The previous owner of my property planted an Hibiscus shrub against the south-facing wall of an unheated garage, and the shrub has now got to be about 15 years old and it reaches as high as the garage roof. It's currently covered in blooms. I don't know what the name of the variety is, but it must be very cheap and common, as the folks who lived here before me were pretty frugal. Here's a pic of the flowers, maybe someone can ID it: