When I have excess daylilies and I want to keep up with their names I use the old vinyl bind slat system. I also am using them for my seedlings along with recording their location here on NGA in my plant list.
I dug two sets out of the trash by the road just yesterday and had retrieved a set about a week ago, so now I am pretty well set for labels for a while. After you learn how to remove the cords, and discover the slats just slip out of all those threads it does not take long to prepare them for becoming labels. I can cut 4 to six slats at a time with my shears.
There are a lot of disadvantages to using these vinyl slats, but they are cheap and easy to work with and most of the disadvantages can be overcome by using a map or some other method of recording the locations, even burying a label at the end of the row would really help.
The PVC pipe idea is great, but you still have to make your labels(you could just write on them I suppose) and the main drawback I see with them is storage. I can store hundreds of vinyl shade slats in a very small space and have them available when needed.
The big advantage of the PVC pipe is the durability of them.
Here are some photos of how I am using them.
Seedlings in beds.
Some various methods of marking them.
I use the string I remove from the blinds to bind stacks of them together, I cut the long ones in half so they are easier to store.
Here is a typical marker after being cut and written on with the grease pencil.
This is certainly not for any long term projects, but for a year or maybe two it works quite well (most of the time).