I used to grow bananas when I lived in Oklahoma City. I would simply take the roots and plant them out in spring, then dig them up and store them in the crawl space under the house for winter. The "trees' would get about 8 feet tall during the summer. Of course these were the large type, not the dwarf ornamental type. It was always so nice just to have that tropical feel in the yard. But we didn't ever get bananas. I also have had orange trees, lime trees, etc. There is nothing nicer than the smell of orange blossums. I just kept a tree in a large pot and brought it inside in winter. I did have a lot of southern windows in my old house and this house doesn't have any good ones.
Well when talking about an underground greenhouse I was talking about a large one. At least 20 feet wide and maybe 40-50 feet long. I do know where there is one, but I don't know the people or I would ask to go look at it.
I was gone all afternoon. I sold some birds this morning as well so it's been a busy day. I got to watch my granddaughter for a little while today. We're just far enough apart that hasn't ever happened before. I really enjoyed it. She is 5 years old and talks like she is 25.