Q: I have a big barrel of cymbidium orchids, but the barrel is shot, and my clump of orchids looks crowded. What’s the best way to replant it? — Melissa Gilliam, Venice, Calif.
A: Whether you keep it indoors or outside, you can usually count on this popular orchid to grow well for three to six years between repottings. A large plant in a barrel 20 inches or so across should have 12 to 15 flowering spikes, but since your cymbidium is crowded, it probably doesn’t bloom that abundantly. However, merely transplanting the whole clump intact to a larger container is not the remedy. Your orchid needs to be divided. The time to do this is right after the flowers fade in spring. With luck, you’ll then have two or three cymbidiums large enough to flower well next year. Unless you plan to hold a plant sale, resist the temptation to make multiple smaller divisions. Meager divisions won’t bloom again for at least two years, and potting is a lot of work. Big cymbidiums look best, and that means big pots.
For this first division, a 12-inch pot is just right. Cymbidiums are deep rooted, so use standard pots (as wide at the top as they are tall). You’ll also need a fresh potting medium. Don’t reuse the old mix: By now, it will no longer drain as it should. Recycle it through your compost pile, or use it for mulch. You can find ready-made cymbidium (or semiterrestrial orchid) mix at a good garden center or in a mail-order catalog. Or you can mix your own, using equal parts fine- and medium-textured fir bark. Add enough #2 perlite to make up about 15 percent of your final mix.
Now for a close look at a clump of cymbidiums. After flowering, a bulb (technically a pseudobulb) generates one or two new shoots from its base. A shoot reaches full size by the fall and flowers a few months later, typically in the spring. That shoot will never flower again, but it does make one or two shoots of its own. By about its fifth season, it becomes a leafless backbulb carrying dormant buds. So each clump has one or more leading shoots, connected to older bulbs by short, horizontal roots (rhizomes). Just inside your barrel is a tangled mass of leading shoots looking for a way out. The center of the plant is likely full of backbulbs, which you can either discard or repot to start new plants (in two years, they’ll attain full size). Pull the rotting barrel staves and bottom away from your cymbidiums, and you’ll expose a mat of roots covering the potting mix. Using a 10-inch serrated kitchen knife or a sharp machete, slice a 2-inch section off the entire base. Next, poke out of the center any bark mix that comes away easily, and shake the clump gently to free more particles of bark. As you work the mix loose, look for places where you can break apart the clump. When you encounter a leafless backbulb, cut (or snap) it off. Once you’ve reached the center, the clump will separate more easily. You want to end up with at least two clumps of three to five green, leafy pseudobulbs and their roots. Each clump should be roughly 6 inches across, leaving about 3 inches of space between the clump and the sides of its new pot. The bases of the pseudobulbs should rest about 1 inch below the rim. Center the clump in the pot and place growing mix around it, really packing it in to insure that the plant can’t wobble. Then give it a good soaking. The first month after repotting, keep the plants out of bright sun. Water them at least every other day (don’t worry: Fresh mix is so porous, it’s almost impossible to overwater). After three or four weeks, begin watering once a week with dilute liquid fertilizer. Or sprinkle time-release fertilizer (most compounds are good for at least three months) on top of the medium.