Farmers who’ve never saved seed worry a lot about doing the wrong thing.
But it’s easier than you think.
Just listen to the seed.
When seed wants to be harvested, seed will tell you.
In this picture, you have strawflowers at every stage of life: fresh buds , in full bloom, a bit past perfect (that you should deadhead if you want more blooms but not if you want seed), and one popping with mature seed.
Can you tell which is popping with mature seed?
I bet you can.