Given the widespread availability of tropical plants everywhere, you could probably locate one at any time of year. However, I would purchase, transport, and relocate a plant when the temperature is nearly the same inside the store, outdoors, in your vehicle, and inside your home. If I were you I'd wait till spring and pleasant moderate temps. Any plant, esp. a tropical one, will do better if not subjected to an Arctic blast!
i agree, it's getting on the time when it's best to forego purchasing plants. there's still some nice days yet, so you can do it now if you'd like. if it's a windy day, i'd make sure that the plant is in a bag and is well covered (put another one over top of it if needed) so that the chillier temps and any wind are kept at bay while walking to and from the car. a short time in cooler temps won't do too much damage. i definitely don't recommend buying plants when it's freezing out, though!
Till then, you could look at all the beautiful varieties available and decide which one's your favorite! Also, a good reason to prowl through plants at your local retail establishments, and to read up on the care and feeding of a Dieffenbachia. ---I have 3, and like them a lot. Good luck to you and yours!
