what to do with potted clematis in winter?

I live in zone 5/6 in central Pennsyvlania. Two years ago I got some Evison Patio Clematis in very bad condition in 10" pots. When winter came I set the pots against a southwest stone wall of the house thinking that the wall would heat up enough in the sun to keep them from being killed. None of them survived. Last summer I got more of the same type of plants and I put them on the porch when winter started. Then we had a severe cold spell, and I got worried so I brought them into a basement with no direct heat and very little light. The temperature in the basement fluctuates from 40 to 50 degrees in the winter depending on how cold it is outside and for how long. I've kept potted rosemary and lavenders over winter the same way and never had a problem with them trying to put on new growth too early in the spring. But the clematis had other ideas. Even though they were only inside for two weeks they sprouted. I didn't want to put them back outside and risk losing them because they were sprouting from both the old growth and below ground. I thought I should move them to a lighted location so that they wouldn't become too spindly, but my girlfriend said she didn't think they would grow too far if I left them in the dark and that they might get too spindly in the house since they're an outdoor plant. So I left them in the basement. Now some of the sprouts are a foot long, with 6 inches between nodes, and even have buds on the tips. I'm worried that by spring the plants will be ruined. Can I save them by putting them near a south window? They probably would only get a few hours of direct sun, filtered through two panes of glass and a screen, but I don't know what else to do.
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Jim Shaffer wrote:

Jim,
Why don't you plant them in the ground where they belong? I have yet to see a Clematis that does really well as an over-wintered potted plant. You are going to have some warm weather the next few days in your area. Get them in the ground and put some mulch or leaves over them and in a couple of months you should have blooms.
--
Bill R. (Ohio Valley, U.S.A)

Gardening for over 40 years
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