Answer: According to Michael Dirr's "Manual of Woody Landscape Plants", Cedrus deodara is hardy to 0 to 10 degrees. He mentions that there are reports of the tree withstanding minus 12 degreees but he does not believe them to be true. The Monrovia plant catalog indicates a hardiness range of 0 to 10 also, and this would be USDA cold hardiness zone 7. Atlas Cedars (Cedrus atlantica), it is interesting to note, are considered one zone hardier, to zone 6. To some extent your success would depend on the microclimate in the exact location where you keep them because a sheltered location, wind exposure, refleced heat from buildings and so on can all contribute to the microclimate and sometimes mitigate the cold enough to make a fairly substantial difference. I'm really sorry I can't be any more encouraging than that.
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