Cool article! I'm in Oviedo. I have an in ground tree that I protect in winter. It is 3 years old, so not yet clear exactly how much protection it needs. But it did survive the unusual cold a couple seasons ago with a shelter. I met an older gentleman at the Orlando tropical fruit club who has grown lychee in ground for many years. He said that his trees are oak sized, and their own canopy provides them shelter during cold. For the coldest winters that would kill even mature trees if unprotected, he puts a propane heater under the tree and aims to protect 8 feet of trunk, because the tree will then recover and still reform as a nice specimen. He said the trees own canopy holds in the heat of the propane heater.