Draining the containers in the late fall served two functions. It removed extra water weight before the roof has to contend with the winter ice and snow load, and hopefully it will prevent container and root damage by removing the most likely source of expansion and contraction in the container - water. We like to over engineer, so after draining the containers we move them all up onto the flashing that caps the support walls of the building, and then wrapped the drained bins in waterproof tarps. All that debris in the foreground compost heap? Dead plant material, and compostable coffee and tea cups we keep up top for guests and work parties.