Hi, I lived in G. Rapids MN for a while so know where you're coming from :-), but unless you have access to ground somewhere, or a shed... I will comment on what you're doing now though, which is giving it not NEARLY enough light all day long (i.e. 15 hrs/day), and you're watering about 3 times more often than necessary. You said there's new growth, but I find that hard to believe unless your 'watering' consists only of spraying the top of the soil vs actually watering til it runs out the bottom of the pot. And as soon as cold weather comes, watering should be drastically cut back in any case, but as you're also indoors (or the tree is) much less often is still better but I'm not sure how long it'll last without proper dormancy, which is vital to any but tropical or semi-trop trees. I definitely do not endorse fridge growing (and especially not watering while there) because it's very difficult to control elements such as mold, dryness of the foliage, etc., and it doesn't get to go cold gradually as it would outside, nor really cold enough altogether (tho' the freezer is absolutely not the answer).

I just realized you asked about bringing it IN, therefore I guess it's on the balcony, which is a whole other thing (wish you'd have said so!). DO get a much larger container, do stuff mulch material between the container and pot (which would be buried (with a couple of inches of mulch on top) when overnight temps go below 25, though I'd keep it in an open box to protect from wind until then, maybe with some padding for the pot, but don't 'protect' it from going dormant too soon, and allow the foliage to not be covered. As soon as you know temps will go below freezing (prior to above, I guess) make sure it IS well watered that day and then once the soil freezes, don't water at all til the last thaw/freeze is done with (e.g. May), though if it's dry there, you can always put handfuls of snow on top and on warmer days it will be watered naturally.

This post was edited by moochinka on Mon, Sep 22, 14 at 6:21

My junipers are fine outside with mulch over the pots and lower trunks down to about 10F, but when it gets that cold here it may only last a day or two then gets back to 20+. Moochinka has given you good advice.