Jeanna and I planted….well we tucked actually, the Spanish Moss into branches of the Live Oaks in the National Grove of State Trees mid-summer 2008. They lived through last winter which included a few nights of single digit temperatures (Fahrenheit).
Generally, when it’s given a hardiness zone rating, Tilia u. is rated a USDA Zone 8 or 9. Widespread throughout the south, there are regular references in the literature, to its occurrence in Maryland though its more likely to be encountered in extreme SE Virginia. After years of observation, my, untried, conclusion/guess is that while temperature is definitely a limiting factor, a lack of winter moisture is what really draws the line.
During winter visits to the Florida garden, I noticed that a combination of unfrozen water, humidity, and nighttime temps that regularly drop below the dew point without freezing, combine to produce heavy heavy dews. It isn’t unusual for the windows to be opaque until the sun dries things out. Regularly Tree frog tracks in odd arcs, ornament the sliding doors. It largely evaporate later in the day, but every morning all the plants including the Spanish Moss are dripping wet. These conditions coincide with the dry season, dry in the sense that it doesn’t rain. Still, moisture is moisture.