The weather has finally cooled here, and I think the dahlias have done all they're going to do this year. The blooms were gorgeous, and I tried a few new varieties, mainly corals and peachy tones that added warmth to my bouquets. My favorite new variety was called Labyrinth - it just kept producing these huge, curly, peachy-pink blooms that seemed almost unreal.
Where we live in California, the winters are warm enough to leave dahlia tubers in the ground, but our soil is pretty heavy clay, and the first year I did it that way a few of the tubers rotted. Last year, I dug them up and overwintered them in our shed. It turns out that the shed actually gets too hot, and a few of them dried up (fussy little buggers, but worth it), so this year I'm going to store them under the house in a cardboard box full of peat moss. It will stay cool and dampish, but not wet - I think they'll be happier there. If you live where winters are cold, or your soil doesn't drain well, here's how to overwinter your dahlia tubers:
1. Make sure you know what plants are what. I use manilla shipping tags and a sharpie to label the plants even before I dig up the tubers, tying the tag to a stem or two at the very base of the plant.
2. Cut the stems 2-4 inches above ground.
3. Carefully dig up the tubers. I use a pitchfork and loosen the soil about 10-12" around the base of the plant before I dig. Even so, I often accidentally sever a tuber. This won't usually hurt the plant, and sometimes, if the severed bit includes an eye, it grows into a whole new plant. But still, be careful while you're doing this to keep the tuber as intact as possible.
4. Brush off the excess dirt and let them dry off for a day or so.
5. Secure labels. At this point, I double check to make sure the labels are secure. I like to arrange mine by color, so it's important to know what's what. If a plant has just a single tuber, or you have a severed portion, you can write the label directly on the tuber with a sharpie or permanent ink.
6. Store in a cardboard box, or a bag that isn't airtight, with some damp peat moss or potting soil.
7. Check occasionally to make sure they're not rotting or drying out (I'm definitely going to check mine this year!)