We have found that as the trees mature they become more hardy, in about 2 years time we are fairly sure that the trees will be able to withstand most temperatures. Hardiness trials in Japan, USA and Germany have seen trees survive temperatures down to -12 degrees C. Make sure that you aclimatise the tree before putting it out. Ensure that this is done gradually so that the plant does not suffer undue stress.The optimum time for conditioning a plant to its new environment is when the weather conditions are mild, rather than extreme heat, wind or cold.