Hi Aaron,
I don't know much about the restrictions (maybe some of the grower/commercial guys on this site do?), but here are a couple of thoughts for you:
- a quick scan of the usda.gov site shows some hits when I searched on "import trees". Some of them relate to CBP regs... e.g.
(that one includes tables about different countries, though it's possibly about other plant materials).
- Another option you might consider, as a way to keep your co-worker away from some of the risks at customs crossings, would be to ask him to post them (mail system). While that may or may not be allowed to "get through", it'd at least remove the risk of delays at his personal border crossings. (Though I've got no idea about the comparative effort on his part to post rather than carry).
Just a couple of ideas.
Mike central NY state, zone 5