Answer: Based on your description it is difficult to identify a definite cause of the problem, but here are a few possibilities. Rose blooms do in fact fade fairly quickly, so part of what you are seeing may be normal. Drought stress can cause the symptoms you described, and insects can also cause buds to be deformed and fail to open.
Roses need a rich soil and regular watering, so it is possible that the plastic and stone mulch is at least contributing to the problem. You might wish to remove them and use an organic mulch which is pervious to both air and moisture instead. The mulch will also help feed the soil as it breaks down. This would help keep the root system healthy.
A top dressing of compost is helpful for ailing (and healthy) roses, and you might also consider fertilizing (either a granular or water soluble) according to package instructions. "A generous inch a week" is the rule of thumb for watering, and this is best a applied by a slow deep soaking than in more frequent light sprinklings. Be careful too to avoid wetting the foliage.
Finally, inspect the blooms very carefully for signs of aphids on the stems or other insects. Japanese beetles may be burrowing inside the blooms, as might thrips which are so small they are nearly invisible. A sharp spray of water from the hose will knock away aphids, handpicking or a neem-based spray will take care of the beetles, and insecticidal soap used according to the label instructions may work on the thrips. The soap is also effective in case of a serious infestation of aphids.
Good luck with your roses!
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