I overwinter hardy perennials that are in containers by placing them against a wall and then stacking a bale of straw against them. I often use gallon containers or quart pots, and if they're herbaceous and not shrubby, you can stack the quarts once the foliage is gone. I will frequently grow them on in containers if they need some size to survive in a bed, or if I want to see the real habit of the plant or color of bloom before I plunk it in a bed. Or, if it's a plant that needs "crowd control" like mint, bamboo, gooseneck loosestrife, etc.
If there is space between the pots, I fill with shredded dry leaves. Wet leaves will yield slimy black goop, dry leaves will be almost composted by spring. The straw will be ready for mulching the vegetable garden.
