What is the environment they are living in now? Is it a sunny window? It is best if you can slowly introduce them to lower levels of light by putting them in a shaded spot first. You could be experiencing something called "winter Leaf drop" This happens mostly when the trees are placed by a sunny window and the roots arent warm enough to keep them active allowing cooling of the leaves as the sun heats them up. Trying to keep the root zone above 55F seems to be a good rule of thumb.
If the trees get a lot of light they need warm temps, if they receive low light they need to be cool.

Mike

Thanks Mike for those suggestions.

As for me, being a New Englander that here,I must bring mine in at the end of every fall.

For my trees, it all depends on what kind of environment I am going to subject/expose them to when they come in.

For ALL, they are receiving much less direct sun by the time they come in. It seems that by getting just 3-4 hours of direct sun outdoors by teh time fall starts, they manage just fine indoors with a very bright lit room or sunny windows.

For some, I bring them in when the days are still warmn to get them use to a warm sunny window or my warm sunny greenhouse by the end of fall.

For others, I bring them in when after they have been subjected to much cooler conditions outside for at least a week or two before I bring them into my cool sunny room.

For others still, I bring these in when the outside temps match the indoor temps at my work or other plant room, that being in the average 60's.

By doing this, I seem to prevent any leaf drop and a weakened state that makes them susecptable to pest too.

In short, try and bring them in when temps just about match the enviroment indoors and try and match the light levels as much as possible.

As Mike said, low light levels cooler environment.
Higher light levels the warmer the room should be. Above 55 degrees at least.

Mike

Great explanations and observations, Mike and Mike! ;-)
You guys nailed it.

Josh

Tanks,
something else you can try is using slightly warm water when you water your trees.
This will raise the temps in the root-zone, and will also help flush excess salts.

Josh

Does using rain or tap water have an effect, my tap water is (supposed) to be about 7.2 anyway, but I was thinking about contributing factors with mine and I have tended to use tapwater recently.

Regards
Nick

Rain water is best.
I use tap water most of the year, however, without issue.
I often add white vinegar to my fertilizer mix to lower the pH while the nutrients
are being absorbed.

Josh