Dahlia bulbs

I purchased a pkg of 3 bulbs from a home improvement store, planted and they all came up and bloomed beautifully, still in full bloom. When do I dig them up for winter storage? Just before and after a freeze? Also just bought several smaller plants at garden centers, can I dig up those tubers also and try to store over winter? Some of them got real big and bushy and full of flowers and would love to save them for next year. The ones from home improvement are about 5 to 6 feet tall, others the smaller bush type. Thanks

After the first frost
http://thedahliaguy.blogspot.com/2008/03/plastic-wrap-storage.html
http://www.dahlias.com/howtogrowdahlias.aspx

Not sure what zone you are in but for here in UK roughly about zone 6-7 I always wait till the frost has blackened the foliage, at this point I have to decide either to just give the tubers a heavy mulch and hope the tubers wont die off with real cold frost or use the garden fork and dig them out.

I have treated both these ways and not lost any yet but you will know if you get a freeze top inches of garden soil, if you do, lift tubers.
After the foliage has been frost / blackened, cut the foliage off with a really sharp knife for a clean cut, leave about 2 inch of stem out from tuber, try gently remove some soil, and place tubers upside down in a tray, cardboard box etc, leave them there for several days/ week till all the moisture has run out of stems / tubers, clean off the rest of soil with either your hands or use a bucket of water trying NOT to get more water into the hollow stems, (I usually get all the soil off before this stage) anyway the last thing you do is, get a small bag of Flower of sulfur and pour this into a larger paper bag, drop each tuber into the bag and shake the yellow powder by turning the bag over gently again and again till the tubers are coated, this powder prevents the tubers rotting while in store, you need to keep checking the tubers and cut off any rotting / soft bits.

I then place the tubers (right way up) into boxes of either damp sand (not wet) or compost, you cover the tubers all but the stems, I try to leave about half inch of the tuber exposed with the stems, this way I can see if there is any rot OR new little dark shoots growing at the base of the stems.
IF the tubers go too dry or wrinkly, I give them a mist from water sprayer, never had to sink them in bucket of water but heard other people have done this to plump up their tubers if too dry.

Come spring you will note tiny shoots appear at the tuber /stems, this is the tubers starting back into growth again, you can leave them in box but water them till soil is warm enough to plant out or, pot them up and keep in sheltered place till time to plant out.
Hope this helps you out. good luck. WeeNel.

Thanks to you for your help