At this point in the summer, it is very late to be planting dahlia tubers. I would find a nursery that has them in bloom already and plant them in your bed. Dahlias love the sun, so I am not sure about afternoon sun. I would see how they do, and if they do well, plan on getting dahlia tubers in the ground around mid April next Spring

Dahlias probably can't be over-wintered in your area. If you get frost in the ground, you shouldn't leave them in over the winter.

Of the 43 varieties I grew this year, they took between 8 and 84 days to grow enough to get above ground. The average was 31 days. You wouldn't want them to be above ground while there was still frost in the air (this gives you and idea of when they can be planted in the spring.)

They should start blooming between 90 and 120 days after they're planted.

Each variety should describe whether its an early or late bloomer (or neither.)

They'll then bloom until frost kills the stem. Then can then be lifted, stored over winter, and the tubers planted out next spring. Alternatively, you can take cuttings in the spring...see my propagating dahlias photo set:

{{gwi:645224}}

Cheers,
Russ