It looks like a root issue, probably the soil gets too dry and the plant is rootbound.

I suspect if you have an indoor heater on a lot the inside air may be rather dry. That is not helping, but is not the main cause of the problems.

Leaves will start folding up like that if the roots aren't able to supply the plant with enough water. I'd consider a bigger container, and possibly mixing in some potting soil specially formulated to retain moisture better.

There could be numerous causes for the tree's dilemma, but the problem is definitely with in the roots, You will not know what the problem is until you pull the tree from the container and examine the root structure.

Gee, I am glad you guys agree with me.

It is dying, alright; you have likely killed it with a massive fertilizer assault.

It's too late now, it's a lost cause.

Thanks for the input all - I pulled the tree from the container and snapped some photos. The roots did seem to be pretty bound, so I tried to untangle the roots from the soil and then repotted. Tomorrow I'll go out and buy a larger pot (~10 gallon) for it. Any suggestions / thoughts based on these photos and observations?

- From the soil, it's not clear to me whether the issue was underwatering or overwatering. The soil was dry at the top, but moist in the middle and bottom.

- I mixed the soil together before I repotted, and didn't soak the pot in water as the soil seemed fairly moist already. The last time I watered the tree was 4 days ago, and the last time before that was 11 days before then.

- To my (completely untrained) eyes and hands, the roots didn't appear to be rotting or soggy anywhere. The tiny roots at the top felt a bit dry.

- On that note, is it okay for those all tiny roots to be exposed *above* the soil? Could that have been part of the problem?

- If you look at the last photo below, you'll see what appears to be larger root growing horizontally... maybe spiraling around in a circle. I couldn't tell exactly what was going on, as it was packed in there pretty tightly. Just felt like this was worth calling out.

- Finally just as a point of clarification the leaves began drying up and falling well before I fertilized

It is pot bound and in needs to be put int a pot once size larger. I still think you should have soaked it because I suspect the soil may have been dry in the interior of the root ball and it would have not done any harm to soak it any way.

It needed WATER, not fertilizer. Every other pic of a Citrus plant posted on this forum as either sick or dying seems to be suffering & dying from severe drought conditions.

Jurasico, you might be right. So much has been said about overwatering that some people might have gone to the other extreme of underwatering.

The important thing is that one must dig down an inch or two and feel the soil to see if it is damp. If is it is damp, don't water. If it is not damp, do not water. Do not rely on an unreliable meter. Rely on your trustworthy sensitive fingers.

Thanks all. What I'm confused by is that the soil seems quite moist to me - when I lifted the plant, basically everywhere except the top 2 inches of soil were damp, including near the center of the rootball. I do use a moisture meter, but I always confirm by feeling the soil that it drags up with it. Over the past month, I have watered the tree less frequently but only because it's stayed damp longer - it almost seems like with less healthy leaves, less of the water I give it is being used...

As a quick update, a few more leaves have begun shrivelling up and it seems all of the large branches are brown. However, when I scratch the trunk, it does appear green underneath.

Vladimir - just to confirm what you mean by "soaking the pot" - do you mean taking the pot and placing it in a tray of water so that it absorbs water from the holes at the bottom (sort of like in this photo)?

ABC putting it in a tray will work although I prefer submersion in a bucket.

or laundry tub or even a bath tub. The tray will not work once the soil is hydrophobic.

Some of the most popular selling, commercially prepared mixes (even those advertised as Citrus or Cacti or Palm), are very peaty. I have found that these soils become extremely hydrophobic over time, especially for those of us who put our plants outdoor and the soils bake in the sun. There may still be damp pockets but there could also be pockets of bone dry soil. Ironically, peaty soils have the reputation of being too wet for too long for Citrus; ironically, these same soils can kill by dehydration.

I’m sorry about your tree. It definitely looks dehydrated to me. I’d try what others have recommended above. Good luck!!

Jurasico - what kind of potting mix would you recommend? As it turns out, the nursery that I purchased this tree from had recommended citrus/cactus/palm mix; I'm now skeptical following your comment...

Jurasico is absolutely correct on cactus mix. It kills

Jurasico is absolutely correct on cactus mix. It kills Is not quite correct. It is not the mix that kills it is the person who does not know how to care for the tree that kills the tree by overwatering it. I have grown my calamondin tree in MG citrus/cactus mix for about 35 years and it is still alive. However, I do not recommend that a novice use it.