Well, I can tell you what happened to my key lime tree (potted). I accidentally left it upstairs in our unheated attic for part of the winter. We had temps in the teens and it got pretty cold up there. All but one little branch had died, and the branch that was still green had dropped all its leaves. I was so bummed because I had had it for 2 years and hadn't gotten a single lime from it yet. I took it inside and warmed it up, hoping for the best. It survived and during the summer grew really well! Since it had died back so much it didn't produce any flowers, but it grew a bunch of new leaves and branches and still looks pretty good! That was last winter.

barrooze, well the next time you repot it, you can up right your citrus...it looks healthy.I would feed it at least 1/2 Cup every 3 months.Get it out of the wind for one thing.And when your blooms turn into baby limes you may pinch a few here & there if you'd like.Lime trees can take temps down to 28 degrees, although this is pushing the envelope so to speak,I never let mine get to below 34 degrees.I think it makes for a healthier plant if they experience alittle cooler weather thru the year.But the wind will harm them. Suzanne

Barrooze..35F degrees is pushing it..How long, hours/days do temps dip under 40-45F? Yep, wind, especially cold, strong winds causes damage. I don't know how to compute wind chill, but if the temp is 35, and winds are 40mph, let's just say I wouldn't want to be standing there..LOL.

One way to tell if a plant needs repotting is roots grow out of drainage holes. And/or, if soil dries out daily.

Any stems growing under a graft-line should be removed; once you spot it/them, cut ASAP..if you wait too long, it will take over, and eventually kill your citrus. Older, thicker stems leave scars on trunk which is another reason to remove promptly.

There's no reason to prune..

Foliage yellows for different reasons..over and under-watering, mites, nutrient defiency.

It's best to rotate plants 1/4 turn each week..I'm assuming your plants have been indoors during winter months, before a window..Rotating prevents plants from reaching for the sun, leaning.

Fertilize times/dosage according to directions instructed on Vigoro package. Never exceed dosage..it's better to under than over-fertilize..

It's normal for flowers/fruit to drop...but, be sure soil isn't continuously wet/muddy..Citrus are sun-lovers, so winterize your tree in a sunny south or west window. I too believe citrus kept cooler in winter do best. Avoid areas where artificial heat aims at plant..same w/a/c. Provide humidity, keep foliage clean, and use well-draining soil. Toni

It almost appears as if your lime tree is a cutting rather that a budded tree. I see multiple branches growing out of the soil but all have the mexican lime leaves. So as far as your 3rd question I don't think you have to worry about suckers growing from the base. Your tree looks very healthy with all the new shoots starting to grow. I wouldn't worry about the older leaves turning yellow and falling as long as you have new growth. My mexican lime almost defoliates completely in the winters here (it lives outside in zone 9) after cold weather and winds come along. It is no big deal.