Lots of things can affect whether a Dahlia blooms. That it did at all usually means its viable. Ask yourself:

When did you plant it? You should have been able to plant it in mid to late May...whenever the ground is no longer frozen. If you planted it later, that could explain late blooming.

Did the stem break at any point? I had a Lemon Tart that was coming into bloom in late May (I started it inside in January.) Shortly after it was planted out, one of my dogs decided it was in her way and broke it at the ground. It finally recovered and bloomed 2 weeks ago.

I'd go ahead and lift the tubers and give them another try, earlier next year if you can. Might also want to check your soil. Take some into a garden center and ask them if its good for tomatoes...if not, Dahlias won't like it either and may not do as well because of it.

Cheers,
Russ

I'm with Russ on this. I give any variety at least 2 years' trial before tossing it. Good advice to try starting your tuber early next year and see how/when it blooms. Seems silly to waste the space for one flower that shows up just days before the season's over.

"Ripples" got two years in my best sun and still didn't bloom til October- out it goes. Some just bloom later than others no matter what you do.