The general rule of thumb when cutting spent flower stems or spikes from orchids is to cut them off at the base. This should be done on cattleyas, cymbidiums, dendrobiums, epidendrums, paphiopedilums, phragmipediums and vandas. After these orchids have bloomed, they will not produce any more flowers on the flower spike. There is no need to leave the spike on the orchid until the whole thing turns brown. It can be removed as soon as the flowers drop and the tip of the spike turns brown. As long as the orchid is healthy and growing conditions are right, it will put out a new spike for the next bloom season.
Amboninsis, Cornu-cervi and Violacia Descendants
Phalaenopsis orchids that are descendants of amboninsis, cornu-cervi, violacia and similar orchids bloom continuously from the same flower spike. The spikes on these phals should not be cut unless they grow too long. If the spike has grown so long that it has become unsightly, it can be cut back to just above a growth node. It can also be removed at the base in the spring to give the orchid a rest and encourage new plant growth.
Some types of oncidiums (psychopsis), such as papilio or butterfly orchid, should not have the flower spikes cut when the blooms drop. These orchids will bloom on the same spike for years. The spikes can grow to 2 feet long. The flower spike should be removed at the base when the orchid is repotted to reduce stress while it becomes re-established. Use a good potting medium that breaks down very slowly to allow as much time as possible between repottings.