It has been a few days since you posted your question, and no one has responded, so I'll tell you the LITTLE I know. When you come back into the US (by air, at least) you are required to fill out a declaration of what you purchased or acquired on your trip. It specifically asks about plants, plant material, and soil. Any plants brought into the US need a certificate that they are "sanitary." Maybe others can tell you how you get the certificate. At the airport, if you have anything "to declare," like plants, you have to go through a different line at customs. I've never brought anything like this back, so I don't know how that goes (other than slower).

Ginny: A few years back, not so long ago, one JUST ONE, bug was discovered in Florida. Know what the State did?
They sprayed THE WHOLE STATE. They burned something like
two million trees. That is why they're very concerned about people who think about bringing something nice back home.
My advice. When in doubt...DON'T.

Going through customs Labor Day evening in Boston after deplaneing from Air France with a declared live plant, nothing happened. Noticed that they were merely spindleing the declaration forms without reading any. So far no federal agents in swat jackets at my door.

Hi Ginny, I think that taking plants out of places like Europe would be easier than places like the Canary Islands. I've been to both the Canary and Cook islands and my most vivid memory was having a man in a gas mask come on board the plane when it landed and before it took off to spray for bugs!! We passengers did not have gas masks, and it was pretty scary. When we got to Tahiti, they took all of our luggage away from us (even our carry-ons) and took it out into the jungle and bombed it with an insect killer. We didn't get it back until the next morning. I think you could say that these islands are pretty paranoid about bugs. If I were you, I'd stick to commercially prepared seeds. I've taken those out of many different countries without any problem at all (including from several islands in the Caribbean, Bermuda, Cook Islands, Tahiti, Bora Bora, Hawaii, Australia, New Zealand and England).