Last summer was the first year I grew the Main Street Oxford Street cultivar, and it is stunning. I grow coleus as an annual , planting after last frost in late April in my zone 7b garden. They keep growing and growing, getting up to 3-feet tall, until they die with the first frost in Oct/Nov. This past autumn, a neighbor stopped by and asked if she could take cuttings of my coleus just before the predicted frost. She said she roots and grows the cuttings in a vase of water over winter, then plants them out in spring. I had never thought about that, so I also took cuttings and put them in a vase of water. In fact, they have rooted and are doing fine. I don't see any growth, but the colorful leaves are a great backdrop amongst the flower bouquets I bring home from the farmer's market during the winter.
In my garden, we get frequent enough rain in the summer that I do not have to water the coleus frequently. I water them once a week if we do not get rain that week.