Posted: 10/10/2014 at 22:59
Jack, Deutzia is July cut back flowering stems to ground level. Escallonia, trim lightly after flowering. Weigela, cut back one or two of the old stems after flowering to ground level. Forsythia will now have the flowering stems on so leave until after flowering in Spring then cut back, do it now you lose the flowers.
The answer is really no you should not, wait until they have flowered but if they are out of hand then cut back about one third, you may miss some flowering if you do that.