"Shiva" wrote:
I don't think there are any nutrients that strengthen
stems. Nitrogen is the main ingredient in any rose
chow, it is for the green parts, but can be overdone
at the expense of the blooms, I think.

If I am wrong I believe someone will point it out.

I thought that potash was needed for healthy stems, but
then again I don't have much in my soil and weak stems
have not been much of a problem. As is typical for my
part of Florida, phosphate is excessive, pH very low,
nitrogen left as an exercise to the gardener.

Mark., I've been known to take a leak next to rosebushes
(nitrogen) and scatter potassium-chloride water-softener
pellets around them (potash), though