I've found that I can "Zone Push" w/ plants that are in containers that are either on my blacktop driveway, or crushed gravel surfaces around my house. I use the plastic "self watering" containers on the blacktop, otherwise they toast during the summer.) I find that the coleus and begonias on my South and West facing wooden decks get nipped by low temps much, much sooner than the same cultivars on my North facing crushed gravel entryway!
I use large and small stones everywhere in my gardens. The stones capture heat, so anything growing near them also survives an extra week or two in the fall. In the Spring, the "stone effect" doesn't seem to work as well for some reason.
Crushed gravel, huh? We got our first frost last night and from the window I can that my planters on the blacktop driveway are fine -- but I refuse to go outside & check on damage until the temp hits at least 45!