Plumbago may be a bit tender in the northern reaches of its range, but since it dies back in the winter, it's what you could call self-mulching. Add a bit of additional mulch after it dies back and don't cut it back until early spring, before new growth pops up, and it should do just fine in zone 5. It makes good bedfellows with spring bulbs because it wakes up on the later side, and with taller perennials as well. I remember walking into a nursery when I was a kid and seeing several untouched flats of plumbago, growing and blooming up a storm. Why untouched? Simply because no one knew what it was. Get to know this ground cover and don't make the same mistake.Photo by Wouter Hagens via Wikimedia CommonsMore great design plants:Black Mondo Grass | Blue Chalk Sticks | Cape Rush | Feather Reed Grass | Hens-and-Chicks | New Zealand Wind Grass | Redtwig Dogwood | ToyonGreat design trees:Bald Cypress | Chinese Witch Hazel | Japanese Maple | Manzanita | Persian Ironwood | Smoke Tree | Tree AloeGreat design flowers:Catmint | Golden Creeping Jenny | Pacific Coast Iris | Red Kangaroo Paw | Sally Holmes Rose | Slipper Plant | Snake Flower