[ Whats the Greenhouse makes him blink for a few moments, a little surprised at the question cause surely the plant boy... Then smile because, well, if he never went that way- ]

Look for the house that looks like it's made of sweet gingerbread. Across from it is a smaller building which is the Clinic, and attached to the Clinic is the Greenhouse. You will recognize it, as it is warm and full of plants which will bloom year round, and has walls of glass. There should be a door that opens to the outside, so you need not enter the Clinic proper if you merely wish to visit the Greenhouse.