.There is no nutritional value in Al's gritty mix and you must feed the tree every time you water it. Are the roots warm or are the pots on a slab of cold concrete. everything else sounds good to me. Spider mites do very well in your kind of set up. Treat with Neem oil and Rotenone per instructions. This will eliminate all pests. Can you build a lean-to greenhouse. My zone is similar to yours and my trees are outside, in ground. and doing much better than my containerize trees.

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Top view of citrus green house

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Main view

If you have room this is the best way to go. Plant them in the ground and you will get a LOT of fruit.

You can build yours so that it is attractive and an addition to your place.

I would use a digital meat thermometer and see what temperature the roots are. A temp below 55f and the roots cant function to keep the leaves hydrated and they fall off. Just because the room they are in is 75f doesn't mean the roots are that warm. Also terra cotta pots will cool the roots through evaporation. Jack

Fertilizing once a week is fine...in fact, that's how I fertilize my trees in the Gritty Mix and the 5-1-1. You might also like to dress your pots with some Osmocote or other slow-release fertilizer.

Josh

Thanks for all of the advice so far. Poncirusguy, your lean-to is VERY impressive, however, impractical for my means. I only have one citrus plant, and building on my property, at this point in time, is not possible. But I understand that you are focusing on the roots of my plant not being happy and warm. This year, I managed to prevent any insect or critter infestation; I dealt with aphids last winter - what a nightmare! This year, everything appears to be bug-free.

Jack - you suggested addressing cold roots as well. My tree is in a plastic pot, in a room on the second floor of a house. I keep the tree elevated off the floor in a plant stand so that there is no chance of it sitting in water.

I have yet to take a temperature reading on the roots, but if there are in the 50 degree range, how would you suggest I raise the temperature? I've heard of wrapping Christams lights around the pot to raise the temp; any thoughts on this? Do you think I should rinse the roots and medium of undissoved salts with dilluted vinegar? Has anyone done this before? If so, what ratio of water to vinegar? White vinegar or apple cidar?

I haven't had any more leaf or fruit drop for two days, but I haven't seen any improvement either. Thanks for the help, My tree an dI really do appreciate it!

I flushed my roots with about 5 gallons of clean water every 3 months. I do this in my basement by soaking the entire pot under water for 20 minutes then flushing another 2 gallons of clean water. I spray the foliage with 1/2 strength 3-1-2 ratio fertilizer. I do not fertilize the roots unless I have an aggressive growth period.

After soaking and flushing the root mass I pull the excess water out with a vacuum chamber under the trees container and use a vacuum chamber. It is very easy.

Use a coffee can with a 1+ inch hole in the side as shone. The 2 tangerine trees are from seed and are 1 year old.

Steve

Update!
So my I scoured other postings and found Mike's advice for adding vinegar to water when watering citrus. Before doing so I tested my water and the differing variations (tap alone, filtered alone, filtered + fertilizer, filtered + fertilizer + vinegar) for pH and hardness. My normal tap is neutral at 7. Fileted through the dehumidifier it is slightly more acidic at 6ish. So I tried one watering of the vinegar and fertilizer, and yes it certainly made my healthy leaves a deeper green, it did not resolve the leaf curl. In fact it got worse. I determined that this was not due to a vitamin deficiency, as no color is leaving the leaves. The leaves start by curling on both sides inward, then hardening from the outside tip inward, until it falls off the tree, felling hard and lacking moisture. I've lost probably 8-10 leaves in the last 2 weeks. I haven't watered in those two weeks. So I dug deep into the gritty mix and found that it was still wet down there, not just moist, but WET! I don't get it, this is what I was trying to avoid by switching over to the gritty mix. I have 10 drainage holes in the bottom of the plastic pot and water drains freely when the tree is watered. I rolled my pot over and gently nudged my tree out to confirm my suspicions - yep some mild root rot!. GRRRR!
Needless to say I am disappointed. I had gone from watering the tree once a week with the 9-3-6 fertilizer which gave my tree blossoms, new leaf growth, even tiny fruit production, to depressing leaf drop no better than if I had left the tree in MG potting soil.
I have the Gritty mix laying out so it can dry a bit, but I am hesitant to put my tree back into it. Any suggestions from anyone who has been very successful with the gritty mix? Should I add more granite to it? I'm thinking adding more of the Fir bark fines will only hold more moisture in the medium. I'm also thinking about giving the tree's root ball a trimming, not completely bonsai, but to allow some air in between the roots that have grown very close together.
I'll post pictures.

Curling leaves

Leaf curl - on tree

Root ball
Has anyone else had the experience of the Gritty mix holding too much water? Any suggestions for remedying this would be greatly welcomed!!

YES I have an answer to your wet wet wet wet problem. It its pictured in my last entry. It REALLY REALLY REALLY works.

Vacuum cleaner citrus water sucker system.

Steve

Ok Steve, I'm intrigued by your vacuum system, but you are going to have to explain a bit more clearly to me about your set up - I'm definitely not an engineer here! lol
From what I can see from your pic, it looks like you have your tree sitting on top of a 5 gallon paint container, with lid ?!?! And the paint bucket has a hole cut into the side with a vacuum hose + vacuum attached to the side. Your description mentioned a coffee can, but I cannot find that in your picture. I'm guessing you have openings between the tree's pot and the paint bucket, but they would have to be air tight for the vacuum to be effective. How do you manage that? And it looks like you are using soil as your planting medium; are you sucking a good amount of the soil from the pot into the paint bucket? Lastly, what do you have preventing water or debris from entering the vacuum hose? The last thing I need is breaking my vacuum in addition to having a unhealthy Valencia on my hands.

The tree to the left in side the other 5 gallon is getting soaked with water and then I will flush another 5 gallons through the tree. That is my soak-er flusher system. I do that half way through cold indoor season. After the soil is flushed it goes on top of the Kilz paint bucket. The buckets with the trees have about 300 drain holes about 1/16+ inches diameter. The dirt doesn't get pulled through holes that small. The top of the Kilz bucket fits snug against the bottom of the tree bucket. The hole in the Kilz bucket is high above the pool level of the water in the bottom. Last I hold the hose so it is pointing down and it will collect little to no water. You can also place the hole at a point under where there are no holes in the pot. Not only do you get rid of extra water but you pull fresh oxygen into the roots. Let the tree sit for a while to drip dry before the vacuum so a lot of the water has drained.

The trees are now set up in the grow box set up to take a vacuum. I hit each tree every day with a 10 second suck to aerate the roots. I will not flush the trees until they go outside in April.

When I am purging the water I will use many 30 second blast with time between so I don't air dry some more exposed roots.

Steve

This is the box the plants are sitting in in the picture above showing the vacuum chambers with the hose hole. This is befor their soak and the vacuum chambers are not set up yet.

Steve