@ame @openstreetmap Some thoights about mapping hotanical gardens from 13 years ago http://sk53-osm.blogspot.com/2013/09/a-quartet-of-botanical-gardens.html.
I'd be cautious about mapping small plants such as herbs even in a botanical garden. Beds get swapped around for all sorts of reasons, but the actual dedicated bed tends to remain and I think that is the sensible base unit. There is a tag landuse=flowerbed for this, but I regard the use of the landuse key as unfortunate.