On 12 Apr, 17:20, Stewart Robert Hinsley
wrote:
In message .com, Ed
writesI am told the best time to do this is just after its flowers have
fallen (a couple of weeks time?)

Is this correct, and how severe can I be? I'd really like to get it
back to a bush sized about 6 foot tall, but it has grown about 10-12
foot tall and takes up a whole corner of the garden

cheers for advice
Ed

The usual advice is to cut out a proportion of the stems at their bases
each year. So, if you cut out a third each year, in three years time
you'd have a bush about 6 foot tall.
--
Stewart Robert Hinsley

What my old mother used to do was to cut forsythia any time after Xmas
and bring it into the house in a vase, it would then come into flower
after a time, when it was finished it was thrown out, though some
stems were showing root, by doing this several times each year the
bushed were always kept in hand.
David Hill
Abacus Nurseries
PS you can also do this with ribes