Answer: Lantana can be hard to keep indoors because it likes a lot of sunshine, it is really best if you have a greenhouse.
Often, it can defoliate due to being moved (shock) or due to overly dry indoor air, or due to pests, or due to overwatering (quite common when moved indoors because the lower light levels cause them to grow more slowly and need less water.)
If you want to try to keep it growing and blooming for the winter, you would need to bring it inside gradually when the weather begins to cool, bringing it in at night and setting it out on warm days, setting it indoors in the brightest location you have, and water lightly so as to avoid an overly wet soil that would encourage root rot. A cool room temperature, about 60 to 65 degrees seems to work well.
The other method to try is to let it go basically dormant and keep it in a cooler area with the soil just barely moist (not bone dry) where it can rest until spring -- a temperature in the 45 to 50 degree range is ok (eg a basement) and it may be dark or bright.
Either way you will want to cut it back at some point to stimulate vigorous new growth next season. Since your plant has already defoliated, I would suggest cutting it back now. This will also make it a bit easier to control any pests that may have hitchhiked inside with it.
These plants are often attacked by spidermites and/or whitefly and these pests both breed very fast under dry indoor winter conditions. They may also cause defoliation, so check it carefully for signs of infestation. You can treat both with insecticidal soap applied and reapplied according to the label instructions. Spidermites also decrease under more humid conditions so setting it on a pebble and water tray can also be helpful.
Remember also to cut back on fertilizing for winter, if it is dormant it needs none at all, if growing actively it might need only half or a quarter the regular amount.
Next spring when the days lengthen you can begin to water and feed it a bit more in proportion and then gradually reacclimate it to the outdoors once the weather settles.
Be patient waiting for it to leaf out again -- Good luck with your lantana!
Q&A Library Searching Tips