I don't have a warm greenhouse, but have you tried it in the house? I could try that for you- i have windows in all directions- surely one exposure might work?

Back when I grew it I tried it every way possible and never got it to last until Spring. I think it needs supplemental light, that our winter days are too short for it. Keeping it warm and moist is one thing but I think you'll need a light source on a timer to give it 12 hours of daylight each day at least.

I overwintered mine in the house last year. I have a large window that faces east and can get some south sun during the winter. I overwintered all of my cuttings (hibiscus, coleous, brugs, elephant ear babies, etc) with no supplemental light. I had to turned them every now and then to keep them from leaning to one side, but aside from that, they made it through just fine.
I suggest that you don't over water them. In my experience over watering in winter is the major reason for any plant failing to survive. There were times when I only water them until the soil felt almost dry and the pot was light and I picked it up.
I'm hoping to overwinter mine this year again. I just dug one out of the bed to make room for other plants and the remaining one is about 5 feet wide and 7 feet long and I have trimmed it twice during the year :0)

Monica

Ralph, my greenhouse will be up and running in about 3 weeks and I plan on keeping it warm enough to get my coleus through, so it will probably be warmer than yours. I've never tried to overwinter 'Haight Ashbury' but I'd be glad to give it a shot.