This made me curious, so I did some web searching, and everything I found stated that this is an annual plant. If that's so, then by definition it is intended to sprout from seed, flower, set seed, and die all within one season. That is probably why you have never been able to keep it over.

Actually, this is one of those plants that is a tender (and short lived) perennial, but is typically grown AS an annual. A quick search indicated that it can be overwintered inside, though you may be happier if you take cuttings and grow them over the winter.

It can be difficult to transition a sun loving flowering plant from outside to inside. The reasons are many, but all have to do with environmental conditions. Natural sunlight can be extremely limited inside, as is humidity, etc. Lack of roots indicate improper watering, more than likely. Finding the correct balance of water when all of the other inputs have gone right down the tube is VERY challenging!

And THAT'S the reason why most of us treat these plants as annuals! From what I read, you could expect these plants to live on the same root system for as much as four years.

If you have the opportunity to set up some artificial florescent lighting, that might help. Make sure that you aren't bringing in a batch of spider mites, too. Cut the plant back severely, give it as much light as possible, and limit the water.

Calibrachoa hybrids are completly hardy subshrubs in zone 7 and may need some protection in 6. But they cannot overwinter in pots outdoors.

I have successfully overwintered calibrachoa. I have a white variety that I put in a south-facing window. From my experience, it likes a lot of water and hates drying out. My plant doesn't go dormant. Aphids are a real problem, which I keep in check using Safers Soap. A purple variety that I was growing did die the first year I tried it inside. Perhaps some cultivars are more resilient than others. I hope this helps.

Malcolm

This is an old thread, but I wanted to add (for the benefit of any current and future readers) that I had 2 calibrachoas overwinter in pots out on my patio. I’m on the edge of Zone 7b and 8a. One of them has been in flower for a couple of weeks now.

On the edge of 7a/7b had a calibrachoa to overwinter in a wheelbarrow planter in my back yard. Our lowest temperature over the winter was around 12. This plant is now blooming.

I have overwintered them in pots outside in zone 7 NC. One on my front porch is about 5' off the ground and came through hard freezes and bloomed all summer nonstop after that. I gave it a moderate haircut in the spring before it bloomed. It's out there again looking pretty scraggly. Don't worry if they don't look good till it warms up.