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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Publications at this Location » Publication #352376

Title: Growth, cold-hardiness, and flowering of Osmanthus in Tennessee

Author
item Alexander, Lisa

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2018
Publication Date: 2/11/2019
Citation: Alexander, L.W. 2019. Growth, cold-hardiness, and flowering of Osmanthus in Tennessee. HortTechnology. 29:78-84.

Interpretive Summary: Production and use of Osmanthus as a landscape plant is currently limited to USDA Hardiness Zones 7 – 10, and nursery growers wish to extend the range of Osmanthus species into colder climates. In order to provide recommendations to growers and landscapers and inform breeding efforts for cold-hardiness improvement, ARS scientists in McMinnville, TN conducted a replicated Osmanthus trial was in a USDA Hardiness Zone 6b/7a transition zone. Sixteen Osmanthus cultivars representing four species were evaluated for growth, stem necrosis, and flowering in a pot-in-pot production system from 2015 – 2017. The most-cold tolerant cultivars were O.heterophyllus ‘Kaori Hime’, ‘Hariyama’, ‘Shien’, ‘Rotundifolius’, and ‘Head-Lee Fastigate’; O. xfortunei ‘San Jose’, and O.armatus ‘Longwood’. Of these cultivars, O.heterophyllus ‘Kaori Hime’, O. xfortunei ‘San Jose’, and O.armatus ‘Longwood’ flowered under winter-exposed conditions. Osmanthus fragrans cultivars were generally not hardy, although ‘Fudingzhu’ flowered each year under winter-exposed conditions. Plants selected and produced in transition zones are often suitable over a wide geographic and climatic area, and these results will be used by growers and landscapers to inform choice of Osmanthus cultivars to plant and/or sell.

Technical Abstract: Production and use of Osmanthus as a landscape plant is currently limited to USDA Hardiness Zones 7 – 10, and nursery growers wish to extend the range of Osmanthus species into colder climates. In order to provide recommendations to growers and landscapers and inform breeding efforts for cold-hardiness improvement, a replicated Osmanthus trial was conducted in a USDA Hardiness Zone 6b/7a transition zone. Sixteen Osmanthus cultivars representing four species were evaluated for growth, stem necrosis, and flowering in a pot-in-pot production system from 2015 – 2017. Half of the plants in each cultivar were removed to winter protection each November and returned to the field each May. There were significant differences in growth and cold-hardiness among cultivars. Percent increase in the growth index after three growing seasons for winter-exposed accessions of O.armatus, O.xfortunei, O. fragrans, and O. heterophyllus averaged 867%, 1,175%, 155%, and 6,361%, respectively. Percent stem necrosis in May 2017 for O. armatus, Oxfortunei, O. fragrans, and O. heterophyllus averaged 1.1%, 2.7%, 44.8%, and 20.2%, respectively. The most-cold tolerant cultivars were O. heterophyllus ‘Kaori Hime’, ‘Hariyama’, ‘Shien’, and ‘Head-Lee Fastigate’; O. xfortunei ‘San Jose’, O. heterophyllus ‘Rotundifolius’, and O. armatus ‘Longwood’. Of these cultivars, O. heterophyllus ‘Kaori Hime’, O. xfortunei ‘San Jose’, and O. armatus ‘Longwood’ flowered under winter-exposed conditions. Osmanthus fragrans cultivars were generally not hardy, although ‘Fudingzhu’ flowered each year under winter-exposed conditions. Evaluation and breeding efforts are continuing to extend the range for production and growth of this genus.