I think that leaf is dying from old age.

Thank you ! Unfortunately that one has now fallen off, and new leaves are turning yellow. It seems that something is wrong and is continuing to spread.

Thank you so much for this ! Unfortunately as we're in an apartment in NYC growing it outside is not an option. Do you think it would be possible to replant it with new soil? If so, what kind would you recommend? And at this point would it damage the roots or shock the tree to do so?

With citrus older leave turn yellow and drop. The tree may be dropping that 1 twig. The rest looks good. If you can pull the tree out of the pot without the root ball coming apart check for root rot. If none It probably needs feed and micro nutrients and more light. Stop misting the tree.

Steve, even your trees look better than that).

I don't think you would be satisfied with yours looking like that and I think you would figure out what is up. Mines never looked like that unless they were slowly declining.

If she feeds the tree although the roots are not happy, it will just make things worst. Once those droopy leaves rise and stick straight out, that is a sign it can handle ferilizer.

I am trying to kindly tell her that the leaves are all too droopy, almost lying down, facing dowards, and that is a sure indicator that something is going on with it. Thanks buddy. Hope you are well these days)

Ali, what kind of soil mix did you use again? How long does it take to dry out? How much light is that tree getting and what kind of water are you using? You could always do a good flush of the accumilated salts if that is what is going on. It should be repotted at least once a year in mix with fine particles like peat and less often the more porous and the more the mix holds it's structure.

Thank you again ! I don't recall what kind of soil mix, but it takes about 15 days to dry out. The tree is next to a grow lamp that is on a timer, it is on for 10 hours a day. We use room temperature NYC tap water to water it.

But as you recommend repotting it, I would love to move forward with that. What soil do you recommend I get? And is there anything besides peat that I should mix in? We're in the midst of quarantining here, so my only option is to head to our local Home Depot and get whatever they have available.

Your light needs to be on for 16 hours a day. If you have a ceiling fan running that would help draw water from the leave then roots. That light in the picture is not enough. If that is the only light your tree is hungry for energy and is sheading leaves to conserve energy.

Steve

Ali, Steve made a great point!

At least 16 hours of light by now. What kind of light is that and how strong is it? Does it get any sunlight at all in a south facing window?

You could use any good soilless mix you find there, but youwould have to gauge how fast it dries and whether or not it's good for the environment you have it in.

Options

You could use a clay pot with a good soilless mix. Miracle grow will work if you add more perlite to it, or even bark mulch, pine that is.

You could use straight 'pine bark' or 'hemlock mulch with added lime. That would be very porous.

You could use the mulch with added perlite even more porous.

You could use mulch mixes with peat and perlite.

As you can see, there are options, just become creative with a mix that does not hold perched water and that can rot or suffocate your roots. In your situation you most likely need a mix that is very porous and that dries out evenly and quickly like within a couple of days which I likje ro wthin at least a week. )

I wish everyone that grew citrus in containers could understand the concept or how water behaves in planted containers and how to make mixes work best for their trees and grower. There is plenty to learn at the container forum if you ever wanted to know more)

While you stay safe, here is something you might enjoy reading)

https://www.gardenweb.com/discussions/5894651/container-soils-water-movement-and-retention-4-11-20#n=14