Jeff, when I first started growing them back in the late 80's/early 90's I was living in the Finger Lakes region of New York, and they grew like weeds! Most growing instructions for hops suggest that they like "deep, well drained soils". What that statement is getting at is beyond most folks comprehension in that the soil you see when you start digging your planting hole will continue down at least a few feet. These regions have usually been created by some sort of glacial activity and many times are associated with areas of grape production (they also like deep well drained soils)
A few years later I moved back to Ohio and the hops came with me. They still grew like weeds but not like they did in the 'real' soil. We're lucky to have 8 inches of heavy-textured soil above really heavy clay here in NE Ohio. I generally try to dig as big a hole as I can, maybe 3 feet into the clay, and then backfill with blend of the native soil and amend that with as much organic matter as I can. During rainy years you can encounter the 'teacup effect' where the water follows the path of least resistance and fills your original hole creating a soggy condition for your roots, but it's the best I can come up with. The additional digging/excavating will allow some monster roots to make their way deeper into the soil which in turn lessens the amount of additional water you have to supply.
Some additional points that were touched on are also correct. When you provide a good soil environment you can encourage mycorrhizae to inhabit your roots which will keep the microbes happy and in return, they'll help to keep the roots happy. Lively, happy soil makes all parties involved happy!
One other point that some folks overlook, and can sometimes get them in the jackpot, is that you should have at least a 4 foot periphery around each crown so you can keep the rhizomes in check. Usually, at the beginning of your third growing season, you're gonna want to start pruning the crown. Basically you're just digging about an 8-10 inch deep trench/moat all the way around each crown. By doing this, you'll find any rhizomes that are creeping away from the crown as they'll grow outward from the center like the spokes on a bicycle wheel. I've seen situations where they've been grown right up next to a stone wall, railroad tie wall and many other types of fixed obstructions, and that's not good because once a rhizome finds a nook or cranny . . . it's off to the races. This also happens when growers try to contain them with a 4x4 or some other type of border as when they hit the obstruction they end up growing along it due to not having to grow through soil.
Once the trench is dug and rhizomes cut, it's a really good idea to backfill with some nice compost and then throw the soil you excavated back on top. Doing this on a yearly basis makes digging the rhizomes easier and easier each season.
Sorry for the blather but it's worked for me for many years. Hoppy Trails~