I've grown only species Dahlias from seed and in my experience they've done great in the Rio grande valley, but do have to be dug up after the first frost. Any that I've left in the ground never reappeared even after a very mild winter.

jfr1107,

I live in arid country as well and don't water my dahlias more than once per week in the hottest summers (100+). I use a soaker hose and water deeply. It's too late this year, but next summer observe the plants in the morning before it heats up and only water if they appear slightly droopy. Be sure to mulch to keep the ground cooler. Push the plants to their limit. Water in the a.m. to avoid powdery mildew.

I have several different types and sizes planted in the beds on the south side of my house that I leave in the ground year-round. I have a 90% or better return rate.

I had been digging up and storing my dalhias each winter until knee surgery prevented me doing so 12 years ago. To my surprise - all came back up. Many of the same dahlias are still blooming in the garden right now.

Last year we had a low of -17. It is key that the tubers are planted in beds with a southern exposure where heat radiated from the house keeps the ground from freezing solidly.

Hope this saves you some labor!

If you do dig up your dahlias, store then in a dark, dry place for the winter. I'd put them in dry sawdust in a box. Although, as laughingearth says, if you have an area sheltered from the winter winds and stays relatively warm, like the southern side of your house, or on the south side of an adobe wall, you might be successful in having them come back up.

Here is a link that might be useful: Desert Gardens