By Ponty
Norfolk,
United Kingdom 
Firstly, hello to all my old friends. I have been away for some time. I hope you are all well and that your gardens are thriving.
When retrieving my Dahlias after over-wintering last Spring, I accidentally knocked off one of two, three inch shoots from one of my favourite varieties. Having had no experience of propagating Dahlias I planted it in a small peat pot and said a wee prayer. Some weeks later I was delighted to find that two small shoots had developed. After the shoots had grown a little I potted it on and eventually placed it in the greenhouse in a 7 inch plastic pot where it now stands some three feet tall.
I am now unsure as to how it should be over-wintered. Is it mature enough to have developed a tuber or should it be left in the pot? I do not wish to disturb it unless there is a viable tuber.
4 Oct, 2013
Answers
Thank you Bamboo. I had a gut feeling that you would pop up with the right advice. I am sorry I took so long to respond but we had been away for the week-end.
8 Oct, 2013
Previous question
Takes 1-2 years to form tubers - at the size it is, it's likely it has formed a tuber, but what you could do is leave it in its pot and reduce, then stop watering as the growth dies back. Provided its kept in your greenhouse and not watered, and doesn't get frozen, it should start itself into growth next spring, and you'll be sure next year that it does have a viable tubers.
4 Oct, 2013