They have quite a taproot on them. Much better in the garden with room to grow. Mine get to about a metre tall. And if by 'sunny windowsill' you mean indoors, then definitely not.

I'm surprised the petals press well. They're very juicy and the colour comes out in my experience.

flora.. could they be started this late in the season???

ken

Self sowers germinate pretty much all year round but they flower May, June, July. So if sown now they'd probably not flower til next year. I can't be certain, though since I've never intentionally sown them. They just arrive.

I'll Try and Get You a Photo of a Pressed Petal Foral, I KNOW I Have One Somewhere in My Pressed Flower Box.....

I sprinkled some seeds about 10 years ago and now I have hundreds that I have to thin out every year. The goldfinch love their seeds.

IF They Had Been The Same Size They Would Have Already Been Used......
Not Sure What I'll Do With These, Maybe Try and Find Some That Match At Least One of Them......

I've Now Got a Seedling and have used a Pottery Pot So Now it The Waiting Game....
I WISH I Hade Labeled it As I Have NO Idea What it is......
LOL

If it's a seedling it could be anything as P somniferum interbreeds and you never know what the flowers will turn out like. To keep a strain more or less true they'd need to be kept isolated.