Populus x canadensis 'Hees' This female cultivar has a more or less straight trunk with long, upward-pointing branches. The tree has a broad ovoid crown whose branches later bend downwards. The young leaves emerge fairly late and are light green in colour. The tree produces flowers in the form of female catkins. 'Hees' is very resistant to rust and canker and resistant to leaf spot disease. It is resistant to wind, even in coastal regions. Winter hardiness zone: 4