I live in your zone and this will be my 2nd yr. growing dahlias. I lifted them last fall before frost, because I thought that they were hardy to zone 10. They did really well last summer. I planted them in may, and didn't start watering them until they started coming up. I didn't use fertilizer at planting time -- only 2x's per month during the summer. They seem to do really well here.

Sycamore, read all you can at the various websites.

In a nutshell:
Aim for full sun at least 6 hours a day. The more, the merrier. South or West exposure beds usually do great.
Aim for loamy soil amended with some good organic matter that will still allow good drainage. You don't want to drown the tubers- they will rot. I try to pick out most rocks from the planting holes because I hate picking them out of the tuber clump later!

Mulch over the roots to hold in moisture once they're up and growing.

Here, I water twice a week in the heat of summer. Probably only weekly until it really gets dry/warm. This year's lack of rainfall might alter that a bit.

I use Osmocote for an annual fertilizer once they're up and growing. I tried Mor Bloom last year at intervals, but can't really say if it helped produce more flowers because most of mine were brand new, so there's no comparison to be had.

Protect your early sprouts from slugs- evil, vile slimers of the NW! They will denude a little stalk overnight. I've found them as high up as 3 ft on my dahlias. They did not live to boast about their climbing prowess either.

One way I protect from slugs and cool nights in the early season is to cut off the bottom of a gallon milk jug, place them over emerging dahlia shoots and kind of mound up the soil so the little slimy gang can't get access to your plant at night. It makes a little green house for each plant overnight. I remove them all in the morning so they don't cook in the sun inside the jug. Yes, it is alot of work but it's good exercise for your waist. I finally figured out to KEEP the cut off milk jugs instead of cutting new ones every year. They stack up for easy storage in a garage corner or even outside.

You said, "I'm finally back to a climate where I don't have to dig them up each fall, so I thought I'd give dahlias a try!"...
I would plan on digging them up every couple years at least- they would likely survive if you left them in and covered them to prevent too much soaking during the winter, but the plants will be healthier if you dig and divide. The longer they stay in the ground, the gnarlier the tuber clump gets and more difficult to deal with division.

That's my two cents.
Poochella

Hello again!

I finally got my tubers into large pots (I think it was mid-July!) and was rapidly rewarded with sprouts! I have lots of buds now, one of which is opening. Good grief--do dahlias always then decide to open one petal at a time?! Doesn't it know I really, really want to see its full flower?! LOL! What is open is so pretty (a blue-purple whose name I've forgotten--but tag has been saved!), especially since I happened to set the pots near a lovely pink rose.

Thanks, everybody!! :-)

Poochella--Knock on wood, no slug problems (they've already gorged themselves on everything else), but I had a snail on the fascia board above the second story! Nothing stops those guys, including common sense!

wow- second story slug travel just gives me the creeps! What was he after? I've endlessly wiped slime trails off a big sliding glass door- up to about 4 feet and a window at about the same height. Better to need Windex than to replace eaten plants, I guess.