Overwintering Ability Of The Introduced Species And Cultivars Of Lagerstroemia In Beijing

As excellent summer-watching-flowers tree in China’s northern cities, crape myrtle is still facing the problem of low winter surviving rates in Beijing area. In this study, the cold resistance of3Lagerstroemia species and50cultivars were appraised to select cold-resistant cultivars. In addition, the change of physiological indexes of crape myrtle cultivated outdoor during winter period in Beijing were used to determine the critical point and main factors for Lagerstromia survival and provide theoretical basis for expanding its landscape application. The major results are as follows.(1) Cold resistance of3Lagerstroemia species in the order from strong to weak was L. subcostata, L. caudata, L. limii. Arbor crape myrtle cultivars whose cold resistance considered to be stronger were ’Choctaw’,’Bai Yun Ying Xia’,’Osage’,’William Toovey’,’Muskogee’,’Comanche’; Crape myrtle shrub cultivars whose cold resistance considered to be stronger were’Velma’s Royal Delight’,’Tonto’,’Fu Jian Za Zhong Bai’,’Victor’,’Hopi’,’Dallas Red; Crape myrtle dwarf cultivars whose cold resistance considered to be stronger were’Okmulgee’,’Houston’,’Chickasaw’. Taking ornamental characters, the difficult degrees of propagation and cold hardiness into comprehensive consideration, the following crape myrtle cultivars were recommended for landscape application in Beijing. Arbor type:’Yuma’,’Dynamite’,’Sarah Favorit’,’Comanche’; shrub type:’Victor’,’Tonto’,’Arapahoe’,’Pocomoke’,’Carolina Red’,’Centennial’,’Dallas Red’,’Powhatan’,’Zuni’; dwarf type:’Houston’,’Okmulgee’.(2) Freeze injury and shoots shriveling caused the difficulty to overwinter for crape myrtle in Beijng. The low temperature was one of the primary factors to cause shoots shriveling, excluding spring drought. The lower branches of Lagertroemia plants proned to freeze injury, while the upper branches proned to shoots shriveling. Shoots shriveling happened from the middle February to the early March. It often happened when the water content was below20～25%. In landscape application, it is suggested that hilling and pruning can be used to protect crape myrtle during the winter.