The Kubrick Mini Gardens is a small area in the centre of the ground floor.
We see a brief signage relating to the mini gardens at about 45 minutes into the film; this must be on the ground floor, as Kubrick Mini Gardens is shown as being in the centre of the ground floor, lot 106:
My guess is that the gardens were curtained off overnight, as they didn’t want zombies wandering around!
Detail Of The Dead 