Cold Hardiness of Ilex glabra Cultivars from Field Trials and Laboratory Tests

Abstract To evaluate the cold hardiness of Ilex glabra (L.) A. Gray (inkberry) cultivars and provide growth and cold-hardiness data for growers as references for production and marketing, field trials and laboratory tests were conducted in 2007–2008 and 2008–2009. Plant survival was 72 and 93% for the 2007 and 2008 planting, respectively. Ilex glabra ‘Shamrock’ was the most cold-hardy cultivar; Ilex glabra f. leucocarpa, ‘Viridis’ and ‘Nigra’ were the least cold-hardy cultivars; and Ilex glabra wild species and its cultivars including ‘Compacta’, ‘Densa’, ‘Chamzin’, and ‘Pretty Girl’ had intermediate cold hardiness. Based on controlled freezing tests of Ilex glabra cultivars, the temperature that results in 50% relative electrical conductivity (REC50) of Ilex glabra cultivars ranged from −19.4 to −31.8C (−2.9 to −25.2 F) for January 2007 and−17.8 to −37.5C (−0.1 to−35.5F) for January 2008. The cold hardiness rates from field trials were significantly correlated with the REC50 values from laboratory tests. The factors influencing cold hardiness, including plant cultivar, tissue, temperature, deaacclimation, winter desiccation, and others (e.g. mechanical injury, snow pack) should be in consideration.