Planting Date Affects Survival and Height Growth of Hybrid Poplar

Abstract

In this study I investigated the effects of planting date for soaked versus unsoaked cuttings of two hybrid poplar clones under irrigated versus unirrigated and weedy versus weed-free conditions. Cuttings were planted each year for 4 years. Survival at the end of the first growing season was generally greater than 90% for all planting dates. At the end of the second growing season survival for trees planted before July 16 was again generally more than 90%. However, cuttings planted from July 30 through August 27 showed a major decline in survival and survival of fall planted cuttings ranged from 6 to 90%. Mortality of late summer- or fall-planted cuttings occurred prior to the beginning of the second growing season and was attributed to frost heaving. The tallest trees were not those planted at the earliest possible dates (April in Rhinelander). Instead, the tallest trees at the end of the first and second growing seasons were those planted in early- and mid-May. This optimum planting period was the same regardless of clone, soaking, irrigation, or weed treatment. Actual optimum planting date would change with location and local climatic conditions. Some climatic indices may prove more universal in predicting when to plant. Although tentative, it appears that for best growth, unrooted hybrid poplar cuttings should be planted in soil warmer than 10 °C. Trees do not grow as well if planted immediately after soil frost leaves the ground. Key words: Energy plantations, plantation establishment, woody biomass, intensive culture, Populus.