Cold protection is a fascinating topic, but does anyone know of any scientific studies based on field trials with a large population sample for any tropical plant? aroids, crotons, palms, cycads, pick your favorite....
...and what do we mean by cold protection? Are we trying to prevent the plant from defoliating, turning to mush, or survival with some damage.
..and what kind of cold? is there a threat of frost? Some plants will tolerate freezing or below but will not tolerate frost (some cycads come to mind here). How windy will it be?
What is the relative humdity (other than too low)? Although plants do not feel 'wind chill' the way we do, drying and desicating winds can cause a lot of damage in addition to the cold temperatures.
..and let's not forget we are dealing with a genetically unstable plant here. A few of my crotons (Queen Victoria and Interuptum) defoliate quite easily while crotons right next to them survive untouched. Sometimes one Interuptum will defoliate and the other will not. So here's what I do based on the severity of the cold snap.
For any cold snap, water well ahead of time. Wet or damp soil retains more heat than dry soil.(The specific heat of mud is higher than that of dry dirt). I figure the plant also has some moisture available to it to prevent gross transpiration losses in leaves due to low relative humidty and drying winds. Never water if the water will freeze. Check those irrigation timers.
For temps forecast to stay at or above 32F, I may move a few primo plants into the house or garage. Everything else is on its own.
For temps below 32F and low to no wind but a threat of frost, I'll cover the frost sensitive plants if they are not under a canopy.
For temps below 32F and high winds, no threat of frost so no need to cover to prevent frost burn. Covering almost anything is futile since the cold air works its way in all too quickly and covers blow off unless securely anchored.
For something like the 12/1989 freeze, get the chain saw ready.
If a croton gets badly toasted, I wait at least two weeks or more before doing any pruning of damaged branches, and usually longer since we may get another shot of cold air depending on how early or late in the winter. Almost all crotons will recover if lowest one foot and the roots are not damaged. (Think of roses up north). My not-too- bright neighbors chopped some crotons down to ground level to replace some windows; six months later, they were at least two feet tall and healthy looking.
Fortunately, the low this a.m. here in south St. Pete was 38F.