Quick to print seed locator, I am using these to plant seeds in the centre of so I know where the seeds were planted in order to not pull them out when removing weeds from the garden. Big enough you could use a sharpie or some sort of outdoor marker to write what type of plant, one side is open for removal once the seedling has grown to an appropriate size, or in case you want to wrap it around an existing plant without disturbing it.

I printed with 1 wall and after cooling it warped a bit so maybe with some infill would be good, but its not really meant to be strong.