What am I doing wrong

I've tried to grow Dahlias several time. Either they don't grow or they just die or don't come back the next year. I live in zone 8b. Should I be digging them up in the fall? My yard where they are planted is very sunny until 5:00 in the evening. Should they be getting more shade? I have them planted on the south side of my deck that gets sun mostly all day. I've order Dahlias from several places on eBay and I've also purchased some from Walmart. Am I getting them from the wrong source. Please help as I love Dahlias but they just don't like me. I want to try again this year but I want to yet opinions first.

Have you planted them and they didn't come up, or did they just grow poorly? I've heard that many Dahlias don't like the heat and humidity of the deep south, but some varieties fare better than others. The Georgia Dahlia Society lists recommendations for varieties that grow well in the south:

http://www.dahliasocietyofgeorgia.com/

Your sun conditions sound good. How is your soil and drainage? They don't like to stay too wet. I'm not a big fan of tubers from Walmart and tend to be leery of a lot of ebay sellers, but typically the issue would be either a tuber that doesn't grow or a mislabeled plant. If those you have purchased have grown, but not well, I would think its either the conditions they don't like or the variety doesn't like your zone. A stressed plant that hasn't grown well is less likely to survive winter, but if you find some that do well, I'd think they would be winter hardy for you (as long as the drainage is good, standing water will cause them to rot).

Best of luck,
Neal

Thanks for the good infromation! The ones I've planted didn't grow well and they did not return this spring so I'm guessing they don't like my zone. The beds I had them planted in are slightly raised and mulched so I don't think they are staying too wet. I'll look at the website you gave me and see which ones do best here.

Thanks again for the information,
Colibrigardebner.