| Forsythia flowers on stems and buds made in the previous year. If you prune Forsythia too late in the year, then you will be cutting off the next spring's flower buds and flowering stems! Forsythia needs a long growing season in which to make its flowering stems and flower buds for the next spring. If you prune Forsythia too late in the year, then you will be pruning off the flowering branches for next spring. For normal Forsythia shrubs - bushes - you will need to prune them as soon as possible after flowering in the early spring. If this is done, then you will have masses of flowers the following year. Pruning Forsythia. Right after flowering, cut out all of the stems that have flowered - back to a good healthy pair of buds. Depending upon how vigorous your forsythia variety is, the pruning cuts may be from between 12 in (30cm) to 2ft (60cm) in length. At the same time - with an established shrub, it is a good idea to cut a few stems back down to within a few inches (cms) of the ground - say one out of every three stems pruned this way. This will encourage basal shoots to grow, which will keep the Forsythia well provided with strong stems to flower in later years. 
This is a typical Forsythia stem that would be pruned out right after flowering has finished. The pruning cut would be right at the bottom of the picture. The stem will then re-grow during th year, to the same length as before.
Basically >>> a/ Cut back flowered growths at least 1/3rd of the way back into the shrub, to a new young shoot; or a strong bud (Leaf joint) b/ Cut some of the growth - about 25% - right back to within a few cm of the ground. This will produce nice basal growth, which in turn will be part of your framework for the following year. If you don't do this, then the shrub will simply get taller each year, with the flowering growth right at the top.  Pruning cuts well back into the growth. |  Don't forget the lower cuts to force some basal growth. |
Forsythia Hedges Forsythia make good dense and colourful hedges, that can be kept well under control for a small (3ft) 1m high hedge - or as a larger hedge. If you want a well clipped hedge of Forsythia, the pruning is carried out with either a pair of shears or a hedge trimmer. The hedge can be cut twice each year, with the last cut taking place in Late July/August. 
As can be seen, you can prune forsythia to make neat shapes as well as hedges!
Providing that the pruning is a light trim, and not back hard into the stems, then there will be plenty of flowers the following year. If the hedge gets too 'open' then don't be afraid to prune it hard in Early Summer. It will soon send out a mass of new shoots with which you can re-form your hedge. Thereafter, prune as above. Forsythia suspensa - groan as a hedge - should only be pruned the once, to allow plenty of long arching stems to form an attractive - but slightly informal hedge. Back to A-Z of Pruning Shrubs | 
