Hedges are trimmed to shape, produce more blooms and to encourage fuller growth. The ideal time to trim hedges varies among bushes. In general, spring-blooming hedges are pruned after they flower in the late spring or early summer. Summer blooming hedges and hedges that do not bloom are pruned in late winter or early spring before new growth appears. If you missed these windows or if some branches just need to go, the hedges can be trimmed in the heat. Next year, however, try do the trimming during the ideal time for your particular hedge.
Water the hedges well about two to three days before trimming to get them well-hydrated before they become stressed from pruning.
Prune in the evening so the hedge will not be immediately exposed to the hottest part of the day.
Limit the trimming in mid- to late-summer.
Trim diseased, broken and weak branches anytime of the year, including during hot weather. Adhere to the first two steps to help the hedge handle the stress of pruning.