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 — do not. 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 pseudobulbs (bulblike, 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 pseudobulbs, 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 pseudobulbs, 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.
1. UNPOT THE ORCHID
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.
2. PREPARE FOR REPOTTING
Before the plant can be repotted, you will need to trim the roots. Use a heavy scissors or small shears, and have a sharp knife on hand. To prevent your cutting tools from spreading viral disease, sterilize each one by wiping with a cloth dampened with rubbing alcohol.
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 pseudobulbs 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 pseudobulbs and a new lead.
3. REPOT THE PLANT
Choose a pot that will accommodate about two years of new growth, based on your observation of the plant. If you are using an old pot, wash it thoroughly and soak it in a 10 percent solution of chlorine bleach for 30 minutes, then rinse it well. (Clay pots should air out for a few days.) If you are using a new clay pot, soak it in water for a few minutes.
Orchids need excellent drainage, so place a generous layer of broken crocks or plastic foam peanuts in the bottom of the pot. Before you use the potting mix, wet it with boiling water, allow it to cool, and drain it. When placing the division in the pot, position the older pseudobulbs against one side so that the new lead has room to expand. Pack the dampened bark mixture around the roots, firming it with your thumbs as you go. The top of the rhizome should be level with the top of the bark.
To keep the plant upright while its new root system is getting established, stake it securely with a loop of twine or use a “rhizome clip,” a simple device that attaches to the side of the pot.
Put the orchid in a lightly shaded location and mist both the plant and the surface of the bark twice daily until new root growth is evident. Once the roots have penetrated the bark, move the plant into brighter light and resume normal watering and fertilizing.