collision with crescendo text

[Stefan Thomas]

Dear community,
in the below quoted snippet, the crescendo -text should have more space.
How can I do it?
I made a trial, but without success.
Here the short example:

\version "2.13.0"
dynalong= {
  \override DynamicTextSpanner #'extra-spacing-width = #'(0 . 0)
\override DynamicTextSpanner #'extra-spacing-height = #'(-inf.0 . +inf.0)
} %unfortunately this doesn't work
\relative c'' { \dynalong
  \crescTextCresc 
  \once \override DynamicTextSpanner #'dash-period = #-1.0
  bes2 \< des \sf c1
}