wouldnt the issue be.. whether that pot will support whatever size dahlia you have ....

so.. presuming they need a bigger pot ... i would get the new pot.. fill with media ... tip them out of this one.. root mass intact.. place it in the new pot ...at the appropriate height.. backfill accordingly ....and be done with them

i dont know why you think this is a propagation issue.. i suppose you might get more responses in the perennial.. or dahlia forum.. if there is one ..

good luck

ken

Put them in at Least at 12" pot and make sure that where those sprouts are are covered by 6" of dirt. They will come up'. Put a tomato cage or stakes for support. I don't know how big of dahlias they are but the bigger the pot the better flowers you will get. I put one tuber each in a 12" pot, and the whole pot is full of tubers by the end of the season when I dig them up. I divide and give to friends to plant in the spring.
For future reference, the little neck where they sprout, the sprout is called the "eye." Instead of planting them with the neck and eye pointing to the sky, lie them down horizontally (rotated with the eye facing up).

Thank you for for your helpful information. The main 'bunch' of tubers have just started to sprout also. I should have started them off ages ago, but we've had a prolonged cold spring and I'm wondering whether they're going to make enough growth to actually flower.

As for the 'eyes', I can never make out where the dormant ones are. Unlike the smooth surface of a Potato, Dahlias are wrinkled and fissured.

We bought some packed tubers a couple of weeks ago which have started to shoot already, whereas my saved ones have been decidedly slower. Maybe because the varieties are different, or the conditions in which they were stored.