The "hang your tomato plants upside down in the garage to ripen after the weather's turned cold" trick is a continuum of #gardening techniques rather than one way to do it.
- you don't need the whole plant (a branch is fine)
- you definitely don't need roots (sheesh)
- it doesn't need to hang, a box is fine (although circulation and keeping the tomatoes from resting on their base is probably a good idea.)
I suspect temperature in the garage matters a bit. Our garage isn't insulated, and aside from not dropping below 40F or so even if it's freezing outside, it's not a great ripening environment - 65-75F is better. A box of branches is more house-friendly.
@Clementulus Thus people around here pass around this gardening meme about pulling the plants to hang them in a garage - which certainly can work, a little overboard though!
@Clementulus Perhaps the fungus doesn't know which way's "up!" Yes, I've seen grow towers like this. I do pretty well avoiding fungus on in-ground tomatoes by using drip irrigation - but with in-ground comes the downside of not being able to move the plants when weather changes.