A person who is an expert on grass is often referred to as a "turf scientist" or "turfgrass specialist." They study the Biology, cultivation, and management of grass species, particularly in relation to lawns, sports fields, and Golf courses. Additionally, a botanist who specializes in grasses may also be called a "grasses expert" or "grasses botanist."
A Travel Expert
A person who is an expert in grammar is called a linguist or a grammatician.
a gardener
Such a person is a dietician, being an expert on diet and nutrition.
A slight of hand artist.
Expert gunner.
A person who mows the grass on a baseball field is called a groundsman.
Oh, dude, people call the grass "grass" because... wait for it... it's grass! I know, mind-blowing, right? It's like calling water "water" because it's water. So profound.
A person who is an expert in many languages is called a polyglot. This term is used to describe someone who has a high level of proficiency in multiple languages.
A person who is knowledgeable is often referred to as an expert, scholar, or well-informed individual in a particular field or topic.
Expert, Knowledgeable, etc..
A person who mows the grass on a baseball field is called a groundsman.