Your tree actually does not look too bad. It may continue losing leaves for a while and it will take a while, maybe not until spring, for it to recover.

Moisture meters can be misleading and you are better off digging into the soil a couple of inches with your fingers to see if it feels moist. If moist, don't water. If dry, then water.

You write that the foliage gets 5 hours of good sunlight. Is the container it self also setting in the direct sun and getting the same 5 hours of sunlight? If the foliage is warm and sunny, the container should be warm and sunny. Every grower that is growing a container citrus, should (MUST) have a soil thermometer.

No, Silica, the container actually sits beneath the sill. The tree is just tall enough that the leaves and branches get light. I Should I elevate the whole plant or perhaps put a grow light on the soil. Also, any tips for warming the soil?

Thanks everyone for your help! I will be a citrus grower yet.

You can warm the soil by raising the pot and/or placing a seed starting heat mat underneath it. I use a digital kitchen thermometer like this to check soil temp. : https://www.amazon.com/gp/product/B00004XSC5/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

WLD

New Zealand lemonade on US897 has lost 2/3 of its leaves

Fukushu kumquat on C35 lost 1/3 of its leaves.

Steve

Thanks everyone.

I'm just going to watch it closely and leave it alone for a time. I put it on a table so that the pot gets some lights too. I don't want to repot it again, as 3 times in 8 weeks has got to be too hard on it. Hopefully, getting all of them--I have a calamondin orange and key lime--outside will fix some things. BTW, the key lime looks terrible. Nearly all of the leaves have fallen off. It came yellowed and brittle, so I don't think I'm at fault for that one. The orange is doing great.

I look forward to learning more.

if your tree is getting over at least 12 hours of direct sunlight or strong light, then the roots should be warmed to 70 at least.

if less that 12, then the room temps should be just fine and in fact even colder than that. I would say low to mid fifties to low 60's.You should not have to worry about soil temps being cooled if you are not providing hours of sunlight or artificial light.

I never let the roots of my soil get warmer than 60 degrees when my trees do not get at least 12 hours of direct sunlight and or artificial light and they do awesome. Once the temps in any room rise above 65, I get WLD.

Have you considered another possibility of leaf drop? I did not have time to read up thread. Sorry.

Myermike_1micha,
I elevated the tree so that the whole plant is getting light. However, I also assume think maybe the humidity level has something to do with it. The temps in southern VA Zone 8a, plummeted about 3 weeks ago, and we started using the heater more. A few days later the leaf drop began. So, Im thinking that may be a big part of it. No other signs of disease or pests.

I doubt the heater is a problem, unless it is a forced air heat system, and blowing on the tree. I would add if the tree's foliage is warm enough so that the leaves require transpiration to cool, then the root system must be warm enough to supply the water needed, whether it is in the direct sun light 12 hours , 10 hours or 6 hours. Hot leaves require transpiration to cool themselves, and if the soil is too cool the root system cannot supply the water, or enough water depending on the root temperature, to cool the leaves. Therefore, the plant has no other option then to drop it leaves. If the tree is located in an area without direct sunlight, then one has much more leeway with the temperature of root zone,

No WLD on either of my 2 in ground outside citrus with soil temperature below 50F.

Fukushu not photograph-able but in good shape after deep freeze going as low as -7 outside. The Fukushu had a 75 watt light bulb heater and the NZL had a 350 watt ceramic heater. Fukushu is fully dormant while the NZL is in active growth with flower buds coming on.

Steve

Steve, temperature of the roots, nor the temperature of the foliage is the deciding factor for WLD. It is the ratio (balance) between the two. That is why trees setting in front of a north facing window, have a lot less WLD then trees setting in front of a south facing window.

Silica I realize that but my trees outside are in ground at a maximum root temperature of 50F but get some direct sunlight on the leaves in a warm glass enclosed cubical. That is cold roots in a south facing window but outside. Perhaps an "unlimited root-mass" outside makes a difference in this kind of cold.

Steve

Thanks for all of your help everyone. I think I've done everything I can/will do for now. It's in the sunniest window in the house. Its been fertilized, and I think it's in a planting medium that will do. It's not Al's gritty mix, which apparently is just this side of the mix used to grow the Garden of Eden, but it's organic and seems to drain quickly. The tree has produced a few flowers. I don't know if that's good or bad or portentous, but it did. So I'm just going to enjoy the sent, and hope it survives until March.

On another note, we have some warm days in the forecast mid 60s. I want to put the trees on the porch, but the temp is supposed to drop again and I'd need to bring them back in. Is it good to move them in and outdoors frequently if I'm not "hardening them off." Will that cause some sort of shock and mess up the one orange tree that appears to be flourishing?

Silica, what explains the situation that I explained? As soon as the temps in my three season porch which gets lot's of sunlight, but not nearly enough of 12 hours, the leaves will drop like flies if I let the room warm above 60 degrees? if kept very cold, they do awesome. Could there be another reason why this happens?

If I bring them upstairs in my warm sunny plant room with a skylight and south facing windows, they will drop leaves and branches in the winter because of very warm temps I have to lower the temps in there to below 60 degrees to stop leaf drop.

Is this all in my head? Or do you have a good explanation for it?

Thank you)

Mike

What's the temperature of the root ball? Stick you're kitchen thermometer in it. It is, in part, the difference in temperature between the root ball and ambient that contributes to leaf drop. You can have a 20C ambient room with a 13C root ball.

This article you may find interesting (translated from a German original): http://steffenreichel.homepage.t-online.de/Citrus/WLD.html

My conditions? 14-15C root ball, 21+C ambient (indoors), southern floor-ceiling window w/ overhang, 45.6degrees north and a supplementary 50watt LED grow light. Flush with growth and minimal leaf drop.

Meyermike, Cool roots and cool foliage is fine, no leaf drop. Warm roots and warm foliage is fine, no leaf drop. Cool roots and warm leave is not good, leaf drop, Mike do you own a soil thermometer so that you can check the temperature of the tree's root zone?

what about warm roots cool leaves?

Warm roots and cool leaves fine - no leaf drop.