Last week when I went to Soule's Gardens to buy some hostas, I saw a wonderful idea for plant markers. Cynthia, the owner of Soule's, uses polished rocks with the names of the plants written with paint pen to mark the names of her plants. [She also buries a tag in the ground at the 2 o'clock position on all her plants just in case some child decides to play rock collector.]
Cynthia told me that the rock tags have lasted for more than two years for her without getting washed off or faded. She told me to make sure that I used paint pens and polished rocks.
I went to a big box store and found some bags of polished rocks in the candle section and some paint pens in the craft section. I bought black, white, and gold pens to see which one looked best and was easiest to read.
I think that the gold one was the prettiest and easy enough to read, so I made most of my rock labels with the gold pen.