Kristen, it's "turd" not terd. I'm pretty sure. LOL and an apt description!

To answer your not-dumb-at-all question: what usually falls off those field grown clumps are non viable tubers. They need to have a piece of the stem collar from the previous year's growth with a viable eye (should be raised bump, possibly pink or light green in color by now, but some varieties are slow to show eyes.) I would wager your clumps are fairly tightly bound together and perhaps a growth shoot or two are emerging close to the visible old stem? If that were the case, you could hack off (carefully trim) all but the one tuber supporting that "eye" or growth shoot. If you have two shoots showing up a ways apart in the dreadlocks, you could ostensibly chop that clump in half and get two separate dahlia plants as long as each shoot had at least one tuber supporting its growth. Let any cuts you make dry for a few hours, dust with sulphur or spray with Lysol spray for fungus control and plop them in the ground.
If I get a field clump like that I just take my pruners and lop off any broken necked floppy, loose tubers right away- they do not serve the plant any way at all.

Good news on the 5 gallon containers. That should be way ample to accommodate any tuber or dahlia clump. People on the dahlia forum even plunk them right into the ground, planter and all. Easier to dig up and less destruction to tuber clumps come Fall excavation time. Also less prone to tipping over than if the container was on top of Mother Earth. Perhaps in your greenhouse, wind and rain wouldn't be an issue, but outdoors they wreak havoc on a tall plant laden with heavy blooms.
The only trouble with growing in containers is staking a tall plant. Some of my 'four footers' have exceeded 6-7 feet. If you have shorter varieties, that won't be such an issue but my experience is that almost all dahlias over 2 feet benefit from staking and supporting somehow.

Hope that helps.

some other information can be found int he dahlia forum. I've found that forum very helpful in growing my dahlias. :o)

Don't mean to hijack your thread Kristen. But, I was wondering--Do any of you grow dahlias in a hoophouse?
If so do you have suggestions for varieties that would do well for this.

Poochella, I meant to thank you and say that's EXTREMELY helpful for me-- I had no idea! I have 25 dahlias potted up and 20 of them are in 5-gallon pots and five are in smaller pots (i'm not sure- maybe 3 gallon? The one-step-down size from the five gallon at the nurseries...)

And, Irish Eyes, it's fine with me, because that's where I intend to put my pots of dahlias-- in the hoophouse! We have pretty cool nights around here and I figure they'll bloom taller and grow better in there. But we'll see!

Kristen

We are growing some of our dahlias from tubers in pots in the hoophouse. The intention was to sell these potted dahlias at the market. Our pots are 14" across by 11" in height. They hold 7 gallons of growing medium. The plants are HUGE. Needless to say, they are very happy! We didn't put clumps in the pots. Only one dahlia tuber. I am wondering if your 5 gallon pots are going to be too small. And, 3 gallon is going to be way too small in the hoophouse. These things get really topheavy when grown in the hoophouse. It isn't at all like growing outside. You might want to consider this if you are going to be growing the dahlias in your hoophouse. In the hoophouse sun and water = tropical conditions.

In another hoophouse we have the Karma dahlias growing right in the ground on one foot centers. The beds are 4' wide and 92' long. The dahlias will grow 6' tall in the hoophouse. Currently we are weeding in that hoophouse. The weeds are never ending.............