I would also ask this in the "Growing Under Lights" forum, but my two cents:

Humidity is important -- the best thing you can do is use a humidifier, but anything you can do will help. They should thrive under fluorescent lights, but sunlight helps as well. You aren't going to burn a coleus with a fluorescent lamp. You only need to keep the lights maybe 6"-12" away from the plants. I would go with a 16 hour on/8 hour off light cycle.

I agree with this, as much light as you can. They grow in the sun, and need a lot of light when you bring them in. I'm going to do it, too, this year.

Well, here's an update. I followed the advice from the "Growing Under Lights" forum. Some one their recommended lights within 2" of the top of the plants and to run the lights for 16 hours each day. So, I set the timer, zipped up the plastic tent and went away. I did water once, a few weeks ago, and again today. Well, I now have a jungle of coleus plants. Several had grown up past the light, but those were mostly flower stalks that were probably started when i brought them inside. Some plants were already rooted, and some I rooted fresh at the time of my first post. Everything is thriving. I do have some gnats buzzing around, and I purchased a few of those sticky fly tape strips to hang inside the plastic covering to minimize their spread around the house. If my plants continue to grow this well, I could easily continue to take cuttings from the cuttings I already have, and end up with a hundred or more plants. And, under the artificial lights, the colors in the leaves are beautiful and rich. So, thanks for your help and advise. I'll try to keep in touch as the winter progresses. I'll also need to check my electricity bill. Adding another layer of lights would double the power needed to run my little hobby. I did take some cuttings from a coleus that a friend was tossing at the end of the season, and also some cuttings from my outdoor Persian Shield. As mentioned above, some people have success just keeping cuttings in plain water through the winter and planting them out in the spring. I may just try that. Though, I wonder if a longer winter has a greater chance of complications if plants are simply in water. My winters are pretty long, with first frost in early October and final frost or plant out date is June 1st. As the climate warms everywhere, those dates are less accurate, but we still have pretty cool night and soil temperatures for tropical plants. Best of luck to all.

Martha

Martha, that's exciting, thanks for sharing your great results! Those Coleus flowers are a heart-warming sight when it's cold out but boy, don't they make a mess? I wonder if they'll stop with the lights on that many hours. Does it look like the flowers are winding down or are there still buds forming?

I used to do the cuttings in water when I lived in OH (along the border between z5/6). The extended time can be a factor if trees leaf-out and make shade on your windows in the spring before it's safe to put the cuttings back outside. That's a good point.

Purplinpop,
My coleus are still growing beautifully. I don't have many actual flowers. I usually nip off any flower buds as soon as I see them so the plants don't waste energy on flower production. The foliage is beautiful enough for me. I'm wondering whether I should cut down on the hours of light. I don't need rapid growth, just enough to keep the plants alive for transplant outside in the spring. Does anyone know whether shorter light days would result in spindly plants or pale leaves or mildew or anything else unpleasant? I'd rather know what to watch out for. Actually, everything is going so well, I probably won't change anything. Thanks for following along!

Martha

I'm cheering for your plants! Smiles!!

I just finished a major trim job on my coleus monsters. I think the cuttings I rooted have done even better than the established plantsI already had. So, I'm tempted to toss the old plants and start new with all fresh cuttings. But, that would require a major effort and tons of potting mix. I'm trying to get ready for the wintersowing season. Oh, well. Too much gardening is a nice problem to have. ; )