The smallest Dahlias i've seen have been on the Swan Island site.
www.dahlias.com
They were 18". They are under the low growing and Dwarf catagory.
Hope this helps

Dwarf dahlias come in all types and colors as I'm sure you know. The shortest are usually the Mignon Singles (daisy-look-alikes to those unfamiliar with dahlias) - they grow as short as 10 - 12 inches and come in a variety of colors. Look for the Topmix varieties and the Baby Red and Baby Yellow if you are interested in Mignon Singles. Check under the Colorado Dahlia Society webpage and click on their growers & suppliers list. Swan Island isn't the only grower out there with Dwarf Dahlias. Anemone and Collarette come in a variety of heights. Good luck.

Are the dwarfs basically the same as the bigger ones? Do they create tubers too? Usually I guess the ones you buy are from seed in the dwarf bedding variety. Will they have tubers that can be saved later in the year? Thank you.

Looking forward to seeing how the "Crazy Love" does - it's supposed to get up to 24", perfect for a low border. I've got several of them going on a southern-facing wall in the backyard. Houston may get too hot, but I plan to set up some drip irrigation to keep them cool and mulch in a few weeks. This was two weeks ago, when they were about 6 weeks or so, taken near dusk.

This post was edited by cagoldbear on Thu, May 29, 14 at 10:54

I highly recommend American Meadows for dahlias, BTW. Their selection is a little low no, at the end of the planting season, but they've got a ton of varieties during the spring.

Here is a link that might be useful: American Meadows Dahlias

This post was edited by cagoldbear on Thu, May 29, 14 at 10:56

I grow border dahlias from seed, but even they get to 18-24" tall. The tubers that the small ones produce are pretty tiny, which makes them more difficult to store over the winter, as they dry out easily. The first year I grew them, I did try to store the tubers, and got maybe 50% to survive? For me it is just as easy to re grow them from seed every spring. (actually I start them in Feb)