Deciduous magnolias are well adapted to many landscape situations and are highly desirable due to their floriferous nature. About 800,000 flowering magnolias are sold each year in the United States and about 10% of the nurseries that grow magnolias are located in Tennessee (USDA, 2014). There has been interest in breeding for deciduous yellow-flowering magnolias since the 1950s. Most of the yellow-flowering magnolias have been bred from a U.S. native magnolia, cucumber magnolia (Magnolia acuminata), or a smaller statured botanical variety of the species, yellow cucumber magnolia (M. acuminata var. subcordata). This species provides cold hardiness and can be grown in a wide array of soil types. Hybridization with Chinese magnolias [yulan magnolia (Magnolia denudata) or lily magnolia (Magnolia liliflora)] can offer yellow flower color and a range of tree sizes and shapes. Most American magnolias bloom with the foliage, which means a late spring–summer bloom; whereas, the Chinese magnolias bloom before the leaves emerge in the spring. Many cultivars of the yellow magnolias bloom in late March to early April, but often spring frosts and freezes affect flowering as well as leaf-out (Fare, 2011). Cultivars such as Elizabeth, Yellow Bird, and Butterflies were a few of the first commercially available. A second generation of yellow-flowering magnolias with cultivars such as Golden Sun, Golden Gift, Gold Star, and Yellow Lantern were developed by breeders D. Leach and P. Savage; A. Kehr released ‘Gold Cup’, ‘Solar Flair’, ‘Stellar Acclaim’, ‘Sundance’, and ‘Sun Ray’ and in later years, released ‘Sunburst’, ‘Sunsation’, and ‘Sun Spire’. One notable cultivar, Lois, was developed by L. Koerting (Knox, 2001). Yellow-flowering deciduous magnolias are becoming popular landscape plants because they offer an unusual color palette and there are very few yellow-flowering small trees in the landscape plant inventory (Knox, 2002).
This evaluation was conducted at the Tennessee State University Nursery Research Center located in McMinnville, TN (lat. 35.7°N, long. 85.8°W) on the border of USDA Hardiness Zones 6 and 7. The area is known as a climatic and geographic transition zone. Plants produced in this area can be used in landscapes as far north as Zone 5 and as far south as Zone 8. Plant evaluations made in transition zones are ideal because results can be used over a wide geographic and climatic area. The primary objective of this research project was to compare yellow-flowering magnolias for flower color intensity, flower duration, as well as growth rate and canopy form.
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