loss of color in zinnias

Why do my zinnias lose their vibrant color after planted? This is Phoenix, AZ. Some of these plants are in direct sunlight while others are in partial shade. I planted them with a good depth of Miracle Grow potting soil but in the ground. I have fed them about every ten days. They get watered once a day about four A. M. BTW, I have the same problem with daisies. Other flowers, herbs, vines and all the annuals do extremely well. I get deep purples and vibrant yellows.
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Could be the extreme heat and sun drying out the flowers. In GA when it gets into the high 90s my roses bleach out to a lighter shade

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My zinnias bleach out too, after a while - I think it's just a natural phenomenon.
BTW I wouldn't feed annuals as much as you say you do. The trick with annuals is to keep them anxious to flower as much as they can, so I keep my soil as lean as possible.
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