I visited some friends this June in the UK and couldn't believe how extensively they just grow wild in virtually all the fields. This goes for both fields left fallow and even those that had been cultivated and planted. One of my friends in the West Midlands has sent me packages of various colours and flower confirmations, but I have been reluctant to waste them in my yard yet. However, I did buy a potted/flowering Icelandic Poppy at one of the local nurseries nearby and it did well until things started heating up by the end of May. It had several seed pods that I am told will allow them to self seed from year to year. I hope that one will, but it was so beautiful that I figure I will just go ahead and scatter the seeds that I have this Fall when things cool down.
My friend tells me that he thinks that they actually do better if you just scatter them in and amongst the grass along a fence line, or just about anywhere around other plants and shrubs. He says they should overwinter just fine, germinating in the Spring just fine.
I have seen similar magnificent poppies in Italy, France, and Spain. I believe most of them are wild flowers that don't interfere with crops ( please correct me if I am wrong). I think they would work very well here, just sown on top the ground, but if and only if we have sufficient rainfall. I don't know what your rainfall is like, but where I am it usually takes extra water to get European plants to grow from seed. Haven't tried these magnificent poppies, but would like to.