Digging up Dahlias

I want to dig up my Dahlias and split the rhizomes fro next year, when is the earliest I can do this? this is my first year growing Dahlias

Well, we wait til the first frost when the plants get bitten and the plant droops. This sends a signal to the dahlias that it is time to put energy into the tubers in preparation for winter.Wait a few days to a week, then dig them. Not sure how this would be done in Spain as I am not sure you ever see frost. DG'ers down south. When do you dig yours?

Thanks Oberon, we get light frosts here so I'll look for the droop!

Yes. Mine turn a yukky sort of grey and rather than droop, they really wilt! What are your average winter and summer temps?

Our average is low 2 - 4 high 35. Would it be OK to put the saved rhizomes straight into compost?

Not compost. I believe they would rot. We wash them well with a garden hose usually, set them upside down on a screen to dry for about 24 hours. I try to dust them with a powdered fungicide if I can find it, then wrap tightly in plastic wrap. Sounds nuts and there are other ways to do it, but the plastic wrap keeps them from dessicating, and if one rots it doesnt effect the others. Just be sure they are dry; get the dirt out from between the tuberous mass as best you can, then dry; they can dry a day or so, depends on your air moisture and temp; just don't let them shrivel. Then the tricky part. They need to be stored between 45-50 degrees or as close as you can get and in darkness. They will start to send out shoots (at least here they do) in early March. You should take them out and put them up, or put them in your garden if there is no danger of a frost. Actually, since they are pretty much underground, that might not be an issue.

Biscombe - if your low is pretty much just around freezing, with just a few days below that, the tubers will do fine in the ground throughout the winter. You may want to try digging up your rhizomes, split them, and then put some back into the ground (maybe letting the cut surfaces dry 24 hours before replanting), and then store some (or give away to friends). I tend to take the easiest way out, and often leave my tubers in the ground since I live in what we call zone 9a - we get about 10-15 days below freezing, and the ground NEVER freezes (except maybe the first couple of cm during an extended freeze). I am trying the digging up and dividing every two year routine. I have only been growing dahlias about 4 years, and though I do lose a few that I leave in the ground, I lose more when I try to store over the winter in the garage. I am not one to look at them once in awhile to see if they are still moist. The ones I leave in the ground sprouts when the weather is warm enough ( and bait for snails - they are voracious in early spring) and they bloom weeks before the ones that I store. But, check to see if your ground freezes or not before trying that.

I have Mediterranean type climate - similar to yours?

Soils, I never even thought of that. Duh....of course, I never leave dahlias, begonias, glads in the ground at all as they would freeze to a rock. thanks for chiming in. I would have felt badly giving wrong advice and having them lose their dahlias.