It would be best to keep the plant in a frost free enviroment initially and plant it out in the spring. We are quite confident that the trees are hardy down to minus 5 degrees C and we know that trees in hardiness trials in the USA and Germany have survived temperature down to minus 12 degrees C but these were more mature trees (5-6 years old). The younger trees may be a little less hardy and will need time to adapt. We are sure that if you plant it out in spring 2007 and give it some protection in the way of fleece the following winter that it will be far more acclimatised and ready to fend for itself.