Are letters sent via airmail exposed to freezing temperatures?
It’s very likely that the temperatures inside the hold of airplane are close to freezing. Now I say likely because the outside temperature at altitudes can be oh -60°F or so. Also, I have never had frozen toiletries, pets survive, and some very quick web searches say the same. Your seeds could probably be packaged in such a way that they are protected during the flight (large box, foam packing, etc).. The real danger is sitting on a tarmac in some obscure location while not in flight. sometimes packages are unloaded and left in the open while waiting for loading onto the next flight. I’ve shipped boxes to japan that spent 24 hours sitting on a tarmac in Anchorage Alaska for example. The shipper can request special handling like temperature controlled shipment. Good luck.
