Repotting an orchid for the first time can be daunting. Although it isn’t a difficult task, it is sufficiently different from repotting other kinds of plants that you may be inclined to put it off. Don’t. An orchid that is allowed to remain in the same pot too long will flower poorly and may even die. There are two ways to tell if your orchid needs repotting. First, your plant may simply have outgrown its pot. For example, if your orchid is one that produces pseudo-bulbs (bulb-like, swollen stems that support the leaves), the new growths will extend beyond the edge of the pot, leaving brittle and easily damaged young roots dangling in the air. Second, the growing medium may have broken down. If it appears sodden and mushy and no longer drains freely, you must repot the plant in fresh medium to keep its roots from rotting.
Unless it is an emergency, the best time to repot an orchid with pseudo-bulbs, such as the cattelya shown here, is just after it has begun to produce a new growth but before the new roots have begun to elongate. As a potting medium, your best bet is a commercially prepared mix based on medium-size chunks of fir bark. If your orchid is the kind that lacks pseudo-bulbs, such as a moth orchid (Phalaenopsis) or a slipper orchid (Paphiopedilum), you may repot at any time, although it is best to do so when the plant is not in flower.
Prepare your work area by spreading out several sheets of newspaper—repotting can be messy. Turn the plant upside down over the paper and thump the sides and bottom of the pot to dislodge it. Often the roots will stick to the pot, making removal difficult. If this happens, use a clean kitchen knife to loosen them. The plant will not be harmed if you inadvertently damage some of the old roots.
Once you have removed the plant, carefully pry the roots apart and shake off as much of the old potting mixture as possible. Don’t worry if some still clings to the roots.
To prevent your cutting tools from spreading viral disease, sterilize each one by heating the blade briefly in the flame of an alcohol lamp or gas stove.
Remove any dead or damaged roots. Dead roots are mushy and light brown; healthy roots are firm and white and have light-green growing tips. Cut off any old, leafless pseudo-bulbs at this time. If there is more than one new growth, or "lead," you can divide the plant by cutting through the rhizome. Each division should have at least three pseudo-bulbs and a new lead.