For 20 years I have left my dahlias in the ground over winter. Normally, I do not loose more then 5 or 6. THis winter, I lost 100 out of my 130. I can not remember exactly what the weather was, except that it was quite cold for a couple of weeks from mid December. In November I was laid up for a month with Bronchial pnuemonia and had my foot in a walking cast. NO way I could have dug dahlias, but also, no way to predict that this would be the winter that killed my dahlias. We started out with a long warm fall that suddenly switched over to being really cold and staying frozen for about 2 weeks. I am only about 600 feet above sea level but on a shallow north facing slope. THe plants at the bottom of the garden never got even a ray of sun at that time of year. All my survivers were in the upper half of the garden and appeared to be quite random as to which survived and which did not. Totally unpredictable. I think I will at least dig and save out a tuber of my favorite ones, then perhaps bury and mulch the rest. I was heart broken this year to think I had lost Hillcrest Kismet, and all the mail order places were already sold out of it, but a couple of tubers looked like they might possibly have eyes. I lucked out have two live sprouts coming up. WHewww! Even Swan Island lost a number of cultivers to these early freezes this year, before all their tubers were dug.

If divided they will bloom as well as the first year. As the clump grows & doesn't get divided the plant starts to get lazy & live off the clump & not try to put out blooms to propogate itself, so blooms get fewer, weaker & smaller. Stems suffer, too & become weaker so they can't hold up the blooms. If you leave them in the ground for the winter you could dig them in early spring, divide & replant all in one go -- & have extras to pass around to friends or put in different parts of the garden.

I have been leaving mine in the ground. One year I dug one in the fall and forgot it in a pot under my deck, with no soil or covering, and it survived the winter. I planted it in a pot in spring so it got some warmer conditions before planting in the garden. It bloomed much earlier than ones left in the ground. I dug it in the fall and it made an enormous bushel of tubers. Since that time I have left it in the ground and it blooms earlier than the other dahlias planted as a single tuber, and has a lot of blooms. I haven't divided it for several years. Sometimes because of the cold soil and late start dahlias left in the ground don't bloom at all. I suppose it depends on location and on that particular dahlia. I'm actually considering digging some this fall to try starting them in a pot next spring and get a jump on blooming.

Three things have been found to be successful in overwintering dahlias in the ground above zone 7. Luck (mild weather, hearty tubers, etc.) 2. Mulch (protect ground from freezing down to the clump) 3. Tarping (keep moisture from sitting in the soil, rotting tubers) I've had clumps survive winters in 5/6 (never the ones I had hoped would survive, though), during mild winters and no added mulch or tarping. I haven't bothered prepping for clumps overwintering in the ground, as they optimally need to be dug and divided yearly, anyhow. Mammoth multi-year clumps are scary, often needing pickaxes or chainsaws to divide, with a large loss of tubers. The blooms often start to under-perform after a few years, as well. Each to their own. Try it, and let us know how it worked out for you. Cheers!