Guess you mean dahlias? If so, they actually have tubers instead of bulbs and it's true they're not winter hardy in Illinois. Let them go until the first hard freeze/frost turns the foliage slimey and black.

Then, dig them up, cut off the foliage, shake or gently hose off the dirt, dry them in your garage or basement, then bag and store in a box. Check on them periodically for mold and rot.

There are some very good step by step instructions with pictures by Googling digging and storing dahlias. And the people over on the Dahlia Forum could answer any questions you have.

They're beautiful and I grew them for several years - generally buying new ones each season since my attempts at storing them were largely dismal failures, or they started to sprout and got terribly leggy months before they could be put outside.

Hi Diluthinbloomz..Thanks for replying. Wouldn't a garage be too cold? Our garage isn't heated, so except for wind protection, temps are about the same as outdoors..
Sorry for misspelling dahlias..
They are beautiful plants with large, lovely flowers. Colors are stunning. I'd like to be able to overwinter, but it sounds like a job..lol. Checking for mold and growth..
It's too bad yours didn't make it. Perhaps they were kept warm or in sun, which caused premature growth, or got wet and molded??? It's been years since I stores bulbs..also there's mice to worry over. which is worse than growth or mold. lol.
Anyway, thanks for replying..Toni

Yes, an unheated garage in zones 4 & 5 would be too cold over the winter but a good place to lay them out on newspaper to dry for a short time after digging. A cool, dark corner of the basement would be best for long term storage. I have a cool cellar closet in my basement which should be ideal - unfortunately for me it hasn't been. Many people have wonderful success, so I'd say it's worth trying especially if you have some nice varieties.

But do check out some of the internet websites for the proper methods of digging and more importantly - drying and storing.

Duluthinbloom, I'm assuming bulbs/corms need darkness when stored, right?
Do you know of a scent that would deter mice? We're not far from the river, and in autumn/winter, mice 'try' invading our house, shed, garage and green house.

How about storage containers? Or would they rot the corms.
Thanks so much for your help. Toni

Yes, darkness is essential. As for mice, no scent would be effective but a plastic RubberMaid storage bin would be.

From the excellent website www.dahlias.net/dahwebpg/TuberStor

put about four cups of coarse vermiculite in a one gallon plastic produce bag. The bag can breathe, and the small holes keeps the vermiculite contained in the bag. Other materials also work well: sphagnum peat moss, wood shavings, or sawdust.

Box the Tubers to prevent light - plastic, cardboard, wood,
or whatever will do as long as the lid can be closed to prevent light (and mice) from getting to the tubers.

An "ideal" temperature for storage would be around 45 degrees and check all bags twice each storage season--December and March. Rotting tubers should be removed.