Dare i cut back my forsythia to main part when it has flowered?

You should cut Forsythia back after flowering as it flowers on previous years growth, so if you cut it right back this year you will have no flowers next year! Which is fine if you can wait another year for the flowers, i cut mine right back last year as we had a new fence going in and have only a few flowers this year, but next year should be a good show, so it depends if you can bear to be without flowers for a year!

prune it as soon as it has finished flowering. any new growth this season will have flowers next spring. i renovated a 10' one when we moved here. i cut it down to about 3' tall and it did well for years until the honey fungus got it :o(