By the way, here's a photo of the tubers in question.

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(The leaves are from the Hackberry tree above the table.)

Divide. You answered your own question -- the plants will be less robust & not bloom as well as when they're striving to put out flowers to propagate themselves.
You get a stronger, healthier plant out of a single tuber-- & have leftovers to trade or sell!
Some people think you have to have a big clump- or a BIG tuber for a good sized plant but you don't. A smaller tuber will grow into a big plant because the tubers put out feeder roots to support themselves when planted.

When you divide the tubers, how exactly do you do that and what do you divide? Do you cut with a knife all the 'potato looking' tubers individually? I am very new to gardening and I have already dug up mine. I'm not sure how to divide or when.

Heather,

Here's a pretty good video that covers it all.

http://www.taunton.com/finegardening/how-to/videos/digging-dividing-storing-dahlias.aspx

And this tutorial from Dahlias.net.

http://www.dahlias.net/dahwebpg/TuberStor/TuberStor1.htm

FYI, Dahlias were first brought from Mexico to Europe in the hopes they might replace or augment the potato crop. They are an acquired taste, I'm told, so that idea never flew.

Cheers,
Russ

Here's more instructions-- In the "From Seed to Dahlia in Picts." album. If you click on the pictures of Walt cutting up tubers, the picture will get bigger & the instructions will come up- or view as a slideshow & the instructions are there, too.
He only has about 200 plants left to dig, divide & store out of around 7,000!

Here is a link that might be useful: Cutting tubers

I also have a question. Should you divide after you dig or before you plant next year. My mother said to wait until next spring but then again she told me to put them in peat moss.

Don't feel to bad Monica my father told me they would not land on the moon in my life time.

Thanks for the great advice! It helps out a lot. Now I actually can do this without thinking I'm going to kill them.

Wow, plantlady, that is an amazing instructional presentation you have. W O W !

Thanks for sharing. I showed it to my wife, and she doesn't feel so bad now about when I take over my garage with tubers. LOL

Russ, that was a good video. Thanks for sharing.

Hello Plantlady,
That is a super video you have made. I really learned a lot. I have never dugged the tubers of the dahlia, and it now about 3 years. I have all my dahlias in a pot. I guess, it is about time to dig them up and divide.
I was wondering if you have anything regarding hybridizing, like where is the pistil and stamen of the dahlia flower, or how do go about putting the pollen to the mother flower.
Mary Ann

Monica33flowers- Walt divides in fall-- the clumps are easier to cut-- in spring they can be quite hard -- in fall they're still green. If you cut the plants down & then wait 4-7 days before digging they'll pop eyes so you can see where to cut. Also - they take up less room after they're divided. Or if the plants have frosted down, wait a few days, providing you're not going to get really cold weather & the plants will try to re-grow then you'll be able to see the eyes.
jroot- I'm going to take a picture of Walt's discard pile & then one of the cold room in the basement - you can show them to your wife & she'll never be able to bother you about taking over the garage again. >:)
Mary Ann- If the clumps have been a pot for 3 years I hope you can get them out without damaging the pot! If the clump is really big just whack it in half with a machete or other large tool. Then cut each of the halves in half again so you have a managable clump. Then you can start cutting the tubers off- be sure to leave some of where the tuber meets the cut off stem or your tubers won't eye up & grow.

I pulled up my dahlias and this is what some of them look like. I'm not sure what happened to them. I had them in my garage to dry out a little and when I went back to them about a week later, this is what I found. It's like something got ahold of them and sliced 'em open exposing the insides of some. I really hope they aren't ruined because they were beautiful flowers! What would you suggest???

Thank you,
Heather

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Oooh, pretty bloom Heather. Even though blurred, it appears from your photos that you have had an invasion of underground munchers nibbling on your tubers. We have moles here, and where moles drill, mice will follow as Plantlady instructed back in time. Tubers that have been nibbled here look much like yours.
Here's an obvious example of chew marks on tubers. If it's not too bad, I'll try to save the tuber, but if they're really gnawed, toss them. A cat makes a fine garden companion.
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You are very right!! Last night I went into the garage and startled some of my nasty problem. I saw a couple field mice running out as I turned on the light. I'm going to set some traps to try to catch them but we live near the Ohio River and I'm sure there are lots more of them. Should I do anything to the tubers? Mine looks a lot like what you have in your picture. How do I keep the mice out? It's going to be very hard figuring I don't know how they are getting in. What should I do with the tubers to keep them safe? Could I store them in plastic food containers you think or would they not survive in them? I know mice can eat through almost anything and I'm scared for my beautiful flowers because the boxes I have them in aren't doing a good job keeping them out...

Thank you!
Heather

Traps or some sort of rodent control device would be good. The colder it gets, the more tempting your garage will become. I like the Rat Zapper as it seems more humane and less dangerous for my valuable fingers than those blasted traps!

What do you with your dahlias: I'd decide what is too chewed to save and cut off or discard those. If anything is lightly chewed, and you really want to try and save it, you could
1) Spray the chewed zone with Lysol. I don't think rodents like the pungent smell. Let it and the tissue dry.
2) Decide if you want to use sulfur or other bulb dust prior to storage and apply it. I don't think mice like it either.
3) Store in bags or boxes of vermiculite, or try the Saran wrap method. (Google "no fuss dahlias") Just do a search of "storing dahlia tubers" and you'll come up with 100 different practices and endorsements of each method.

I use styrofoam coolers for tuber protection from mice as well as frost if our power fails. They work well and are really inexpensive or free. Another idea I saw and liked was drilling a series of air holes in a rubbermaid type bin with lid to allow air flow, but no mouse passage. Nice.

I like vermiculite because it is non-drying like peatmoss has been for many, it absorbs excess moisture put off by the tubers, it's inexpensive. Others use wood shavings or even layers of newsprint. You just have to experiment with what works in your area; just keep them from freezing and you've got a good chance you'll save them over winter.