Pruning of Pyracantha is not technically necessary unless you wish to keep it to a specific height and shape, which if grown as a hedge is usually the case.
When Pyracantha is first planted, ideally it should be left to develop for a couple of years in order to establish a good root system, unless the plant is already mature and you wish to keep it to the current height and shape. Pruning needs to be done at the right time of year however, otherwwise flowering and fruiting could be impacted the following year.
The ideal time for maintenance pruning is actually during flowering in the late spring. This may seem strange, however it is not with a view of cutting back the flowering stems themselves as these will go on to produce the lovely red berries. Pruning whilst flowering allows you to identify the stems that aren't producing and to cut those particular stems back by around a third or a little more to encourage healthy growth which will then produce the following year. When cutting the stems, cut at a downward angle so that any water can run off the cut and the plant can heal quickly.
It is also important to maintain good airflow around the shrub so that disease can be prevented for the most part. To ensure good airflow, don't allow the centre to become too dense. Simply look for the older stems coming from the centre and trim a few (not all) of the stems away to improve the air circulation around the plant. In the main this will help to prevent diseases such as scab or any fungal diseases from taking hold.
Finally, to maintain a good shape, you will need to trim some of the outer stems but usually only the ones most outward growing. These will be slightly older stems by a couple of years. Lightly trim these back to achieve the desired shape but don't hard prune as it will take longer for the plant to recover and be productive.
If however your Pyracanthat is old, overgrown or unruly, it will stand a hard prune to bring it back to some kind of shaping and can be cut back by as much as half of its bulk. This can be done any time between March and October for best results. Although it may take a little while to recover, being quite a tough shrub it will inevitably bounce back.
Our top tip for Pyracantha pruning though is to invest in a very thick pair of gardening gloves. Pyracantha is also known as Firethorn, a name derived from its colourful nature but mostly the long thorns that adorn this plant but which make it ideal as an intruder deterrent. Care should always be taken when pruning but the rewards are plentiful, especially when the plant is in full flower or awash with a profusion of colourful berries.