"David Hill" wrote in message
...
".............Who will be brave enough to quote a rough figure for the
number of weeks by which one can advance the season by putting cloches
over
selected plants in the garden? ........"

3 to 4 weeks

You make it sound worth extending the season for herbaceous perennials by
that much here in the short-seasoned Yorkshire Dales. I am going to give it
a bash this year.

Franz