Planted Tank Guru
Join Date: Feb 2011
Location: Beaverton, Oregon
If you have heat packs the plants should be fine.
Personally I've shipped all around the country at this time of year and they've arrived just fine. The thing is you just can't leave the plants outside in the mailbox for too long. USPS trucks are heated as are their facilities. So the plants will only suffer if they're left out in the cold for too long.
Heat packs are still advised though.