Best to call the Botanical Gardens if you are planning to reserve a space for a special event. However, anyone can take photos of anything, (plants, people, sunsets, landscapes, art, lizards, rabbits, butterflies, snakes, quail, owls, hummingbirds, tortoisi, cactus wrens, -anything), all over the Garden. If the quincenera is taking place at the Garden, your employer for the photos should pay your entrance fee as a courtesy. If they don't, bill him.
All those involved in the photo shoot would need to pay for admission. Beyond that, there isn't an additional photography fee like some locations.
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