| Since they are considered evergreen subshrubs, I'd be cautious about covering their crowns with any type of heavy mulch like compost - it will only encourage rotting. Covering with old fir tree boughs or a light fluff of straw may be appropriate but I would most likely consider just mulching upto the crown of the plant to protect against heaving or freeze/thaw cycles, not over the top of it. Otherwise, a good snow cover is one of the best insulators. |
Here is a link that might be useful: growing heaths and heathers in cold climates
