Good morning from Perth Australia, i have the same issue here in Australia. It started about a few days ago and my tree is dropping brown flowers. We have been fertilizing it for years, it is has grown more than double in size. Leaves looking great, no bugs, roots in tip top shape and leave thriving too? I am puzzled and you all might be able to help. What was the outcome from 2012; the original post? Thank you so much ; will post a picture below. many thanks christina

In my experience weather can affect the blooms to the point of them dying before having a chance to mature.. A very dry wind should be able to dry them out before opening. My MIP suffers from such events a lot. It might be a reaction from the rose itself conserving humidity or energy under adverse conditions. Less established / mature roses tend to suffer more. But it would better if somebody more accustomed to your kind of weather chimes in.

Pictures please. One gallon pot, It might be to small and young.

This is much more common in fruits like apples than roses. Basically the plant decides it has more flower buds/fruits than it can support, and spontaneously drops some. It isn't usually considered a bad thing since fruit growers will often thin young fruit to improve the size and quality of what is left. It isn't something discussed much with roses since few roses do it without an enormous amount of stress. Rugosas are one of those roses. What you can or should do about it is more than a bit of a mystery. I will say that rugosas are much finickier than most people give them credit for. They like acidic sandy soil, and struggle in heavy soil, or neutral or alkaline pH. Since some of the leaves in the pictures are beginning to show signs of chlorosis, I'd start with a standard soil test. It is possible they were originally planted in soil that had been pH adjusted in some manner, and that treatment is wearing off. I have this issue with roses with multiflora heritage. However, you really need to establish a base line reading before messing around with things.