Annual poppies are the only type I try to grow, and with our weather conditions I'd say that any and all of them would be best sown in fall. Still, I think that the luck of the draw, snow-wise, plays a part in how many survive till spring; bitter cold temps before the snow cover appears may thin the ranks...though this is just a guess on my part.
The standard deep-yellow/gold CA poppies have self sown here for probably 5 or 6 years now, but last year's spring (soil) warmup was so delayed that I didn't see blooms until fall. I've never had much luck with direct sowing poppies in spring. I usually get better results if I transplant them out as early as possible. It seems to me that poppy seeds like the reverse of what we have to offer in our typical spring - cool soil, and cool air. We seem to shoot almost directly to very warm air and hot sun, while the ground soil is still very cold and wet.
We do get self sown seedlings of other annual poppies that do well, so my best guess is that those seeds have germinated the fall prior. I have a newer raised bed that's in full sun now, and planted rather thickly with spring bulbs, so I may try direct sowing poppies in that bed this spring...perhaps its soil will warm up sooner than other beds here.
