NoH2O wrote: I have grown Shirley poppies for over 40 years both in the Midwest and the Pacific Northwest. In my experience they do keep blooming when deadheaded. The blooms are not quite as large and the stems are a little shorter on the later blooms, but they remain lovely. As a bloom loses its petals, I cut the stem just above the next leaf node (where there is often a bud forming already).
Like all annuals, the poppies think they have finished their life cycle once they produce seed and they begin to die.Therefore, they will last much longer if you deadhead them. Also, if you let them reseed themselves they will eventually revert to their original red color. I find it best to use purchased seed every year. I never use all the seeds in a packet in one year and they will continue to be viable for at least a few years.
If you want to use them as cut flowers, you have to seal the ends either by immersing the bottom inch of the stem in boiling water for about 25 seconds or burning the stem end with a candle flame. They don't last long when cut - 3 days is about the maximum but they are so amazing to look at that I think they are worth the effort. I usually cut them at dusk (cut only the buds that are just beginning to show a trace of color and whose stems are straight up), seal the stems and then keep them overnight in water in a cool place - the cooler the better - to condition them. After arranging, keep them out of direct sunlight and in as cool a place as possible.
Then, sit back and enjoy!
There are a few Papaver somniferum mixed in but the majority of poppies in these pictures are Shirleys. The pictures were taken in early June.