First of all, no our customs and border guards are not issued any kind of sense of humor at all.
What Susan found on Yahoo is pretty much how it works. The horseradish I sent to Alix in Canada last year I sent 'undercover'
because they wanted raw foods to have been 'processed' to a certain minimum. This meant I would have had to do stuff to the horseradish that would have rendered it unable to grow, and that is why I was sending it to Alix: so she could grow it.
So, if you have harvested it, cleaned it up, sterilized it, and it is no longer able to be grown you should be alright....