The advice to clean the soil from plant roots before shipping is practical from many aspects. First, why pay postage to ship dirt. Secondly, it helps to remove organisms which may be benign in your area but extremely invasive in another. I have seen with bulbs shipped from Holland, there is a mandatory certification of being soil free for that very reason. When I shipped iris rhizomes to many different states, I washed them in soapy water with a generous dose of bleach added. As far as packaging goes, damp peat moss or shredded paper works. Damp sawdust is not recommended now due to serious infestations of a beetle which destroys ash trees.
