Callistemon linearis (common names: Bottle Brush)

Usually after flowering is the best time,it encourages new growth and helps to keep shrub tidy

I wonder if you should prune it. Perhaps lightly to keep its compactness but I found Callistemon species do not like being pruned. I know sometimes they grow straggly and sideways, but their life is not as long as one would like. They virtually do not need looking after much at all.They like to be well mulched, and they are fairly frost resistant. The colour of the flowers range through white, cream, and green, to mauve, pink, purple, and red. Some give the pleasure of two flowering seasons a year. There are many variations within a species which combined with a readiness to freely hybridise makes for a very considerable collection.there are about 25 species, is endemic to Australia, mainly in the eastern states. Many occur in moist, sunny habitats, but most are adaptable to various garden conditions. They are hardy and quick growing in fairly deep, but light, loamy or sandy soil. Protect them from strong winds. Like many natives, many callistemons will tolerate both waterlogging and dry periods but keep the water up to them in a dry summer to get the best flowering, and well presented shrubs.

I have been growing one of these for twelve years. The only attention I have given it is to cut out any shoots heading too far out from the bush right back to where they meet another branch. I haven't fed or watered it but it seems quite happy. The first winter is the critical time; once it has got through that OK, it seems to cope with anything the British weather throws at it