Hi yjing, I have had this problem this year also, lucky I have loads of these poppies and not all were affected, some on the same plant were and the rest of the buds opened up and were truely lovely, I can only think that I had a really hot spring and had to water my beds/borders in March/April, then had a really cold wet spell of weather, so I asumed the buds just rotted due to the dry then wet climate, I dont normally have any problems with any poppies, so that was the only change of treatment to the buds that I can come up with, I just cut off the brown mouldy buds and will leave the plant alone now till it is time to tidy up the foliage for autumn, by deadheading the bad buds, it will stop any mould getting onto anything else close by them, hope this is of some help to you and good luck with the plants next year, they are as tough as old boots, so dont think it is a major problem you have. Weenel.
It's one of my favorite flowers, but I've had no luck with poppies. Last year I had three nice plants, then we had a spell of wet weather and all the buds and half-opened flowers, then the plants, rotted.
I planted out three plants in autumn; lost two over winter. One plant left... looking good into June, then the bottom leaves started yellowing. The first bud turned all squishy inside, so I took it off. Second bud was nice and tall and big, it started to open with one petal and then just fizzled out, all petals fell off. I've since cut it back to about 2" from the ground, dug it out (nice healthy root system) and moved it, hoping it will do better in a different location. Poppies do not like to be transplanted, but it's my last ditch effort.
They are very hardy plants once established, but I have found that getting them established is the really tricky part.
It sounds similar to what happened with my poppies. There was a big rain and then the buds all sort of rotted. I will take your suggestions about deadheading the brown buds and hopefully next year I will have a gorgeous display.