Yes, andromeda (Pieris) can be pruned drastically but it is best done just after it blooms. This gives the plant time to put on new growth and set its buds in the fall for the following spring.  If you are not concerned about flowering, you can also prune it in the fall. Fall-pruned andromeda will still produce flowers, but fewer of them because most of the buds have been cut off. However, after a year everything will be back to normal.

You need to decide which time of the year works best for your particular plant. Sometimes andromeda gets so big or leggy that fall pruning is best because the plant needs pruning more desperately than flowers. Although, start pruning while plants are young to maintain their natural form and avoid the need for corrective pruning later.

You can cut all the branches down to about a foot above the ground or you can cut old branches down to the ground and newer wood to a foot or so. 

Summer pruning is not a good idea because hot-weather pruning stresses the plant unnecessarily.

For more detailed information on pruning, see Purdue Cooperative Extension's Pruning Ornamental Trees and Shrubs.

Courtesy of NYBG Plant Information Service