Definitely not a warehouse.
The Florist (花屋, hanaya) is an area accessible from the Gray Road by interacting with a small shrub northeast of the entrance to the train tracks.
Entering from the Gray Road, the first area encountered resembles a brightly lit greenhouse, with long troughs filled with soil and (sometimes unusual) budding plants & flowers. At the end of the greenhouse is a red jack-in-the-box which, when interacted with, will take you to a dark, dank-looking laboratory filled with walking plants.
Moving to the right from the room with the jack-in-the-box, there is a grey metal door that leads to a small sub-section of the laboratory inhabited by a red sprout-like creature with a yellow eye, which will stop moving if you use the Crossing effect near it.
Back outside, there is a large doorway on the right side of the room that leads to an area filled with glass tanks, some of which contain flashing hearts and growing plants. There is another door at the end of this room which leads to a small bedroom with a some more tanks and a few bookshelves, along with a barred window.
Through the door in the bedroom is a study, containing a few more bookshelves along with a small desk, and a large beaker filled with a green liquid. Here, you can find a red lips-esque creature, which turns on a switch if you interact with it, although this doesn't currently do anything.
Interacting with beaker will take you to an isolated room in the Cocktail Lounge with a single Mandrake NPC and the beaker full of green liquid with a straw in it, apparently served as a drink.
After visiting this area at least once a Green book will appear in lower section of the Library, which appears to be some kind of gardener's handbook.