These orchids are prized for their sprays of large flowers, used especially as cut flowers or for corsages in the springtime. There are two main types of cymbidiums--standards and miniatures. Where summers are warm (above 90°), only miniatures are recommended, since they are more heat-tolerant and bloom in warmer weather.
TemperatureTemperature is the most critical factor in blooming cymbidiums of either type. During the summer, standard cymbidiums are usually grown outside in semi-shade, where day temperatures should be 75°-85° (or more), but night temperatures in the late summer to fall (August to October) must be 50° to 60° to initiate flower spikes. Optimum temperatures in winter are 45°-55° at night and 65°-75° during the day. When in bud, temperatures must be as constant as possible, between 55° and 75°. Miniatures can stand temperatures 5° to 10° higher than standards and still bloom well. Most cymbidiums can stand light frosts and survive, but it is not recommended. Bring them inside when temperatures dip to 40° in mild climates they may be grown outside year 'round. A bright and cool location inside is best for winter months.
LightLight is also very important for growing cymbidiums. Coming from cool and bright areas in Asia, they need high light but cool temperatures. In many of our climates, the high level of light cymbidiums need is accompanied by high temperatures in the summer, which may cause the plants not to bloom. There are several ways of counteracting this: spray the plants with water during summer afternoons to cool the plants down, shade more heavily, and increase air movement. The maximum amount of light possible, short of burning, should be given to the plants. This means only light shade during the middle of the day, or about 20%, shade. In cool areas (e.g. coastal California), full sun is tolerated. Leaves should be a medium to golden green in color, not dark green. Keep shadier in the winter, especially if in bud.
WaterWater must be provided at all times to cymbidiums. As semi-terrestrials, they need a fairly constant supply of moisture. Since they produce all their vegetative growth during the spring and summer months, they need the most water then. Water heavily during the growth season, keeping the potting medium from drying out completely, and reduce water when the pseudobulbs are completed in late summer. Keep barely moist during the winter.
HumidityHumidity outdoors is usually sufficient during the summer months, except in dry climates. There, evaporative cooling in a greenhouse, or misting outside, is necessary. Keep humidity at 40%-60% during the winter, especially if plants are in bud. Keep the air moving to prevent fungus spotting (Botrytis) from damaging the flowers.
FertilizingFertilizing at the proper time will help cymbidiums bloom. During the growth season (spring through late summer), high-nitrogen fertilizer (like 30-10-10) is used. In late summer, use a high-phosphorus, bloom-booster fertilizer (like 10-30-20), to help form bloom spikes. Fertilize at full strength every week to two weeks. In winter, fertilize only once a month.
PottingPotting must be done about every two years, as the potting medium breaks down, usually in the spring after blooming. Shake all the old potting mix off the roots, dividing the plant if desired. Divisions of green bulbs with leaves must have 3 to 4 bulbs minimum to bloom, bulbs without leaves are considered backbulbs and need special care to grow (see below). Pick a potting mix that will hold moisture well; a medium-grade fir bark with peat moss and perlite is a common mix. Select a pot that will allow for at least 2 to 3 years of pseudobulb growth before crowding the pot, while planning on placing the active growing bulb(s) of the division farthest from the side of the pot. Spread the roots over a cone of the mix in the bottom of the pot, and fill the pot with medium, working it among the roots, tamping firmly. The junction of roots and pseudobulbs should be about l/z to 1" below the top of the mix. Keep shaded, drier at roots but humid, until new roots grow.
Backbulbs may be left on the division to add strength, or removed to propagate. Take single backbulbs, and bury halfway in a bark or peat/sand mix. Keep shaded and warm until new growth sprouts, and pot as above. It may take up to three years to produce a blooming-size plant from this method.
Prepared by: Education Committee, American Orchid Society