I have fed some flowers to my dragons over the years, but never in a huge quantity. Edible flowers should be used sparingly, just a small addition to salads.
Other than that, definitely a good idea to grow your own as most store bought plants are full of chemicals, from fertilizers, insecticides, herbicides and soil 'fillers' (the fillers are not so much a concern when just offering the flower but more if the plants are placed in cages in pots. The little white soil fillers can be accidentally ingested and cause problems.)
Growing flowers from seeds is you safest bet. You will know what goes into and onto the plant as it grows. Of course avoid using insecticides and use only organic fertilizers that are non toxic. Store bought flowers/plants should be repotted and gently washed then allowed about a week to ensure any chemicals in the plant (from insecticides etc) work out of the plant.
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PHLdyPayne