The tuberous kind of begonia should be allowed to be touched by frost...a killing frost that does in their foliage. At that time you then remove the foliage and dig up the bulb, let them dry for a day or so in your garage or shed, then store them in your cool basement, away from light, away from heat, away from water. Make a note of which end is UP...store them in a way you know which is which. Then in March, bring them out and you can put them ontop of the refrigerator--there they might begin to grow a root. Whatever, pot them up, just barely under the soil surface...their tips might even be seen, water them, give them sunlight and pretty soon a little bit of fuzz shows on the surface....it might look like like mildew...but its not...its the bulb beginning to grow. Keep the soil damp...but not wet. Tuberous begonia is one of the slowest forming bulbs and it might be June or July before they come to sizable growth and bloom. The bloom they produce is worth the wait.

I uses to live in San Francisco and had no problems with begonias growing under a porch. They always bloomed profusely and tubers always got bigger each year. Even the seeds i started in march of 2011 made tubers the size of a baseball. Albeit, we have a long growing season and the right temps. I gave them all up and moved to MA and boy is gardening different. I started with Blackmore and Langdon seeds feb of 2013 indoors in Boston. Those that survived the move outside all created tubers the size of a peanut to the size of a golf all. Out of about 100 seedlings, I culled out about half that did not have double blooms and the next spring, only about 20 made it. I kept them too cool in the basement. None bloomed summer of 2014. Mainly because I used regular topsoil with some weird mulch incorporated. They did all survive and their tubers were slightly bigger. I have started more Blackmore and Langdon seeds.mi started a batch dec 15 2014 and about 100 have been reported into 50 cell trays. I just started another batch last week just for backup. They grew really well when I had them under a 4foot shoplight on a shelf above the stove but started dying and damping off when i moved them to the basement with no bottom heat. My advice is to start very early if you want tubers and enough time to evaluate flowers to cull, being feb a the latestThey generally create tubers in the fall when day length decreases so they need enough leaves and a big enough root system to do that by September. Also give them bottom heat and use a looserepackaged potting mix. I made the mistake of potting them up in whatever was around only to find the the pH of the black mulch I used was close to 7.5

Linnea, Next fall, let your begonia be touched by frost. Much like dahlia, the frost will kill the foliage. That's your cue to bring them in --- to a garage or other place, where they have the stalks removed, flowers go too, and let them dry for a couple days before they go into storage. Just like geraniums, they can be stored where it is cool, dark, and dry. There left to spend the winter. No sprinkling, no water of any kind, no light which can initiate growth, no heat...just cool, in the range of 38 - 50ºF.... AT this time you might make note of the color of the flower on each bulb so that next spring, you can plant accoridng to that wish. If the bulb doesn't have a particular look showing which side is up, put them on a shelf designating which end had the roots. Most times though you can feel the concave end---that's the top. Old roots too can give it away. Now I believe the frost treatment allows the bulb to send its starches and sugars back down into the bulb....much like why we let the tulips wilt on the vine, to do the same. The next spring, the bulb has all the energy that wasn't destroyed by removing the foliage too soon. If the begonia goes inside to enjoy the bloom for as long as it will, then do much the same, remove the foliage, let it dry, then store it where cool. As far as why the foliage wilted, the distinct temperature change from out of doors to indoors, is probably what caused it. Keep cutting back the water and let the bulb use less and let it go dry.

Dahlias are showing up Linnea, they are about 4 inches tall right now, you don´t have to worry about moisture where I live ( central Mexico ) it´s hot and dry and "winter" is just a word, we don´t really know what that word means. From the gardening point of view we only have two "seasons", dry ( Oct -> Feb ) and rainy ( March -> Oct ), or let´s say, from the outdoor activity point of view we do have 4 seasons: pre-spawn, spawn, post-spawn and hunting. Kidding aside, I personally don´t like the saran wrap method, Jan´s method is what I use when I lift to divide the clumps ( every 4-5 years, it takes a 5 gal bucket just to hold the clump ) and they do fine, the wood shavings used for hamster cages is usually cedar. Yes, you close the container with a lid, just be shure to ocassionally take a peep at the tuber to see how they are doing and to feel if there´s no moisture forming inside the container. Divide when you see the sprouts, then allow a the tuber to heal for about a week or week and a half. Do not wash the tuber after lifting, just allow the soil to dry out and crumb appart on it´s own. The enemies of dahlia tubers in storage are: 1.- Moisture ( fungi ) 2.- Low temperatures ( keep above 45° ) 3.- Dryness ( shriveling )