When I was young, my Aunts garden was used by her neighbour to grow competition dahlias. Thew were very cosseted and often the flower heads covered in a paper bag .Ive only just started to appreciate them again especialy when they are in a mix such as you have. Think I might try some too.
The dahlia gardener used to dig up the tubas every year, pot them up in spring, then use the early growths for cuttings. (Im not sure that he didnt throw the old tuba away one the cuttings were going)