Prune Phalaenopsis orchids in late autumn when flower spikes turn yellow, the plants have stopped flowering and there are no visible buds. Only prune mature Phalaenopsis with foliage at least 12 inches tall.
The goal in pruning is to coax the orchid into growing a new stem that produces blooms in three or four months. For pruning, always use a sharp, clean knife or a pair of garden clippers to cut the top portion of the stem about an inch above a node, which is a triangular-shaped area on the stem. To prune blackened or diseased leaves, use a sharp, sterile knife or blade.
Root pruning helps the orchid grow strong and healthy. Remove brown, mushy, unhealthy roots with a pair of sharp scissors or clippers. It is best to perform root pruning in conjunction with repotting. Phalaenopsis blooms typically last from two to four months.