There's no instant cure for an over-grown hedge. It takes hard pruning and a few growing seasons to bring it under control. But there are ways to do the job while keeping the hedge healthy.
If the hedge is too dense, cut it back to the main stems on one side only. Let the hedge recover and put forth new growth for a year. Then cut back the other side.
If the hedge has become too tall, cut back every second shrub to within a few inches of the ground. A thicket of new shoots should sprout around the severed trunks. Then cut back the remaining shrubs the following year.
Don't prune a hedge into a vase shape, wider at the top than at the bottom. The lower part will be shaded, and the foliage will fall off while the upper growth spreads. The result will be a leggy hedge. Instead, prune so that the base is broader than the top.
Note Privet, yew, holly, berberis, forsythia, roses and spiraeas respond well to hard pruning.
