WLD:

1. Leaf get hot, need water
2. Roots cool, not move water fast enough for leaves
3. leaf dies

The most common short answer is an imbalance with light and temps. Too much light and cold roots=severe leaf loss. Too warm and too little light=leaf loss. Ambient temps, humidity, and a host of other factors can affect this, and you will find people who defy this general rule, especially in ground or greenhouse applications, but for pots indoors this seems to be the best explanation.

Most pots are 10-15 degrees F cooler than ambient temps indoors, especially if they are shaded. You noted that the surface of your pot gets to 120 in the sunlight, but you might be surprised by how cool it can be when there is no sun on it. That is why I warned you about what might happen if you shade the pot and do not do anything else.

People here have done a lot of good work to explain this, and I have read nearly all of it. That is what some free time and a case of OCD can do.

Edit--I must have been typing when the answer above came in. Even better.

The tree's leaves are still getting yellow... And buds are not opening.

I realize I am going to go over some things you probably know, but it might be easier to have a flow chart type list:

1. Did you get a thermometer? What is the temp of the soil? If that is around a stable 70F/21C, we can move to the next, most likely culprit.

2. Do not let the soil get completely dry. Ever. I try to let the mix dry a bit between watering, but I waited one half day too long once, and my tree got mad.

3. In an earlier post, you said you used pine bark as potting mix. Was it aged at all, or fresh? I ask because if it was fresh, the pH could be low (acidic). It is impossible to know for sure without a pH meter, but if you have any left over mix, throw a handful in a container and add water. Add a handful of baking soda. If it fizzes, it is probably acidic. Adding a small amount of lime might help--not lime as in the fruit, but garden lime. I believe it is calcium carbonate, or CaCO3, but if there are any chemistry geeks out there who want to correct me please do. I use Espoma brand, but I doubt that is available in Lithuania. If you mix a little in the top of the potting mix next time you water, that will gradually correct a low pH. Next.

4. Again, back to the pine bark. If it was fresh, it could be immobilizing nitrogen in the mix as it composts in the pot. You might have to add more slow release nitrogen to compensate, or wait until the bark stablilizes. Watch out for root burn. This is a tricky one. Next.

5. I have not re-read your other threads and do not remember your fertilizer regimen, but as I recall, it seemed you had a good fert. You could try foliar feeding. Search that on the forums. If your roots are not happy, foiliar feeding might help. Do not spray in strong sun, or put a wet tree in strong sun. The little water drops act as magnifier lenses and will burn the leaves.

That's all I got. Anyone else?

Good luck,
Eric

No, I did not get a thermometer.

The bark was fresh, from an orchid supplier. I mixed it with peat moss (black).

I fertilize it every two weeks with a citrus fertilizer 6-4-6 NPK + trace elements.

Is it possible that the tree is dropping leaves due to a MAJOR ROOT LOSS, and BEING TAKEN OUT OF THE POT THREE TIMES DURING THREE MONTHS?

Here's the story:
I bought the tree in the middle of January, it was in a 15 cm diameter pot, potted into simple soil.
I put the tree 3 metres away from a window (by the way, I recently read that plants, when being put further than 2 metres away from a window feel like in complete darkness).

The tree started to drop leaves.

I went on the internet for help, I was told that I must IMMEDIATELY repot the tree into bark/moss mix.

At the beginning of February I thought I repotted the plant, but I actually just took the tree out of the original pot, wasn't able to take off any of the original soil of the rootball, so I just put it in the bark/moss mix just the way it was - with the original soil on the rootball.

Then I was told that I must take it out again out of the pot and take off at least some soil off the rootball and point the roots to the walls of the pot, because they grow to the direction they're pointed to.

So about in the beginning of March I tried to do that, and got some soil off of the rootball and put it in the bark/moss mix.

Then I noticed that I can't water it normally, since the bark dries out much faster.

Then I started making plants about taking the plant out of the pot again and get all of the soil off the rootball.

In the beginning of April so it was done - I soaked the rootball, scratched with a chopstick and got all of the original soil off. BUT instead of a 15cm diameter pot full of roots it was left with a rootball smaller than a fist (we're talking about a 40 cm tall tree)

Can the leaf drop be caused by this??? Millet, if you can please let me know what you think. And others, tell me what you think!

The short answer is yes.

Your multiple repots and possibly damaging the remaining roots, along with placing a freshly repotted tree in window that gave you a blazing hot pot where the sun was probably too strong for the weakened roots to adequately supply the leaves are probably hurting your tree.

Until the roots heal, time and good management are all you can do. Part of the issue, I believe, was the multiple threads. As I said, I do not think anyone had a great idea of what was going on with the tree, and there may have been some confusion about what the real problem was.

I have a feeling that no one else wants to respond to this because they, like I, feel your anxiety. They also probably feel that you are about to blame someone for the state of your tree. Bold and ALLCAPS are kind of a turn off, if you want a response. This is not meant as a flame, but . . .

