I don't think it is too late at all! even if you don't get much of a head start, most of the growth occurs once they hit outside in decent temps anyway.

My inlaws live in a zone 3 or 4, (depending on what map you source / who you talk too, a lot o f people think that their town is in a warm bubble in Zone 3) But anyway, they always just direct sow Dahlias mid / late May and have fabulous flowers!

Yes, like homemommy says, it's certainly not too late. I usually don't pre-start my dahlias because I don't have the room, and I still get plenty of blooms - just not as early as I probably would if I did. In fact, the ones I have ordered for this year have not yet been delivered (I'm borderline zone 5). The only risk you have in ordering this late is suppliers being out of the ones you wanted. As far as growing goes, it's not too late at all.

I had alot of rot last year and had to get tubers as late as July. There were still some growers out there with dahlias.