Photos always help! But we can make some assumptions here. The tree's indoors in Zone 3, or it would be frozen solid and dead. That's assumption 1. :-) It's difficult to impossible to get a citrus to bear indoors over the winter, so that's unsurprising, and it's also unsurprising that they'd drop leaves and not perform their best.

A few things you don't have to do are the powdered eggshells (they do work, eventually, over a very long period of time, in some circumstances...but not here. There are faster calcium sources if you require one). The fan is nice if you have stagnant air in your home, but not strictly required. However, if it makes you feel better, by all means, keep it. And the shells certainly didn't hurt anything.

For watering, I wouldn't let it go dry, but don't allow it to remain sodden, either. For winter, "slightly damp" is fine, and you can let the top few inches dry pretty thoroughly before watering again.

We'll probably also ask what kind of lighting you have it in. A window? Southern? Southeastern? Do you have additional electric light on it? LED? What wattage and for how long per day? It'll give us some idea of what to expect in terms of leaf maintenance and growth. Citrus really do require quite a lot of light or they'll drop leaves.

The "white spots" and "rust" you describe are what we'd want photos of. Probably from a distance, as well as a good close-up, if you can get one.

First, a couple questions, then a couple observations:

- when you say you added peat to all purpose potting soil, what kind of potting soil did you use? What was the makeup? You can usually find that on the side of the bag.

-when you say 50% bigger pot, what was the original pot size, and what was the size of the new pot? What kind of pot are you using? Do you have it on a drainage tray, or what kind of drainage does it have?

-As you were watering, did you ever feel the soil to see how wet it was?

-Do you just have the tree under lights or is it near a window, and what kind?

-what is the temperature near the tree, and how close to a heat source is it. I'd hesitate to use a fan for air circulation in winter so close to the tree unless you have humidity problems as you risk further drying it out.

-Can you post a photo? It would be easier to see a photo of the whole tree and the leaves.

And for a few observations:

- You mention you were watering on a schedule and then started watering daily. This is a pretty solid way to kill any houseplant. The old advice of watering on a schedule has, in my experience, always been some pretty rotten advice and usually leads to rotten roots and dead plants with some exception. With most plants you really should check on a schedule and water when needed. How you check is really up to you, in smaller pots if you stick a finger in the soil and feel moisture lower down, you don't need to water. In larger pots you want to use a skewer stuck down in the soil and removed - if it's wet don't water - or a moisture meter (although with these you kind of have to self-calibrate to figure out what your meter reads as dry as they are not always accurate). I've found with my own citrus that there are some weeks in summer where I'm watering once every 5 days, and others where I don't need to water until 10-14 days have passed.

-trees can flower from stress, and often if they do this, they won't hold on to fruit.

- roots need oxygen, and can drown, so if your mix is too tight or stays too wet you can have all kinds of problems.

FWIW, there is no such thing as an "indoor" lemon tree :-) While many citrus types can be grown indoors under the right conditions (and produce fruit), they are happiest outside during the warmer months.

And if grown in a container, it will also need routine fertilization. Feel free to add the eggshells if you want but don't mistake them for a proper fertilizer - they add virtually nothing.

These "indoor citrus trees" are meant to be grown in an orangerie or a greenhouse.

Nathalie, I'm sorry but you're in for a lot of heartbreak with your tree. They are programmed to be grown outside. They can tolerate being inside for the winter, but even then they will experience all kinds of issues.

I gave up on my citrus trees (in zone 6) after a couple of winters of trying to keep them alive. One day I just took them down to the dump because it was a never-ending struggle. They looked great on the patio in the summer though, so I can understand the appeal.

I recommend you replace it with an indoor house plant that will love you back.

What caught my attention is: I give it 2 to 3 tbsp of 10.10.10 food every week and spread it on the outside, never close to trunk

That is way too much fertilizer and that too you are adding raw undiluted fertilizer directly to soil. Which 10:10:10 food it is? If it is synthetic water soluble fertilizer then 1 tbsp per gallon of water per week will be about maximum you can use during peak growing season. During winter when growth is very slow you need cut back the fertilizer a lot.

In containers it is not a good idea to add raw fertilizer (assuming it is water soluble synthetic fertilizer). It can quickly lead to salt accumulation and rapid decline of plant health. In your case, the saving grace has been that you added it to the edge of the pot.

My immediate suggestion would be to flush the soil really well with clean water. Fertilize very lightly starting with the next watering. Check the label and follow that properly. Often bulk fertilizers do not provide dilution rates for container plants. Instead they may say use a cup for so many square feet. Translating that to a container is not worthwhile.

Jojo. Hi and hugs!!! Good advice and hoping all is well these days. Maybe we can instant message soon)

Tropico, hopefully things are ok for you too. Good advice as always.

Nathalie,

Here's a fun read -- pretty basic stuff but still good.

https://www.gardenista.com/posts/5-secrets-tips-grow-indoor-lemon-tree/

Thanks

Bonsai, that's great! I'm glad someone is having success indoor! Do you mind posting some pics of your trees? I'm curious what your setup is.

I've posted some in the colors flowers and plants february 2021 forum. I can repost them here if you'd like. It has a learning curve, (and to be honest I moved to citrus slowly, started with a tropical rhyzomatus angel wing begonia (and now I have spent the last year trying to figure out how to get it to slow growth), moved to orchids, then to the citrus once I had kind of dialed in where in the house they would grow best. The begonia was a really good indicator, if you can get them to grow fast and big, then you should have success with the citrus. At least in my area they're pretty cheap if you want to get them small.

@bonsai_citrus_and_indoor_gardening

Thanks for that. Yeah, if I can make full sun plants blossom in Pennsylvania in January and February indoors, others can have their citrus trees. It's just not easy. But anything that can be done outdoors can be done indoors, just often with more trouble and effort. And electricity...

Electricty!! Yes, lots of that..lol