Have you gotten a thermometer?

PS--I still believe that a fist size rootball for a 16 inch tree is not a deal breaker. Not ideal, mind you, but the thing should recover if all else is favorable.

It's my own fault. I should've put it on the windowsill right away, not 3 metres away from it. It wouldn't have dropped the leaves so rapidly and I would've waited untill Spring and repotted it. It's also my fault that I didn't do the repot correctly the first two times.

Is it OK to put a plastic bag over the foliage (I heard people do that to lemon trees and other plants after difficult repottings) and keep it moist?
Maybe I should use a rooting hormone in order for it to grow roots?

Evaldas wrote: -----"I put the tree 3 meters away from a window (by the way, I recently read that plants, when being put further than 2 meters away from a window feel like in complete darkness). "-----

The truth of the above statement depends on what the light requirements are of each individual plant. For example ivy, and many other plants, prefer being in the shade. Citrus trees, like all plants, utilize light to manufacture photosynthates (sugars), which are the tree's food source. This is done in a process called photosynthesis. For citrus, the tree's manufacturing of photosynthates reaches maximum production at only 650 PAR, which is about 1/3 of full sunlight. Light levels above 650 PAR will not produce additional food for the tree. Only through longer photo-periods, not higher photo-periods, can a citrus tree manufacture more food, and thus produce higher levels of growth. To accomplish additional growth, growers need to light their trees for longer periods of time, say from sunset to 10:00 PM, and not higher levels of light.

Therefore, Evaldas's tree setting 3 meters from the window was not " like in complete darkness", and if the tree was receiving only 650 Par of light, the tree would be fine. In Southeast China, the native habitat for citrus, trees grew as under story plants, beneath the shade of the taller trees and vegetation of the area. In large estates of Europe, citrus trees are sometimes stored in "dark" basements for the winter, and seem to do OK.


Lastly, a tree's root system, and a tree's canopy, combine to form a unit. For this unit to preform well, it must be in balance. The output of the root system must equal the requirements of the canopy. When the balance is out of order, as is now the case with Evaldas's tree, this creates a problem. Do to the large root loss of Evaldas's tree, the present root system cannot fill the requirements needed by the canopy. This strain on the root system can be reduced several ways: reducing the size of the canopy, lowering the direct sunlight on the foliage, limiting the transpiration rate, maintaining good soil moisture, and providing strong root growth by keeping the medium at the optimum root growth temperature. As this is not my tree, and as I have never seen this tree, and due to the present health of the tree, I feel comfortable only to make general recommendations, but I am hesitant to make any direct recommendations. The best of luck to this tree and it owner. - (Millet (995-)

Thanks for the advice. I pruned the tree, to make the canopy smaller, and covered it with a big piece of gauze, to protect from too hot sun.
But now I think it's in a too big pot, I bought it in a 15 cm diameter pot, and now it's in a 17 cm diameter, but with a much lower amount of roots than it had in the 15cm diameter pot...

Millet wrote:

Evaldas wrote: -----"I put the tree 3 meters away from a window (by the way, I recently read that plants, when being put further than 2 meters away from a window feel like in complete darkness). "----- The truth of the above statement depends on what the light requirements are of each individual plant. <...>

Well, I read about this in orchid care book .

And another (a bit off topic) question:
There's this Portuguese orchid nursery that sells the most beautiful dwarf citrus plants in Lithuania. The leaves are very dark green, shiny and all that stuff (look in the "Pruning" section of the website that I put lower in this post). They claim that they grow their trees in pine bark and peat moss mix 50:50 (here it is ). Would it be a good idea to repot such tree into a 50:50 bark/peat moss mix? Because I might be too weak resist not buying one little tree from that nursery
And people suggest planting citruses into a 4:1 or 3:1 bark/moss mix, but not 1:1. Would it be bad?

A 50:50 mix could be fine. Actually, any mix that provided good drainage and high medium aeration, should work well for citrus. - Millet (994-)

Sorry if you think I'm going way off topic now, but is there any reason why citrus nurseries wouldn't export their trees to colder climate countries (like Lithuania, Poland, Sweden etc.) in summer months?

...

There is only three considerations to explain the problem with the above pictured tree. The tree is either not getting enough water, the root system is damaged, or the medium has compressed to the point that it no longer contains enough air porosity to be able to absorb water (without root zone oxygen roots cannot absorb liquids even in a moist medium). If this is the tree that the entire root ball was transfered intac into a larger container, and the surrounding empty area of the container filled in with chips, any water applied could simply be running down the sides of the root ball and out the drain holes. No matter what the situation, if this was my tree, I would slip the tree out of the container to observe the medium and roots for any damage, and if the roots and medium proved to be OK, I would soak the tree over night in a larger container filled enough water to cover the entire ball of roots - Millet (971-)