We just moved to Mid-Michigan from Northern California. Just about the only thing we miss about our old house was the ability to grow herbs year-round, particularly rosemary. We would like to find a way to keep rosemary bushes alive through the winters here (zone 5b). I've read that it is sometimes possible with the hardiest varieties in sheltered areas.
We just replaced the original furnace in our 50 year old house and as part of the installation, a new exhaust pipe was routed to our foundation in the backyard. The result is a lot of warm, steamy air comes out of the house near the ground in a particularly sunny spot. I'm wondering how I could take advantage of this situation for the rosemary. One idea I had was to make some sort of cold frame near the vent to capture the heat without shocking the plants too much. Any suggestions?