Hi Sandy, Roses are a wonderful treat for parrots, assuming that the plants and blooms have not been treated with chemicals. Magnolia blossoms are not listed among the edible nor the non-edible flowers on any of the many lists that I found while researching the article below. Unless you are SURE that it is edible, do NOT feed it.
Flowers are a wonderful addition to the diet of our parrots.
It is a natural food for them in the wild. They eat many parts of the flower from the new bud to the pollen, petals, and stem. My birds particularly like Hibiscus blossoms which are plentiful in south Florida. Our parrots are likely to get trace minerals and vitamins in flower blossoms that they do not get from their regular diet. The visual impact of a large colorful blossom is obvious when your bird sees it in his dish or cage.