Secondly, make sure the flowers are free of chemicals. Do not buy flowers for cooking from a flower shop. These flowers have been sprayed to make them last longer. If you buy a potted plant from a greenhouse, wait several weeks before using the flowers. These plants are often given growth inhibitors so they dont outgrow their pots. If you buy flowers at a farmers market or grocery, check with the seller to make sure they havent been treated. Also check for bugs on any flowers you buy or get from the garden. Flowers should not be washed. Just brush the insects away.
Lastly, the flowers should taste good and compliment the dish they are added to. Just because a flower is edible doesnt mean it tastes good. Several species of plants have varieties with tasty flowers and other varieties with edible yet bitter flowers. Like other aspects of cooking, always taste your ingredients.