fast, especially if fertilized in spring each year.
Be aware that even though they are evergreen, sweetbay magnolias drop some old leaves in fall and may drop a few more as they come into bloom. They also drop old petals when they are in bloom and seed cones in late summer and fall. But I would not consider these trees as messy as the popular Southern magnolia.
Planting trees properly can make the difference between success and failure.
When preparing the hole, dig the hole at least twice the diameter of the root ball and no deeper than the height of the root ball. When placed into the hole, the root ball should sit on solid, undisturbed soil.
Remove the tree from its container and place the tree gently in the hole. The top of the root ball should be level with or slightly above the surrounding soil. It is critical that you do not plant the tree too deep.
Thoroughly pulverize the soil dug out from the hole and use this soil — without any additions — to backfill around the tree. Add soil around the tree until the hole is about half full, then firm the soil to eliminate air pockets but do not pack it tight. Finish filling the hole, firm again and then water the tree thoroughly to settle it in. Generally, do not fertilize a newly planted tree.
Sweetbay magnolia flowers are creamy white and about 2-3 inches in diameter. Photo by Dan Gill/LSU AgCenter
Mature sweetbay magnolia trees will average about 30 feet tall with a spread of 20 feet, but larger sizes are not uncommon. LSU AgCenter file photo by Allen Owings
The sweetbay magnolia produces bright red seeds that mature in autumn on cone-like pods. Photo by Dan Gill/LSU AgCenter