I'm going to do this same thing. I bought my (5) lavender plants at a sale in the spring and grew them in pots on the front porch over the summer. This fall I'm going to sink them into the raised bed to overwinter, pots and all, and find them a permanent spot next spring in the cottage garden. I've had luck wintering over other things this way.

Skibby and mamabear, lavender can be tough in this climate mainly (I think) because it hates wet and wants to be very dry. I'm certainly no expert on lavender, but you might have better luck with them if the pots are both raised a little higher than the surrounding bed and the bottoms are cut out so water can drain very freely as the snows fall and melt and refreeze.

I started some from seed this year and they are in a high raised rock bed. Hoping they do well. I remember that the Canterbury Shaker Village in NH grew lavender successfully for years by layering the top of their soil with light-covered gravel. The gravel helped in drainage and the light color reflected the sun so they got more of that heat they loved. I've got gravel, still in a bag....that I meant to put on them all summer. Trying to decide if I'll put it down before winter.

Do you think they would be happy in the garage where it's less cold? They won't get much light, but it'll be warmer and I can control how much water they get.

I wouldn't put them in the garage since the light is so low and they retain leaves. Also, it may start trying to grow in really early spring (like February) and exhaust its stored energy.

The only time I have successfully overwintered lavender in a pot, it was a large pot and I laid it on its side on the north side of the house and made sure it stayed buried in the snow. Winter wet is the enemy of lavender, and freeze-thaw cycles aren't good either. The combination of having the pot on its side to keep rain and snow from the soil, along with staying right at freezing due to being buried in snow kept it as happy as possible in our cold, wet climate. No guarantees, however.

I don't know where skibby is, but the only in-ground lavenders that have survived my winters in the ground (well enough to look good the following year) are 'Phenomenal' which is hardier than most. They are planted in really well-drained soil, either at the top of a rock wall or slope, or in very sandy soil.

I've never successfully overwintered lavender in a pot, but have a dozen plants in the ground that overwinter great. It is sandy, dry soil and they flourish. I can't keep them alive in a pot no matter what I try, so I've stopped bothering.

Regarding overwintering in a garage. I have successfully overwintered prostrate rosemary and lemon verbena. Lemon verbena goes dormant and loses leaves. Both plants should be watered sparingly. They got only a tiny bit of light from a north window. But I think the big thing is our attached garage rarely gets below 50. We didn't plan it but because of a nearby triple flue chimney and heat from a basement wood furnace plus garage concrete floors, we seem to have a thermal mass that keeps our garage much warmer than most here in the Concord NH area. It is also fairly well protected from westerly winds by the barn. I don't mean to go off topic but I just want to point out that anyone considering overwintering in a garage needs to think about how cold their garage gets. In the high tunnel an upright rosemary survived one winter then died the second. Next to it purple sage has thrived. I put large tomato cage over the plants and covered with several layers of agribon fabric. I don't quite understand it since the high tunnel is just covered in greenhouse plastic but the ground inside doesn't freeze. On sunny days it can get very warm in winter but will get just as cold as outside at night.

The teepee out of pine branches for wind protection makes sense. I wonder if the same could be accomplished with tomato cages and several layers of agribon. I think people also need to be aware of what their soil area is like in the wet spring. I have a section of my perennial bed that becomes waterlogged. We have a very high water table. I'm not growing lavender right now but suspect the walkway bed that is edged with one board on the lawn side would be a better location. That bed gets much better drainage because the lawn slopes away.

Come to think of it, a gardening friend a couple of miles from us has a beautiful lavender bed. Their yard is at a low elevation (river several hundred yards away across the road) and they tend to get an early frost. I'll have to ask her if she gives the bed any protection.