Hello.
I love citrus and i have 4 different species containerized: Calamondin, mandarin, Meyer lemon and a Buddha's Hand.
The Calamondin and not so much the mandarin started to shed leaves (every day 2-5 leaves) for 1 month now.

The Calamondin is in a 1.5 gallon plastic pot near a window. Right now it is finishing flowering and developing a lot of fruits.
It stays constantly at a temperature of 80-90F day/night and I water it every 2 days with 1,5 liter (0.35 gallon=50ounces) until it starts to drip on the other side.
I don't know why but the lower leaves near the trunk started dropping. I lightly fertilize the tree every week. The earth seems very dry when I water. Because it is so close to the window the pot get's very hot (I insulated it this week to see if that is the cause).
I attached some pictures of the leaves and of the tree.

Am I over watering/ under watering?
Nitrogen deficiency?
Root rot? (they seem to be OK)
Disabled roots because of the heat?

Unless you have very good drainage you are probably overwatering. If you have very chunky media like CHC or chunky pine bark, you basically cannot overwater because the media contains lots of air spaces, however, if you media is mostly peat moss, it is likely you have overwatered.

I have several in containers outdoors--the media is chunky pine bark--like 1 inch chunks and 1/4 peat moss--in summer here it often rains every day for weeks, but my media is chunky pine bark ant they do not have a problem. When it doesn't rain, I water once a week.

Probably I'm over watering. I have watered so much because the top 2 inch are very dry and it has so many baby fruits developing. They need lots of water to grow I have read here.
The drainage isn't so good I believe but the other citrus I have do just fine in the same type of soil.
My opinion is that the water quantity is just fine but that water doesn't let space for air. I'll try and make a new soil mix but is it OK to transplant the tree now?

From looking at your Calamondin, I must say that you have done admirably with your tree. The tree is quite vibrant, healthy looking, and easy to see that it has been given good care. However, due to the present size of your tree, and the small size of the container, that it still remains in, my best assumption is that the tree's root system is becoming root bound. The first sign of a root bound tree, is a medium that becomes dry quickly, even with frequent waterings. If the condition is not corrected, tree growth begins to slows down, followed the tree's general decline. I notice that the leaves you have pictured, which have fallen from the tree, have done so without their petioles (stems) still attached to the leaf blade. When a citrus leaf falls from the tree, and its petiole still remains attached to the branch, it can be caused by certain types of stress to the tree. It is easy to see iif indeed your tree is becoming, or is already is, root bound by slipping your tree from its container and examine its root system to see if the roots have already grown up against the inside of the container walls, and have begun to circle around and around. All in all, you tree still looks healthy enough, but probably needs to be transplanted into a larger container. If transplanting is needed, use a container 4 inches larger than the one it is presently in. Good Luck. Millet (1,250-)

Your Calamondin looks OK. The "lower leaves near the trunk" are the oldest leaves. They have to die one day. Leaves remain about too years then fall.

Sylvain, is correct that citrus leaves that have reached approximately the age of two years old are at, or near, the end of their useful life, and are discarded by the tree. However the old, nearly dead leaves that are discarded from the tree are no longer a dark healthy green color, but are rather dull, and yellowish or yellowish brown, and clearly look worn out. - Millet (1,260-)

Thank you for answering guys. I see that this is forum is very active. So for now on I am here to stay!
Millet, I have changed the pot 2 months ago. The roots are growing fast but they are not rot bound. I checked that when I checked for root rot.

Sylvain, the leaves are not falling from old age because they are falling at a rate of 2-3 every day, more the day after I water it. It's been a month now it has done that. Beside that I saw today that the twigs that lost their leaves are getting yellow also.

This month was very hot here and I can't change the pot's place. Near the window (where I keep it) the pot get's hotter than 100F I believe and the soil get's very fast dry/hot on the window side (on that side the roots didn't grow at all but on the shadowed side they are doing well). So the tree is stressed because of the factors: over watering on the shaded side and high heat on the other side). I have insulated the pot and I'll see what it will do next.

Right now it is starting a new growth flush but only on the tallest branch and I think I am not going to let it grow because it will unbalance the tree and all the new growth have flower buds and I think the tree can't support so many fruits.

Also I don't like the soil but in my crappy country I can't buy moss, CHC or other fancy soil you guys have there.
I try my own recipe but it doesn't get as near as good as what you cand do there.

I'll add more pictures later because I don't have my camera with me.

Following is a description of an experiment by Dr. Carl E. Whitcomb of the University of Oklahoma demonstrating how long the side of a container must be exposed to direct sun in order to reach lethal root temperatures where roots are concentrated inside smooth plastic pots. This study was done with three-gallon containers for the entire growing season. The trees were grown well in full sun, but with the containers protected from the direct rays of the sun, extensive root growth was present against the inside wall of the black, smooth walled containers by September. At that time the trees were removed from the protective environment, carefully labeled and exposed to full sun for 0,15, 30, 60, 120, and 240 minutes, and in various positions beginning at 1:00PM.. Following the various time exposures, the trees were returned to the protective environment for 10 days. The trees were then removed from their containers for root evaluation. Roots of trees exposed to full sun, with the container on the side were dead following exposure of just 15 minutes.

I ran a similar test in Colorado on my trees using a soil thermometer. My test was done in June. After just 11 minutes, the temperature of the medium 1 inch inside the container wall had reached 125 F (51 C). - Millet (1,249-)

Wow. I have fallen in love with this forum.
Nice info. Today I had on the sunny side more than 115F. But insulated it stays at 80F.
The tree look OK for now and I hope that it will not suffer.

I don't think that the experiment is true. All my citrus stayed glued to that hot window for all the summer and they didn't die.

I have managed to take some pictures of the of the roots on the both sides.
Guess witch side is which?

IS IT ROOT BOUND?

Midddle photo shows the sun side of the container. - Millet (1,249-)

That's right. Should I change anything beside insulating the pot?

Insulating the container should work fine. You can also place your containerized tree inside a larger container. This is called pot in pot. Your outside container could be a decorative container, if you would like a nice appearance. I have 100+ different citrus varieties in containers, in my greenhouse. I paint one side of the container white, and leave the other side black. During the summer I turn the white side toward the sun, and during the winter I rotate the containers so that the black side faces the sun. However, a white surface only reduces the temperatures approximately 8 to 12 F, therefore insulating your containers will work better. The best to you and your trees. - Millet (1,249-)

Thank you for the advices.
The best to you also!

Hello again. The Calamondin is still loosing it's leaves even after the heavy insulation. The leaves are dropping with or without their petiole but not before the leaf veins are getting yellow. They are starting to fall from the upper side of the tree. I can see some twig die-back. It is still flowering and I can see some new growth starting now and then.

The clementine mandarin has started loosing it's leaves too. The tips of the leaves get brown or they fall as they are. The three is not over watered but it stayed in a semi dark place for a couple of weeks now. I can say it's more under watered than over watered. I think I am going to cleft graft something else on this three because it gave me in this 5 month I had it problem after problem: not setting no fruit from hundreds of flower, scale infestation, leaf drop, leaf yellowing, new growth falling and now again leaf drop.

I think I am going to change the pot of the calamondin with a bigger one and with this change a part of the root ball soil. Maybe the tree is getting to big for it's pot. Or is it because of the heavy crop? The fruits are not getting bigger than 1 inch diameter.

Here are some pictures.