Hi Snow, At Divine Spirits we have a number of articles/posts about herbology as probably many of the other covens do aswell, I i'm unsure if there is a coven solely devoted to only the use of herbs though.
This is a very good website for learning the magical properties of herbs.
Just remember though that certain herbs can be extremly poisonous so always double check you dont use such herbs for drinking/ingesting ect.
Also you are bit unclear of what it is you exactly want to learn about herbs..is it how to make infusions,herb pouches,teas? ect