Privet is a popular hedge because it grows fast and is relatively resistant to pests and diseases. It is so robust that in many areas common privet (a native of Japan) and Chinese privet are considered invasive. Pruning this vigorous grower is a must and trimming it is an easy garden chore that can be completed from spring through summer, depending on how formally you want to shape your hedge. Even hedges that have become overgrown can be brought back in line by a persistent gardener.
Trim privets back when planting and each spring thereafter to thicken branches and foliage. Remove a few inches each spring; when the privet reaches the height you want for it, trim it back to that height each spring. Trim new growth one or two additional times until mid-summer, to keep shrubs looking neat.
Shape privets so that they are wider at the bottom than the top in a truncated, steep pyramid shape. Making shrubs wider at the bottom than the top allows lower branches to get sun and rain. Shrubs that do not get enough sun or water on lower branches tend to become spindly.
Trim privet growth up to one-third the length of each branch each spring. Since privets can grow more than a foot each year, the shrubs will still increase in size over the years. Clean out dead branches annually in the spring.
Round the tops of your privets to help shed snow and wind more easily. If the row is long, tie a string to stakes or trees on either end and use a carpenter's level to place it to use as a guide to keep your tops straight from one end to the other.
Renew your privets when they become too large, spindly and their leaf coverage becomes thin. Cut branches down to about 12 inches tall in late winter or early spring during dormancy. The privet will bush out and begin growing again. Trim back by one-third each year thereafter.