In this video from This Old House, Roger explains why pruning with electric shears can inhibit interior hedge growth, and how to repair the damage with pruning shears.
1. Pull back outer branches to access the inner recesses of the hedge.
2. Use bypass pruning shears to snip away branches and create openings for sunlight to reach the inner branches.
3. Work your way around the plant, judiciously trimming a few branches from the top, middle and bottom.
4. Trim tall shoots where they join a branch inside the hedge; don't trim them flush with the top.
5. Trim away about one-third of the hedge per year for three consecutive years.