Another thought about thin stems.

There is a growth hormone in the product 'Super Thrive' that is also found
in alfalfa meal that enlongate the growth of rose stems/canes. My
experience is that this produces weak canes that are easily damaged by wind.

In the case of the alfalfa meal, the fourth cutting each season has the
greatest amount of the hormone. Without doing some research, my memory says
that it is an alcohol.

Tim