I got cedar shims and cut them into thirds. I was very proud for using the table saw all by myself instead of making J do it for me!
Then I got some chalkboard paint and painted away. I highly recommend painting them on something plastic. I first tried newspaper and it stuck to the paint. Then I tried cardboard and it was no better. Let them dry for at least 30 minutes before painting the other side.
The chalkboard paint said to let dry for 72 hours before using. I only waited 48 hours.. oops!
You may be thinking how in the world is chalk going to stay on a label in the rain? The trick is to use a white china marker to write on them. I found one at Hobby Lobby in the drawing supplies section.
When you do want to remove the writing, you can use baby oil and reuse the label.
Now I have labels in my garden: