When should I prune spring-flowering deciduous shrubs?

FAQ
Question: 

When should I prune spring-flowering deciduous shrubs?

Answer: 

Spring-flowering shrubs, such as lilac and forsythia, bloom in spring on the growth of the previous season.  The plant’s health or condition determines the best time to prune spring-flowering shrubs. 

Neglected, overgrown spring-flowering shrubs often require extensive pruning to rejuvenate or renew the plants.  The best time to rejuvenate large, overgrown shrubs is late winter or early spring (March or early April).  Heavy pruning in late winter or early spring will reduce or eliminate the flower display for 2 or 3 years.  However, rejuvenation pruning will restore the health of the shrubs.  

The best time to prune healthy, well-maintained spring-flowering shrubs is immediately after flowering.  (Healthy, well-maintained shrubs should require only light to moderate pruning.)  Pruning immediately after flowering allows gardeners to enjoy the spring flower display and provides adequate time for the shrubs to initiate new flower buds for next season.