Since the sawdust has some carbohydrates in it, which furnish energy for microorganisms, it is helpful to add about one cupful of ammonium sulphate or three cupfuls of cottonseed meal for each bushel of sawdust. Otherwise, the stimulated microorganisms compete with the plant roots for nitrogen. Some plants that need mulching in summer should not have much mulch in the winter where there is danger of sudden cold snaps. Some of the azaleas and other tender plants fall in this class. With a sudden freezing cold, the only source of heat for the lower branches and the main stem is that coming up from the soil.
Little heat can come up through a mulch.
The mulch acts very much like the material in the wall of a refrigerator. So, for those kinds of plants, I remove the mulch around the stem in late autumn. Also I wrap the stems of the tender ones up to 2 or 3 feet with masking tape. This helps prevent freezing and cracking and if freezing does occur, the tape prevents the movement of moisture out of the plant so the crack may heal later. In fact, it is a good idea in planting a dogwood, or any young tree, to wrap the whole stem with masking tape and keep it on until its roots are well eslablished.