People often underestimate the ultimate size of trees and shrubs in their landscape. Many times gardeners and landscapers plant large shrubs too close to homes, driveways, power lines, etc. Plants can eventually overcrowd other plants, block the sun causing too much shade, obscure windows creating security issues and impact landscape aesthetics and curb appeal. I call these overgrown shrubs and trees 'plant bombs' because you plant a tree and it blows up on someone in the future.
People often call and ask how much they can prune away from a plant without impacting its overall health. Tree experts recommend not removing more than 25% of a single stemmed tree at any one time. However, multi-stemmed shrubs usually are not bound by this restriction. Most shrubs can be cut back to a stump and recover.
Overgrown shrubs are cut back in a process known as ‘renewal pruning’. Shrubs can be cut back to 18” above the ground in late winter or early spring to reduce their size. Waiting until late winter or early spring reduces the amount of time that you must look at the unattractive stump in your garden.
Landscape professionals will often do 'renewal pruning' around Mother's Day. They will cut back the shrubs then fertilize the plants to encourage growth throughout the spring and summer. This author has had success cutting back most shrub types including hollies, rhododendrons, azaleas, mountain laurels, spirea, pieris, itea and others.