Answer: Unfortunately you are gardening in zone 6B, the warmer part of zone 6. Lantana is only winter hardy to zone 9 or 10 depending on the cultivar. 9This means areas such as Florida.) If you were in zone 8B (the warmer part of zone 8) then you might be able to overwinter it by mulching heavily and providing wind protection during the winter. But asking it to survive three zones is sadly just not realistic. If you really want to experiment with a lantana, there is one particularly hardy lantana called Miss Huff (Lantana camara 'Miss Huff') that is supposed to handle the cold into zone 7. I am so sorry I can't be more encouraging.
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