Prune after Bloom is the general rule to follow with all flowering trees and shrubs. Right now is the time to prune Andromeda (Pieris). Clip all the spent flowers off and cut down any awkward tall growth and fertilize with Holly Tone to encourage bushy growth and next year’s blooms, which will form in early summer.
Other spring bloomers to prune after bloom: Magnolia trees and flowering crab apples, mountain laurel, Rhododendron, and Azalea varieties, Forsythia, mock orange, flowering almond, and bridal wreath Spirea (Spirea x vanhouttei ) and Spirea ‘Mellow Yellow’ (Spireae thunbergii 'Ogon').
Exception to the prune after bloom rule: Dogwoods, Redbuds, Bradford Pears and Pee Gee Hydrangea can be pruned while still dormant, in late winter or early spring, because it is easier to see the structure without flowers or foliage.