I could think of the Epcot's The Land. There is or was a tour, but I think is by reservation. They show the garden they use to grow the food for their restaurants. Usually you see it on The Land ride. I did remember they where doing those, but I don't know if they are still doing it.
Outside of Disney, you have to go to Downtown Orlando for the Leu P Gardens. That is the closest I could think off!