Well, a little hard to see the sideways photo, but I would suspect a watering issue (either the potting medium is not well draining enough, or, it is becoming hydrophobic, and not absorbing enough water), and not enough light (leaf drop). What potting medium are you using and what additional light source are you providing? Also, are you fertilizing regularly, and if so, with what, and when was the last time you changed your potting mix? It will eventually become exhausted and collapse after a number of years. More quickly if your particles are very fine.

Patty S.

Yes, to add to Patty's good comments, it seems as if I see only a blob of wet soil on the top of your pots...Are you watering in sips..?

If you let any of your plants die just once to the point of wilt, that is a common thing to happen too..

Usually, when trees are weaked, they are susecptable to mites too...I would check for these too....A double wammy can happen at most times this time of the year...

MIke

A common error of indoor plant growers is confusing the air temperature with the root temperature. Your plant seem to be sitting on the floor.. the coolest part of the room. Get a thermometer and check the soil temperature; roots grow in the soil, not in the air. If the soil temperature is too cool, it matters little what attention you give to the plant.

John, I lived in N. Indiana for 10 years. And, although it is butt-cold in the winter there outside (zone 5), inside my house was toasty warm. Even the floors were warm, as we sat on the floor quite a bit watching TV, playing games, playing with the kids, etc. (and being a native S. Californian, I was a wimp when it came to being cold). Plenty warm enough for citrus. Now, unless you've got your citrus in a cold room (insulated, but not necessarily heated), then this is a non-issue. And, this tree certainly looks like it has far more going on than just cool roots. I would say it is a watering issue, & lighting issue, and can't tell for sure, but it's either very dry, or soggy at the bottom. Rorion needs to let us know about how he's watering, what kind of potting medium he has the tree in, and how much light the tree is getting (what light source - N,S,E,W, additional light??). A tree with cool roots will simply not develop flush, but will maintain it's canopy is a suspended state. Just like our citrus here in California during the winter. They don't flush, since it is a little too cool. They don't, however, drop their leaves or look ill. Just static.

Patty S.