Whats going on here?

I have 3 trees atm, which were labeled as Zelkova. I have them all in different mediums. One is in almost 100% catlitter. One has the rootball in the same soil that it came in, blended with some of the dirt around it. The third one has the same soil around the rootball, and the rest a mix of catlitter and sawdust, I gathered the last time I was carving one of my trees, just to test it. I water when they are equally dry. I have them at the same positions right next to eachother. they therefore have the same humidity, light and heat. I took a picture of each of them now, not so good though.
I have not wired. And I have not pruned. Just focused to keep them alive. Here they are.
The one in cat litter and dirt:


The one in pure cat litter around the rootball. Lost 75% of the leaves. 50% of the rest are yellow/brownish. (Pardon the flash)


The one in catlitter/sawdust.


And one more thing, the tree that seems to be still very alive and well, havent produced more than maybe 4 new leaves in 3 weeks.
These days I have them inside. Since there is very cold outside. Mid days its about -5c, and harsh winds. And it will be alot colder.
Elms should as far as I know drop their leaves. But Im useless when it comes to chinese types, crossings between species etc.
Same with my azalea. Its still outside, getting snowed down. Havent lost its leaves, but its a bit discolored here and there.

My guess its the transition. From buying it getting it home, and having a too hot environment. And one has just not given up yet, like the two others.
From what I know, they could already be dead when I bought them also.

Could it be that the kitty litter has broken down and turned into mush around the roots? It could then be nothing but a nasty mess of mush that hold too much water.

Nope, really dont think so, since I use the same type of catlitter for all my trees, and the others loves it. And, I dont know if I wrote it good enough, but there is cat litter in all the pots. And the healthy one is just mixed with a bit dirt. They were also repotted the same day all 3.

Storm , on one of the photos it says "The one in catlitter/sawdust." what do you mean by sawdust ??

A type of mulch after you have carved away pieces of trunk with a dremel. The same thing when cutting planks, but its much finer. It might be the reason for one tree, but the other has 100% cat litter around the rootball.

Storm wrote:A type of mulch after you have carved away pieces of trunk with a dremel. The same thing when cutting planks, but its much finer. It might be the reason for one tree, but the other has 100% cat litter around the rootball.

more than likely , when did you repot them ? and where are they positioned ?

I cant remember when they was repotted. But It was at a bad time. But they looked good for atleast a month after repot. I hardly removed any soil from it, I just checked them, and filled something better draining around it. Its positioned indoors atm, since its so cold outside. In my best lit window.

Storm, if you scratch a piece of bark to reveal the cambium beneath, it should be green. If it is not green, but brown, then that area is certainly dead. Find a thicker branch, and scratch underneath (so you can't see the scar). If everything is green, then your leaves are probably just doing the Autumn thing - turning color and falling off. My Chinese Elms are still outside and one is still putting out new growth as well as having its older leaves turn color and falling off. Some of my Chinese Elms need six to eight weeks of cold before coming indoors. Others stay outside all Winter long, buried in mulch. Your photo of the yellowish-brown leaves (elm) shows buds on the branches which look pretty healthy.
Salut, Todd

I bought one from Brussels in june and its been in the mid 20's F at night. I just bought it inside and it sill has leaves. Not alot of leaves but has about half still on and about 1/3 of those are yellow. I havent done anything to the tree, just sniped a few long sprouts.

First of all, I doubt these are Zelkova. They are probably Chinese elm, Ulmus parvifolia.
I gather you repotted them in the summer or fall? Not a good idea. You should have waited until spring. What's done is done.
DO NOT BRING THEM INDOORS. DESPITE WIDESPREAD BELIEF, ELMS ARE NOT INDOOR TREES. The poor things are trying to go dormant. Leave them outdoors until night temperatures are below freezing. Then put them in a protected COLD location for the winter. They should be where the temperature goes from a little below freezing to not more than 45 F, 7.2 C. They should not be growing new leaves.
I happen to have a corkbark elm prebonsai. Right now, in Zone 5, it is in the ground under a rose cone (a thick Styrofoam protector).
You mentioned sawdust in your soil. Do not use fresh sawdust. As it decomposes it will use up all the nitrogen, leaving none for your plant. Even composted sawdust may be questionable, since it will hold a lot of moisture. Use chopped bark.
Iris

Exactly as Iris has said! Take her advice!
Chinese elms are deciduous trees, so they will go dormant and leaves started falling off.

Storm, what cat litter do you use?