One of the most common questions about growing orchids is "Should I repot my orchid?" And in most cases the answer is "No." This, of course, is very dependent upon the kind of orchid that you are growing since they are so different in their needs. We'll review potting needs for several different genera in a series of articles.
Phalaenopsis are monopodial orchids, orchids that grow upward from one stem, increasing in height. Roots will continue to grow out of the stem below and sometimes above the leaves. As the lower leaves die you will get a longer and longer bare stem at the bottom. Due to its growth habit, the reason that Phals need repotting is that the medium they are growing in breaks down over time and the roots in the medium will start to rot.
As a general rule, Phals should be repotted every two to three years unless they are in semi-hydroponic culture or some media that does not break down. In that case they should be repotted when the plant becomes too big for its container or is no longer stable in the container.
Wait for the plant to finish flowering, usually in the spring or early summer. Some Phals are almost ever-flowering, so if necessary go ahead and cut the inflorescence off a long flowering plant. Remove the plant from its container and wash off all the roots being sure to eliminate any media attached to them. If necessary, clip the bottom part of the plant off and put it aside for use as a new plant if you wish. Hold the plant and roots up to the new container and determine what length will be about three-quarters into the new pot and then clip all the roots that will be going in the pot to that length. Be sure that you are not trying to push air roots into the pot, they will rot and die if put in medium, leave them to grow outside the new pot.
Any medium you use for repotting your orchids should be soaked for approximately 24 hours prior to use since it will have been dried for marketing purposes. It needs to have enough time to absorb water so that the newly planted roots are not desiccated. Prepare the pot with drainage material at the bottom of the pot, and place a portion of medium over it at the bottom. Place your plant into the new pot and then carefully pour the medium around the roots. Tamp down carefully with your fingers, or a bamboo stake. I like to put bamboo stakes or shish kabob skewers on two or three sides of a plant to hold it in place until the plant has taken hold and becomes established in the pot.
Put the plant in a warmer and lower light position than it had been growing in before to encourage it to grow new roots and then move to its normal position in about a month. You can either put the bottom piece of the plant in a new pot or in an empty pot until it grows a keiki -- baby plant -- and then pot it up.