Trimming your hedge in July gives you a long lasting effect. Most plants in our temperate climate will grow about 90% of their annual growth during May and June. We know this so it may effect the time you trim your hedge. A hedge should be trimmed many times per year to keep it thick and healthy but for the rest of us who don't want to be trimming that often we can time it for just after its main growth phase. So if we trim in mid July we are not going to see much growth come on after that trim until next May. If I trim in any time in the spring it will be before it grows so may need a trim again in just a few weeks. Older trees/hedges may benefit from an early trim because early pruning can stimulate new growth. Anyway I hope this information will save some work for someone who prefers fishing!