Try burying a plastic knife with the plant, with the name on the blade in Sharpie. For added protection, you can put a layer of the old fashioned, clear scotch tape over the name. You won't know what it is till you dig it up - but I have had the knives remain for over 10 years and still be easy to read. The roots grow right around them. I usually put the knife in the hole horizontally under the roots.
