Remembering what you planted where is the constant problem for many gardeners, especially those with wandering minds, or larger than average gardens (or both).
The other job is finding where the plant label disappeared too. This solves both problems because it allows the label to be displayed well clear of the ground.
It also could be used imaginatively on a wedding or Christmas table for place or table names.
Write the names on the slate with chalk or a white chinagraph pen (not supplied)