I puzzled over and over about why it happened. Finally, one winter I decided to take new cuttings from one of my fall-propagated plants that I suspected was beginning its downhill slide to the compost pile. I made every cutting I could from the declining plant. These new cuttings rooted on the heat mat just as well as the ones I took in the fall, AND the older plant began putting on new growth without problems. By spring I had lots of new plants and the original was in great shape to go back out for the summer. I don't pretend to understand the physiology of what is going on. I just know that I have found it works for me. Now I plan on taking more cuttings from these problem plants early each new year. If you don't want or need more cuttings from a plant, just prune it back by about a third of its top growth and continue to maintain it in the same way you had been doing until time for it to go back outside. Here are some observations on the response of various plants to this technique:
The plants that I can only keep this way are coleus (Solenostemon), chicken gizzard (Iresine), Persian shield (Strobilanthes), and Joseph's coat (Alternanthera). Since one of my problems is that my basement is too cool (down to the low 50s at night in winter), you may not need to do this as I do, but it is a good way to increase your plants should you want to.
