Question
Why do my roses petals turn brown around the edges before they are fully
bloomed?

Answer
There are a couple of possible reasons your rose has brown edges to the petals. Some roses are prone to what might be called sensitive petal edges. That means they will go brown if they get water on the flowers because they are rotting. Overhead watering is one cause of brown petals edges. Also heat can cause the petal  edges to discolour.  The last thing I can think of could be that the rose has got tiny little insects called thrips. However thrips will show up on the actually flower as the insects are sucking out the juices from the petals. They seem to stay towards the base of the bloom.