I think you may be about to be saved by the arrival of Spring when you can begin to put it outdoors... at least during part of the day. In fotos 3 and 4 it looks like new growth is starting. Meyers in pots, when they are moved to new light conditions tend to drop a lot of leaves and replace them with leaves that are better adapted to the new light scenario. Considering that, when you are going to move the trees, it is best to do it gradually, as in sunlight to part shade to full shade to indoors; and the opposite when you move them out. Considering the age of the tree (small carbohydrate storage in trunk and branches) and the spider mite problem, I would say your young Meyer is not looking too bad. Yes, I would give it a little fertilizer now, try not to over water, and try to get it outside as soon as you can.

Welcome Emily and Hello John!

Emily, first and utmost, where do you live? When can you put your tree outdoors?

That tree is small enough to wipe every leaf off with warm milk and water often.

If it can't be oudoors for a while, I would watch your watering closly as John says. I must say it looks like it is in a great mix. Is that the 5.1.1 mix many here use? Mostly bark? Very porous?

That was a great catch on your part, finding the mites. Most would not be aware of this factor so my hats off to you for controlling it.

I would make sure it gets lots of sunlight at this point. even if it should drop all the leaves, at least the roots will stay strong and still push new growth accustomed to new light levels.
I have many times actually plucked every leaf off just to have the tree come back bushier than ever. They are more resilient than one might think.
I would of held back on fertilizing after an attack as so, because you don't want to encourage new growth in your warm , dry conditions unless you can figure a way to discourage mites from coming back to eat the fresh foiliage about to grow with 'constant' air movement aimed to blow towards under the leaves. Never shut your fan off and see if you can use a small table one with low speed.

If I have had a mite infestation,I would actually snip of all the new growth until I can almost put them outside to be on the safe side from stragglers then treat and treat all summer so I don't bring them in the following fall.

I always make sure the environment for mines are just right to reduce mites infestation possibilities.

For instance.

>If they are indoors, in my house, in a sunny window, I like to keep the room very cool with fans and moisture in which mites or any pests detest.
>For those in the greenhouse, I fertilize regularly for new 'strong' growth along with moist air, and air that is constanly being moved my fans.
I am not worried about spindly growth in this case or tender desirable leaves because they are getting all day sun and grow tougher.
In there, I deliberately let temps drop to the 50's at night though again which mites despise.
>At work, where conditions are very dry, I constantly wipe the leaves off those with warm milk and water, and shower them once in a while to keep the leaves clean.

Keeping your tree in a well draining mix, in a full sunny south facing window, leaves clean, fertilizing very lightly to discouarge fresh tender foliage until you are ceratin you have no mites, will help your tree make a full recovery in time for outdoors.

Please, don't fret if those leaves fall off, since many citrus shed leaves anyway for various reasons. As long as you are not loosing branches due to root issues caused by over or under watering or a poor soil mixture, it will come back strong once it sees the great outdoors if not sooner:-)

Mike