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  • Author or Editor: Michael Shelton x
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Numerous cultivars of Lacebark elm (Ulmus parvifolia Jacq.) have recently been introduced which are produced vegetatively. Conventional propagation is usually by softwood cuttings under intermittent mist which is quite successful. Softwood cuttings taken off two mature specimen trees stuck in May and June rooted 73 and 93 percent respectively at 10,000 ppm IBA but required overwinter protection prior to lining out the following season. Hardwood cuttings of numerous selections, stuck in perlite: peat (70:30 v/v) over bottom heat at 21°C in a cool greenhouse rooted 60 to 100 percent at 10,000 and 20,000 ppm. Cuttings from winter prunings were taken on February 4, potted by March 12, lined out May 23 produced 69 to 97 cm of growth the same season. The latter procedure offers a low input method of propagation which has several advantages over using softwood cuttings.

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Numerous cultivars of lacebark elm (Ulmus parvifolia) have been introduced recently without adequate testing of their hardiness. A block of commercial cultivars plus numerous experimental numbers were established to observe differences in growth form, ornamental characteristics, and cold hardiness. Laboratory freezing tests were conducted from November to March over a 3-year period to determine acclimation and deacclimation to low temperatures. Stem sections approximately 5 cm long were sealed in test tubes and placed in a low-temperature programmable freezer maintained at 0°C. Samples were cooled by approximately 6°C per hour from 0 to –48°C and held for 1 h at each temperature. Samples were then removed, allowed to thaw at room temperature, and held for 7 to 10 days. Stem samples were sectioned longitudinally to observe browning in xylem and bark tissues. During the winter of 1995–96, no visible injury could be noted on trees in the field in spite of very dry, desiccating weather with temperatures reaching –23°C. Laboratory freezing tests indicated acclimation to –30°C by 18 Dec. 1995 on several cultivars. During warm periods in February, deacclimation occurred on many selections to –18°C, whereas others maintained a killing point of –30°C. Growth form, bark exfoliation, and fall color varied among cultivars.

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