Because so many things derive from these plants and tools, a Herbologist's job is essential in the wizarding world.
You could be your standard Herbologist, carrying little jars around with you in your pockets and pulling them out to unsuspecting Halloween party-goers, explaining their magical properties and what-not. It is quite a fantastic field of study for obvious reasons. If that doesn't suit your tastes, dress it down to your everyday Botanist and do the same thing, just with natural plants. If so, they should check out our officially licensed Harry Potter Herbology Costume for Kids.