Wait until mid March, then start the tubers off in 5" pots of moist compost. The tubers should be planted so that the stem is well clear of the compost....do not bury them.
Dahlia tubers start to grow when soil and air temperatures reach 50'f. If you read my blog you'll see how they grow and how you can take cuttings, but a lot depends on what you have bought as to how to grow them in your border and how many.

Do look at Scrumpy's blogs - he's a fantastic dahlia grower!

Thanks...where do I find the blog?

Andrea click on Scrumpy's name, it will take you to Scrumpygraham's Profile, in the boxes click on the blog box which bring up the list of his blogs and go from there, his Sweetpea ones are good as well...

Thank you :-)

Wow..just had a quick look at the blogs, your dahlias are amazing!! The blog is great...very informative. I don`t have the heat in the greenhouse unfortunately, so will maybe start them a little later or as suggested try some on a sunny window ledge.
I love the semi cactus varieties in your photos, and seeing as one is called Ruskin Andrea, I would love to give that a go, where would I get some tubers from of the varieties you have shown, or am I aiming too high and are these difficult varieties to start with, are there ones that are easier to nurture than others?
Thanks

Ruskin Andrea is a nice one to grow.
As is Ryecroft Zoe.

All dahlias are grown the same way whether they be exhibition quality or garden centre quality. Biggest difference is that the blooms will always be better from the exhibition ones,and how good they are depends on how you grow them.
As to availability, your best bet is to go to a specialist supplier and ask them to send you plants in May.

I use http://www.eurodahlia.com/

and http://www.hallsofheddon.co.uk/

Both have the above.

Thanks again, you have inspired me.