citrus tree care sw florida?

This is not the time to fertilize the trees. But go your local Home Depot or Lowes and purchase citrus tree fertilizer.The growth may be just a fungus on the bark.

If I grew up in Florida and someone moved me to North Dakota, I would drop all my leaves, too. Citrus needs full sun and moderate to hot temperatures year round. That's why they only grow in the sun belt. I'm surprised it hung on as long as it did. If you do try putting it outside, do it gradually. That is, put it in indirect light for a week or so, then move it to filtered light for a week or so to get it used to the direct sun. Even a cactus will get sunburned if it was grown indoors and you set it out in the direct sun without acclimating it to the sun. If a plant isn't allowed to build up a tolerance, unexpected exposure to the sun will kill the chlorophyll in the foliage and the plant will likely die.