Hi Laura and Vladimer, I am having the same problem with my Fukushu Kumquat that I have had a long time. It is the mother of Steve's 2 plants I gave him. They were from seeds from her fruit. That and my Key Lime I grew from seed suddenly shed most of their leaves the past couple days. The key lime does this every year but recovers in the spring. I don't remember the Fukushu losing all its leaves at once before but several years ago I had a Meiwa do that. It did not recover. I think I watered them well when the weather was warm and sunny. All of a sudden there just has not been hardly any sunny days and they are not drying out fast enough I think. My other trees are dropping a few leaves, but nothing like these two, fortunately. I have moved the Kumquat where it gets a little more light and closer to a fan. Like yours, my soil (511) is not sopping wet just damp. The top 2 inches are actually quite dry. It doesn't seem like it would be enough moisture to cause root rot, and I don't think the top inches are too dry. The Fukushu has a lot of fruit which I have now picked off. It hadn't started to set fruit until September. Maybe that was too late. I hope it makes it to spring. The black citrus aphids attack on the Ponkan is subsiding but now two other trees are being attacked by green ones. I am neeming them and alternating with soap sprays but they are hard to keep up with. All my trees were doing so well and putting out new leaves and blooms all Fall and until the last week or so, but once all the long dark days came I think they can not support all that new growth and flowers and are shedding leaves to compensate for the low light levels. It begins to get dark at 3 pm now. It is very hard to watch them shed leaves like that. I am wondering if it might be better to somehow not let them keep growing so much into late fall. Maybe all that new growth has not had time to harden off and all that new fruit and no sun is draining the trees of much of their energy. Maybe we should reduce fertilizing earlier to give the new growth time to harden off and also to discourage the trees from forming new fruit so late in the season. My trees closest to the "glass" are not losing leaves, maybe because they get more light. It is the trees in the interior that seem to be losing the most leaves. The way my greenhouse roof is situated it really doen't take in much sun in the winter but I didn't have much choice without putting it in a funny angle on the lot. My Fukushu was sort of buried under the branches of some of my taller trees. The key lime is in the corner on the north side of the greenhouse but near the "glass". Maybe it needs warmer temperatures? At least the days will be getting longer now. I hope we will get more sunny days. It has been so dark I need to turn my lights on in my house during the day to see. Funny that our citrus friends way up north in Canada seem to have brighter and more sunny days than we do. I would not have known that. I hope our trees adjust soon and can hang on until they can go out again in the spring. Cory

First I'm not a container grower....probably would kill everything if I tried...but aren't those leaves displaying that Christmas tree pattern with darkest green around the veins and midrib? Would that be magnesium deficiency? Also wondering if the soil may be accumulating salts if it hasn't been flushed now and then? I understand that's a new pot but wondering if you water it enough now and then to get a good flow of water through the soil to dissolve and flush through any excess minerals/salts that would accumulate from evaporation. Fish tanks and potted citrus accumulate salts/minerals since the water evaporates and leaves behind anything that was dissolved in the water. Again, not a container expert but perhaps this will offer some other options for the experts here to discuss. Perhaps it's time to leave well enough alone if you are getting flower buds....but don't some trees flower when they are under stress?

In sandy and calcareous soils, foliar applied fertilizers are 4 to 20 times more effective when compared with soil applied fertilizers. (Lingle & Holmberg, 1956.) https://citrusagents.ifas.ufl.edu/archived_presentations/fall_prg2010/Citrus%20Agents%20Web%20Site%20-%20Nutritional.pdf Citrus foliar fertilization has been an industry standard practice in citrus groves for over 50 years. https://crec.ifas.ufl.edu/extension/trade_journals/2014/2014_April_citriculture.pdf Where soil PH is too high or too low, resulting in 'lock up' of nutrients (frequently micronutrients) in the soil, foliar application of those nutrients will ensure rapid response in the trees and prevent growth from being restricted. Effect of irrigation water acidification and soil pH on citrus nutrient availability https://citrusresearch.ifas.ufl.edu/wp-content/uploads/2019/09/7.-Morgan-Expo-2019.pdf Four winds growers sells over 50 varieties of citrus nationwide. Here is what they say about misting, "In winter months, heated rooms may need additional humidity. Placing the pot on pebbles in a saucer will elevate the tree above the drainage area, and improve airflow and humidity for citrus. Misting citrus foliage with a simple spray bottle is another way to help citrus cope with insufficient indoor humidity in winter." If you have new leaves and new shoots it is really beneficial to mist those. Because of the VPD they loose moisture much faster than mature leaves. Flowers are also very susceptible to losing moisture and misting can help them set fruit.

Thanks for the input. My assumption up to this point is that pruning the damaged growth induced growing during a time when it wasn't actively growing due to the low light levels, hence the gigantic leaves. I've been back and forth on removing them now because the tree is covered in new growth and I wasn't sure if removing the large leaves closer to the top of the tree would encourage growth lower down. At the nursery someone pruned it back pretty severely, causing a rather large hole in the canopy on one side. I've been doing what I can to try to encourage growth in this area in the hopes that it will fill back out. (From the right angle it looks like something took a bite out of the tree). At the end of the day though I'm looking for health over appearance.