Cellular respiration in plants is slightly different than in other eukaryotes because the electron transport chain contains an additional enzyme called Alternative Oxidase (AOX). AOX takes some electrons out of the pathway prematurely - basically the energy is used to generate heat instead of ATP.
The exact purpose of AOX in plants is still unclear. Plants will make more AOX in response to cold, wounding, and oxidative stress. We know of at least one plant (skunk cabbage) that exploits this pathway to generate enough heat to melt snow thats why you see them poking there head out when there is still snow on the ground
Plants will be respiring continuously, which is an exothermic process. Therefore the plants will be producing a small amount of heat. The protection from frost may be more a result of the vastly smaller convection current of the coat compared to the atmosphere rather than by reducing any conduction away of heat produced by the plant, however.
Keeping the plant out of the wind by 'dressing it' will reduce the rate of transpiration when the stomata are open. I would very tentatively suggest that, as water has a very high specific heat capacity, having a greater volume of water within the plant would help to retain any heat that was produced by respiration. However this is entirely speculation on my part.
But then again technologies be getting better every day so who knows what they can do now and aint tellin 
