In the old house, I would put a few plants into our crawlspace every fall and let them go dormant. I have been able to keep geraniums and mandevillas alive for years that way. I'd put them away for the winter. No water, no sun. They'd look dead, but come spring, I'd put them outside and they'd come back to life. It would take a couple of months before they looked decent, but it worked.
As we were moving, I brought some of my plants inside the house. Since we were still working in the main rooms, I stuck the plants in the attic space. We have a large, well insulated attic just off the loft. There are windows on each end. By the time I moved the plants there, they were already looking pretty lousy - they'd put on their show for the year and were done.
The plants did well in the attic. They continued to grow even though I kept forgetting to water them. About a month ago, I moved a few of them to the south windows in the loft. They are really bouncing back.
The mandevilla has new growth. I'm probably going to prune it back soon. I read in an article about overwintering mandevilla's, that this should be done. As you can see from the photos above, it's pretty leggy and needs pruning. The tips section also says you can root this plant from cuttings. I've done that from a number of plants, but had no idea mandevillas would root. Yeah!
The geraniums LOVE the sunny windows. I've never been able to keep geraniums blooming like this.
And here's the biggest surprise - I have cherry tomatoes. This plant looked pitiful when I brought it in. I thought it would be ditched soon, but I just wanted to see how it would react - sort of an experiment. My goodness. I've already had 8 cherry tomatoes from this plant and it continues to flower. I wish I'd brought it in when it still looked pretty nice.
One of these days - maybe next year - I'd like to grow lettuce indoors. I read about it ages ago and the article intrigued me. This person kept 3 or 4 lettuce plants going all winter and tore a few leaves off every time she wanted a salad. We eat a lot of salads around here so that would be great!