Is it just the petals you eat, or the whole flower? I have a vague recollection of seeing squash flowers dipped whole in batter and fried, but I'm sure with calendula you just scatter the petals on the food?
You about need a book (or Google) on which parts to eat. It is different from one to the other. I've eaten day lilies, the flower buds when they are 1/2-3/4 developed, chopped on salad. Also, cooked them in stir fry, very tasty. Have tried some others but some I had no idea. Was surprised at "hens and chicks".
Depends on the flower.