For inexpensive plant markers that won't blow away, buy an aluminium mini blind (don't use plastic as it may crack) at a garage sale or at one of the big box stores in a sale bin, and from 25 to 50 heavy-duty irrigation staples. Cut mini blinds in the length you need, 3" to 4", measure, and drill holes closer to one side to fit the staples. Write the plant name on the back with a Sharpie, so it wont fade in the shade, and then on the front using a paint pen or a pencil. Carefully thread it onto the staple and then spread a little, as shown in the photo.