Canadian Forest Service Publications
Chilling units used to determine rooting of stem cuttings of junipers. 1990. Major, J.E.; Grossnickle, S.C. Journal of Environmental Horticulture 8(1): 32-35.
Issued by: Atlantic Forestry Centre
Catalog ID: 28965
Stem cuttings of Juniperus chinensis cv. Pfitzer Aurea, J. horizontalis cultivars Bar Harbor, Prince of Wales, Wiltoni and Youngstown, J. procumbens cv. Green Mound, J. sabina cultivars Broadmoor, Buffalo and Tamariscifolia and J. scopulorium [J. scopulorum] cv. Wichita Blue, collected twice monthly from 15 Oct. 1986 to 28 Feb. 1987, were dipped in an IBA or NAA rooting dip (concentrations given) and inserted in rooting beds with bottom heat at 18degreesC and misting as required. The air temperature 1 m above the stock plants was monitored continuously and the seasonal chilling units (the number of hours when the temperature was <= 5degrees) were determined. The chilling units experienced by stock plants affected the rooting response of cuttings taken from them. Cultivar variations in percentage rooting and rooting pattern were marked. It is concluded that rooting success is related to the physiological status of the donor plant. Calendar dates can be used successfully as a guideline for cultivars known to root effectively over a large number of chilling units (such as Youngstown, Bar Harbor and Price of Wales). However, the chilling unit concept may be more appropriate for determining the optimum period for successful rooting of cultivars that have a more precise response to chilling units experienced (such as Tamariscifolia, Broadmoor and Green Mound).