I've been using commercial vinyl plant tags and old Venetian blind slats for years, with excellent results. Common plastic just degrades too quickly for all but the most temporary of purposes.
Interestingly, the last set of blinds I rescued from the trash hasn't held the writing very well at all - it fades within 6 months. I don't know if it was the grade of vinyl, or maybe some kind of cleaning/waxing residue on the blinds. (I'm using Sharpie permanent markers.)
Now I mark both ends of the tag, using pencil on the above-ground end, and Sharpie markers below. Pencil never fades, but it can smear from contact with the soil.
When I need extra long-lasting tags, I cut them from aluminum cans, emboss them with a ballpoint pen, and tie them to the plant itself or a stake.
Ken
East S.F. Bay Area
USDA zone 9
