Gardeners love to push the zones, growing exotics or plants that are marginally hardy in their particular area. A plant that is tender in one zone may be perennial in warmer zones, so gauge your conditions and the plant’s indicated hardiness before deciding what winter treatment to give it.
Protecting plants in the ground
Plants left in the garden can by done in by cold, wet or wind or a combination thereof. The leaves and stems above ground are likely to be killed off with cold air temperatures so focus on protecting the roots and the vulnerable crown (the juncture of stem and roots) with a layer of insulation.
A blanket of snow is one of the best insulators—one study showed that each centimetre of snow cover increases soil temperature by roughly half a degree Celsius. But snow cover is unreliable. Mound dry leaves, peat moss or straw at least 15 to 20 centimetres high over the crown and root zone, holding it in place with an overturned bushel basket, netting, fabric or evergreen branches (the last will capture any snow for additional warmth). Maintaining more consistent moisture and temperature this way also reduces damage from freeze/thaw cycles.
Cover the crowns of plants that dislike winter wet with leaves or straw under a glass or plastic cloche. Lay conifer branches or burlap over cloches to prevent overheating from the sun. Wind can be very drying so planting in a sheltered spot to start with will be beneficial.
Note: Remove protective covers gradually in spring when temperatures are above freezing.
Top image from istockphoto/BrettCharlton