growing rosemary in Michigan

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?
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snipped-for-privacy@post.harvard.edu wrote:

give it a try, but don't be shocked if it fails. suppose you have 30 people in the house while the temperature outside is near 0F. The furnace won't kick in very often and the rosemary will freeze to death. same if you heat with a wood stove. the coldframe alone will give you 1.5 extra zones but you probably need three. a double layer coldframe may just do the trick but if strong winds knock it down, even once? That is all it takes.
My Michigan rosemary is in a 12 inches pot that comes in in october and goes out in april. Rosemary will take frost, which is why it goes out so early, and is undemanding as a potted plant (needs watering half the time compared to a regular houseplant for example, and little fertilization). That plant grows strongly (it is a very thick 2 feet bush) and gives us plenty rosemary. We also have large outdoor perennial patches of mint, sage, lemon balm, thyme, and oregano, all of which grow easily here, and I dry pounds of leaves in july and september. thyme, sage and oregano last well into december, so don't get discouraged.
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snipped-for-privacy@post.harvard.edu wrote:

What you want to do is grow something in a climate that is definitely not suitable. You will find that all evergreen perennial herbs are either very difficult or outright impossible to keep alive through the winter unless you have a greenhouse with controlled climate. The conditions inside a house in winter, while suitable for people, is not suitable for rosemary -- too warm and too dry.
You might also find that the summer rain in Michigan (a rarity in much of California, where rain is much more likely in winter) keeps the soil too wet for rosemary, which thrives in a Mediterranean climate -- cool wet winters, hot dry summers.
Also, don't try to grow citrus in Michigan either. Instead, try growing plants that appreciate a cold winter and that don't thrive in the mild winters of coastal or southern California. That includes many spring bulbs, apples, pears, and lilacs. While I can't get tulips to repeat from one year to the next because of a lack of winter chill, they should readily naturalize in your new home.
--
David E. Ross
Climate: California Mediterranean
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David Ross wrote:
David E. Ross Climate: California Mediterranean Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean influence (USDA 10a, very close to Sunset Zone 19) Gardening pages at URL:http://www.rossde.com/garden /
It would be nice to have pictures to go with your words.
--

Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8b
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