A month or two ago urg had a discussion on labelling plants in a
durable way. Someone suggested using a pyrographic pen.

I acquired one and have used it to make labels on pieces of
hardwood, about 1/2 inch wide and 8 inch long. The tool was easy to
use, provided the name was sketched out on the wood with a pencil
before burning it in. I am very pleased with the result. It remains
to be seen how they get through the winter.

Franz