Yes your juniper would be better outside. It would like to get some rest and go dormant. It would need to be protected in some manner. The simplest way to protect the roots is to the bury the pot in the ground. Likewise mulch could be used around the pot up to the lowest branches. You must also watch for cold drying winds that could damage the foliage.Watering is a little tricky if your weather is as varying as you note. Too much water can cause root rot. However the tree can not be allowed to dry out. Snow actually helps by acting as an insulator and providing water during thaws.
You can acclimate by bringing the tree out on a porch or similar a few hours during the day increasing the duration each day for about a week. Shouldn't have that much problems acclimating as even in nature in gets cold quite fast. The increased exposure to sunlight is more of a concern but since it is a fall/winter sun it should not be a problem.
Welcome to the art of bonsai. And good luck with your tree. If you have any other concerns or need clarification, just ask.

You can over-winter it in an unheated, attached garage if you have one. All my temperate trees over-winter there. Burying it on the north side of a heated building against the foundation is also a good way to over-winter.

It doesn't matter if the soil freezes solid unless it's for an extended period (too long and the top will dry out) or temps actually drop below killing lows. It's not the water in the soil or inter-cellular water (free water between cells) freezing that would kill your plant outright; it's the intra-cellular water freezing (water inside of cells) when temps drop low enough that kills roots. Also, not all roots on the same plant are equally hardy. The finest roots are least resistant to cold, and the colder it gets, the larger are the roots killed by killing low temps. Ideally, you would keep your root temps above 28* or so, even though killing lows for the plant proper might be much lower.

Al

That's the advice I have been looking for! Thank you both very much. We'll see if it survives the winter.

Al
Do you bring your conifers in to the garage also? I bring my deciduous trees in but not my conifers.It has been my understanding that the evergreens would benefit from the light/ photosynthesis. I realize that this is very limited during dormancy.However i thought it detrimental to not provide light. Please share your thoughts.

Very controversial! But I think if you have either dug the pot well into the ground, or else protected it well with a large mulched container, etc. and depending on where you live (the real arctic vs N. Jersey) and what you're growing, you could leave them out. It depends! Everything depends :-)!

This post was edited by moochinka on Sun, Dec 7, 14 at 15:28

To a very large degree as temperatures fall, the rate of photosynthesis is determined by temperature. When you're talking about temperatures low enough to provide the chilling it takes to release a plant from dormancy and subsequently keep it quiescent, you're talking about very minimal photosynthetic activity.

I actually have 3 J procumbens and a Shimpaku that overwintered outdoors on the north side of my garage during the worst (coldest) winter I remember since maybe in the 60s when I was a kid. They all survived with no trouble (I was amazed). I actually did think about this very issue in the spring after they resumed growth and my other plants were back on the benches. I looked very carefully at the branch tips and could see no difference in the node spacing, which I would think would be a major concern.

Don't forget that significant damage can occur during periods of low temps and high light. I think I would probably say that some light might be of some advantage, but I think it's a very insignificant consideration if you're talking about trees stored at or below about 45*.

Al

Thanks Al
I asked because I have a young white pine (parviflora) I would like to protect. Would be easier to bring it inside with my deciduous trees. Also meant to ask whats the reasoning behind the 'north' side.

I also will have to do more research on High light/ low temp photosynthesis subject. Sounds interesting. I think you touched on this in the other juniper post. Will do my own due diligence,but if you have a link or other reference on this subject, it would be appreciated.

The north side because in the spring when things warm up, it's tempting to bring out your trees from protection. Except it suddenly gets cold again, and once buds begin to grow and open, the tree can die from exposure, whereas leaving it in the cold to begin with gives it more chance to not come out of dormancy until all frost has passed (depending on where you live). White pine can take cold temps, certainly in NJ and it would be best if you left in outside.

It's actually more important for deciduous material than evergreens because deciduous plants enter dormancy and then pass into a period of quiescence, during which any prolonged exposure to temps much above 42* can initiate growth. Pots & soil are passive solar collectors, so even if the air temp is 0*, if there is sun on the pot or soil the soil temp in the pot can rise above 42* during the day. During winter thaws, this can be a serious problem, because once the plant is stimulated to growth, the plant is significantly less able to resist chill injury when temps drop.

Also, sun tends to increase transpirational water loss from foliage, which can be a serious issue if water in the soil is unavailable as ice. Plants on the north side of buildings are shielded from the sun, so the added transpirational water loss and passive solar gain (soil temps) are non issues.

Actually, I prefer that my evergreens over-winter in the garage. Foliage never dries out, and since the temperature rarely drops much below 30* (unless someone forgets to close the OH door at night) I never lose even the finer roots.

Al