They like the Mediterranean climate we have here in California. It's dry during the summer months.
I got them in my garden by digging up a clump from a neighbor's yard and putting it in a container and setting the container where I wanted the poppies. I only watered it upon planting. It burst into bloom and set set seed and then died. I had poppies growing in that area the following year.
Now, when I dead head the seed pods before the second flush, I just throw them where I want poppies in another part of the yard. Often I only get a few plants the first year, but I get lots more the next year.
I have found they do better with some watering periodically, but not deep watering and not often. They have actually become rather invasive on the house pad level.
I figured that if I had to have weeds, I might as well have weeds that I liked.