Magnolias are hallmarks of the southern landscape with their large, glossy-green leaves, fragrant flowers, and stately forms. However, not all magnolia cultivars can rise to the expectations of homeowners and landscapers. A long-term AAES study is helping identify the best magnolia cultivars for Alabama.

        The study began in December 1983 when 12 southern magnolia (Magnolia grandiflora) selections were added to a comprehensive tree evaluation project underway at the AAES’s Piedmont Station in Camp Hill. The magnolia planting is part of a larger tree study that was established at the Station (located in USDA Plant Hardiness Zone 7b) in 1980 and includes more than 200 species of trees. For the magnolia study, young trees were planted 25 feet apart within rows and 30 feet between rows and no supplemental irrigation was applied except at planting. While trees originated from several nursery sources, all trees were container-grown prior to field planting and were of similar size at installation. A complete fertilizer (13-13-13) was applied at planting and reapplied in subsequent years in early spring at one pound of nitrogen per one-inch of caliper. Weeds were controlled using chemical pre- and post-emergence herbicides. The trees were not mechanically pruned, though all cultivars in the study sustained minimal deer damage during the first year after planting.

       The trees were evaluated on growth characteristics and leaf quality (see table). Growth rates were determined by recording tree height, canopy spread, and caliper (the diameter of the trunk measured at 12 inches above the soil line) annually. Leaf size and color evaluations were conducted in September 2000 on recently matured leaves harvested three nodes behind the terminal. A portable Minolta spectrophotometer (CM-2002) was used to rank in a nonsubjective manner the difference in the color of the underside of the leaves among each selection. Flowering duration also was evaluated.

       Certain growth and leaf characteristics are considered important within the industry. For example, ideal leaves are glossy and deeply green on the upper side and a fuzzy, rich brown on the underside. Trees also should experience only minimal leaf shed (leaf drop) throughout the year. Cultivars that bloom over an extended period of time also are preferable, and trees that grow symmetrically and exhibit consistent growth patterns are considered superior. Ideal tree shapes vary depending where the trees will be used in a landscape. Taller, more conical trees are often needed for tight spots in a landscape, while wide-spreading trees may be best for open areas. The important aspect is that the trees selected for a site display consistent growth characteristics.

       In general, the seedling selections from a native population near Mobile, Alabama, and the cultivar ‘Margaret Davis’ demonstrated the greatest overall growth based on total height, caliper, and canopy width. The cultivar ‘Smith Fogle’ also exhibited similar height growth to these selections (see the table). Least overall height growth was exhibited by ‘Little Gem’ and ‘Majestic Beauty’. ‘Hasse’, with a canopy width of 11.6 feet, and ‘Little Gem’, with a canopy width of 13.9 feet, demonstrated the narrowest growth. Hasse had a smaller caliper than all other selections in the study with the exception of ‘Aldridge’, ‘Little Gem’, and ‘Majestic Beauty’.

       Overall, the Magnolia grandiflora seedlings, included as representatives of the species, were among the most aggressive growers in the study, but were highly variable from tree to tree in form, leaf morphology and anatomy, and canopy density. This would be expected of seedling magnolias because unlike cultivars, which are clones of their parents, seedlings have potential for genetic variability. Only one seedling in this study was attractive enough for commercial potential with few if any unusual or outstanding characteristics evident in the other seedlings.

        Aldridge, a seedling strain from Aldridge Nursery in Von Ormy, Texas, was included in the study because it was bred to bloom at a young age, typically one year to 18 months. There was little variability in growth characteristics of the Aldridge trees in this study and blooming began in the second year of the study (1985). The Aldridge trees also exhibited an extended blooming season, often lasting through the end of July; however, the foliage was the lightest green of all selections and leaf drop during stress was common.

        Three unnamed, numbered selections (SG#4, SG#5, and SG#6) were included from Shady Grove Plantation in Orangeburg, South Carolina. SG#5 has since been released as the cultivar ‘Smith Fogle’. ‘Smith Fogle’ has an attractive ovate-pyramidal form with dense brown backs to leaves that are dark green and larger than SG#4 and SG#6. Leaf drop for ‘Smith Fogle’ was similar to other cultivars. SG#4 was dropped from production by Shady Grove, and SG#6 is still in production there, but has not yet been registered as a cultivar.

        One of the most attractive trees in the study was ‘Hasse’, which displayed a narrow upright form, small leaves with dark brown backs, and unusually good leaf retention throughout the year. ‘Little Gem’, a dwarf selection, also had good leaf retention and featured small, deep green leaves and dark brown leaf backs. While height through1999 reached approximately 24 feet, ‘Little Gem’ has a bunchy, shrub-like form as if having been top-pruned. ‘Little Gem’ has the longest blooming season of all trees in the study, with sporadic blooms from May through the fall.

        ‘Claudia Wannamaker’ produced an attractive form well suited for large spaces with a medium growth rate compared to other cultivars in this study (see table). The foliage is acceptable, but with only dusty-green to light brown undersides to the leaves. ‘Margaret Davis’, which has a broad open canopy, could also be used where a large growing magnolia is needed. The leaves have light brown undersides—not outstanding but somewhat attractive.

        Perhaps the least attractive cultivar in this study was ‘Majestic Beauty’. Its leaves are the largest of any in the study, but they also are the lightest green of all but the Aldridge strain with pale green undersides. Also, the growth habit overall is irregular, lacking any particular characteristic form. The seedling selections and ‘Majestic Beauty’ had the largest leaves overall with the smallest leaves on ‘Little Gem’. Cultivars ‘Bracken’s Brown Beauty’, Hasse, and ‘Little Gem’ had the darkest brown backs, considered highly desirable in the industry. ‘Majestic Beauty’, the seedlings, Aldridge, and ‘Smith Fogle’ leaf undersides were smooth and hairless (glabrous), which generally is regarded by the industry as an undesirable trait.

        The benefits of AAES tree evaluations are significant. Such long-term observations are rarely feasible in commercial nurseries primarily concerned with growing and marketing the best selling plant materials. Such plantings also are unlikely to occur in a replicated fashion in long-term sites, such as arboreta that are primarily concerned with display of numerous species in limited quantities. Furthermore, environmental conditions change such that long-term field observations are particularly valuable as a reference point for landscape use as opposed to the often rapid and somewhat artificial growth responses available from short-term container studies. The Auburn University Shade Tree Study site continues to be maintained for grower observations, seed collection, and tours. However, due to the remote location about 25 miles from campus, visits must be scheduled ahead of time in most cases.

Sibley is Associate Professor, Creech is Research Associate, Gilliam is Professor and Department Chair, and Williams is Associate Professor, all of Horticulture; Owen is former Superintendent of the Piedmont Station.

Top             Table of Contents