How can I preserve and propagate a color sport in my dahlias?

Question

I have several Hulin's Carnival dahlias in my garden, whose flowers are normally white with flecks or large patches of wine:

This year, one of them has put out a stalk that has pink flowers instead of white, keeping the wine flecks:

I would like to preserve this color variation and propagate it if possible. Since it's now fall, I don't think stem cuttings would work (but would be happy to hear differently). These particular dahlias are under an overhang from my porch, so I've been able to leave them in the ground over the winter. If I do that this winter, is a pink flowering stem likely to grow from the same place on the tuber next year? Would digging up the tuber and dividing off the pink-flowering part give me a better chance for success?

Answer 1

Hmm, well I'm in two minds on this one. You've said its only one stem that's produced this sport, so I think I'd be inclined to leave the plant alone this year, then wait and see what it produces next year, which should give more time for the tuber which has produced these to get bigger and have more eyes (from which growth comes). You can take cuttings from dahlias, and it might be worth doing this when growth has begun and the plant is about 8 inches high. They are best taken with a little bit of tuber attached at the base, leaves removed apart from the very top two, and potted in a free draining mix, in an enclosed environment to keep the humidity up. 4 bits of stick and a plastic bag over the top, with a rubber band to keep it in place, will do this job. The obvious problem with that is, you won't know which stems are producing these sports. The alternative is to leave it alone this year, wait and see how many of the sports are produced next year, mark the spot and then dig up the tubers at the end of the season and remove the one you know is producing these, which should be much bigger next year.