Performance in Northern Florida of Yellow-flowered Cultivars Derived from Magnolia acuminata

摘要

Yellow-flowered cultivars of deciduous Magnolia have become popular for their uncommon, yellow flowers. Breeders have used the North American native Magnolia acuminata as a source of yellow flower color, cold hardiness, soil adaptability and delayed flowering which allows flowers to escape frost damage. Magnolia denudata, Magnolia liliiflora and other Magnolia selections have been hybridized with M. acuminata to introduce larger flower size, precocious flowering and smaller tree size. Currently, about 35 yellow flowered cultivars are available and many additional cultivars are expected to be released in coming years. One of the greatest challenges with yellow flowered magnolias is that yellow flower color often varies in intensity with climate and region. Some selections appear to have less intense yellow color when grown in the southeastern U.S. coastal plain with its associated acid soils and warm, humid climate. Twenty-four yellow-flowered Magnolia selections are planted at the University of Florida, North Florida Research and Education Center, in Quincy, Florida (USDA Cold Hardiness Zone 8b; AHS Heat Zone 9). The purpose of the planting is to screen cultivars for growth, flowering and good yellow flower color in northern Florida (southeastern U.S. coastal plain). Flowering sequence and mean dates of peak flowering are given for 12 well-established yellow-flowered hybrids as well as several Magnolia species. Data for as many as 6 years were averaged to determine mean date of peak flowering, which ranged from 18 February for 'Yellow Fever' to 21 March for 'Maxine Merrill' and 1 April for 'Woodsman'. In comparison, mean date of peak flowering forM. denudata was 12 February and that of a regional ecotype of At. acuminata was 22 March. Relative flower color and size is presented in photographs of flowers from several cultivars placed side-by-side in the same photograph for each year from 2003-2006. 'Butterflies', 'Golden Endeavor', 'Golden Sun', 'Hot Flash' and 'Maxine Merrill' consistently produced flowers with good yellow flower color.