Though all my gingers are outside, in the landscape, gingers in general like lots of water and lots of fertilizer. That being said, they will still do quite well with the lack of either or both. They are also very vigorous growers. I would remove your plant from its pot (the whole root-ball should come out pretty easily) and see if the plant is getting root-bound. If so, re-pot it in the spring in a pot twice the size it is in. Use potting mix that drains well but still retains water a bit more than the average mix. A commercial potting mix is fine as a base, but to every gallon of that I would add a large handful of milled sphagnum moss to retain that additional water.
I don't have any variegated ones, so I don't know about sun-tolerance of the one you have. All mine get full sun for 6-8 hours (spring/summer).
