I'm debating on whether or not to add dahlias to my garden... I did have some mini-dahlias one year, but they never came back. I was disappointed because they did so well that year and the tubers became absolutely huge, but then they didn't come back the next year. I'm guessing they didn't like the winter cold. Are there any out there hardy enought that they could stay in the ground year round??
Planted below level of frequent frosts in well-drained soil they often come back, sometimes for years. Slugs go for the newly emerged shoots while these are still tiny, if you don't control slugs at sprouting time they can prevent the plants from growing. There are only so many overwintering growing points on each clump, I think if slugs are allowed to gnaw off all the shoots that come from these the clump can do no more and eventually dies.
Note too what Ron mentioned on well-drained soil - Dahlias come from climates where the winter is dry, and when planted in climates with wet winters, the tubers can rot very easily in winter unless the soil is very well-drained
Even dug up and stored in a cool dry place, can result in spoiled Dahlia tubers. I have over wintered mine with reasonable success by deep plantings greater than 30 cm. but even then some rotted or as Ron mentioned, were devoured my our gardens' nemesis...the slug!
