Secret Weapon for Floriferousness??

Not being one to hide rose hybridizing secrets, I wonder if a dirty greenhouse roof has been advantageous?  As the greenhouse has aged (now 21 years old), the original roof covering has become very dirty and discolored.  It is almost like having a shade cloth over the entire greenhouse.  I had considered replacing the roof a couple of years ago, but when I learned that the cost would be almost as much as the original greenhouse, I decided to wait.  For me, floriferousness ranks right up with disease resistance as being a top trait to select for in breeding.  I have found that seedlings that bloom well in the greenhouse do even better outside.  The photos below are of a few new 2017 seedlings blooming in the greenhouse this year.