I am not quite ready to un box my stored tubers yet, but what I do is place each tuber in a sandwich sized baggie. with some moist - not soaking wet - peat moss. It allows me to have 20-40 tubers in a standard tray. I keep the baggie mostly closed until I see sprouts, then open it so the sprout doesnt rot. I keep some in a south facing window, and others under fluorescent lights. The baggies take up a lot less room than pots do. The fast growers end up getting moved into pots, but space is at a premium in my growing area, so pots are on an "as needed" basis.

The problem is that they arenÂt vertical. Since they were sprouting in the bag they are all more or less growing sideways. There was a limit as to how much I could straighten the tuber cluster in each pot since I was trying to keep the original (last yearÂs) stem upright. Now that they "know" which way is "up" they will undoubtedly turn up, but that will be at the tip of a laying-down section. (Unless I make them little bonsai crutches from popsicle sticks?)

Most likely the climate will do any necessary pruning for you. If they are chopped down, and the weather seems good to the tubers, they will resprout anyways until they chose to go dormant. Last time I was able to dig, I saw sprouts coming to about two inches from the surface, where the tip was blackened by the freezing temps about the soil. I am in zone 5, with light snow on the ground. My bet is that there is not too much growth down below the last couple weeks. ;-)

see if any of these might help: https://duckduckgo.com/?t=ffnt&q=dividing+dahlia+tubers&iax=videos&ia=videos and why is it important to you that they have less sprouts??? the tuber is a storage unit for dormancy and once new growth starts.. one would hope it would put down roots to feed the new growth .. and eventually store energy for next dormancy ... one would think that it wouldnt be relying on said stored energy for very long .. as once the leaves emerge.. and start processing sunlight into energy.. the plant wont be using the stored energy .. the only reason i could see to limit sprouts.. would be if you were a hardcore grower who plans on entering flower shows and your goal is one single perfect flower .. and if you were doing that.. i would think you would have years of experience .. and would know the answer all that said.. you seem to have multiples .. so make notes.. and experiment on different plants .. and see what happens.. many of us.. didnt have the WWw to confuse us .. lol.. and we just did a lot of experimenting ... and that was part of the fun .. and frankly.. i remember my experiments more than anything i ever read ... good luck and have fun ken