Cymbidiums - Cool Climate Beauties

Literature references to orchid cultivation in China date back to before the time of Confucius (551-479BC) and it is clear that Cymbidium species were among the earliest cultivated orchids. In China, cymbidiums have come to epitomize elegance, refinement and nobility. The earliest record of the genus in cultivation in Europe dates to August 1780 but it wasn't until the introduction of Cym. insigne that Cymbidium breeding exploded onto the world scene. This species produces extremely desirable characteristics in its offspring; tall erect inflorescences with many flowers held well above the foliage and large long-lasting flowers in shades of white to pastel pink. Selective breeding using this species and the other large-flowered Himalayan, Southeast Asian and Southwest Chinese species has made great strides possible in improving flower count, form, size, extension of color range and blooming season such that these beauties are now generally available from late October through May in virtually the entire rainbow of colors other than purple and blue. However, except for fairly recent strides in warmth tolerance, cool nights (maximum about 55º F) are required to set flower spikes limiting successful flowering of these plants to the cooler parts of the country.

Temperature

While cymbidiums are found in a broad range of environments, the larger flowered species in the background of most modern hybrids grow at higher elevations and prefer cooler conditions. Ideally, a temperature range of 50-80° F suits these plants well although with a little protection they will tolerate near freezing temperatures and can, with additional shade and humidity manage temperatures well into the 90's for short periods. The critical temperature requirements being mid-50's at night in the late summer to early fall to set flower spikes and cool daytime temperatures in advanced bud stage to avoid overheating and bud drop. If your cymbidiums grow like weeds and don't flower, look to insufficient light levels and nights that are too warm during the spiking season.

I grew up about 275 miles north of San Francisco along the California coast and managed cymbidiums out-of-doors year round, bringing them under cover of an unheated patio when temperatures dropped to near freezing. One terrestrial species, Cymbidium goeringii grows at the most northern end of the genus' range and these plants will survive with little protection outdoors in the ground as far north as Atlanta, Georgia where winter nights often dip into the single digits or lower. Recently, great strides have been made in the development of Cymbidium hybrids that do not need these cool night temperatures, mostly through the introduction of Cymbidium ensifolium, related species, and their hybrids.

Light

Insufficient light is second only to improper night temperature in keeping healthy hybrid cymbidiums from flowering. These plants should be given as much light as they will take without scorching the foliage and the cooler cymbidiums are grown the more light they will tolerate. In footcandles, this light level translates to about 5000 footcandles up to as much as 8,000 footcandles, approximately 50% to 80% of the light available on a clear, bright summer day. Bright light improves the color of cymbidium flowers and cymbidiums should be given enough light to make the foliage a clear light yellow-green rather than a dark grass green. Too much light will result in pale yellow foliage and burning will produce dry black spots at the top of the leaf arch. Overall, bright light results in harder, tougher plants with stronger, more upright spikes. I have been told by west coast cymbidium growers that pendent cymbidiums, those whose flower spikes naturally arch downward around the rim of the plant, will evidently produce upright arched spikes if the light levels are too low. Think of this as reaching for the light.

Humidity and Ventilation

The warmer you grow your cymbidiums the more air movement they will need to keep their foliage temperature down. Relative humidity should be around 50% or so. Without excellent air movement flowers are susceptible to Botrytis, a flower-spotting fungal infection if conditions are too damp, humidity too high and temperatures too cool. This fungus thrives under cool, damp conditions - the very conditions cymbidiums love!

Water

As a general rule, pseudobulbs and coarse, thick roots suggests periodic drying but not with cymbidiums. These plants are semi-terrestrials, and with the exception of newly potted plants should not be allowed to dry out. They should be watered often enough to keep the medium quite moist but not soggy. In bright, hot weather this may be every few days and large plants that are well-established in their pots will use more water than newly potted ones. Leaf tip die back is very often a sign of insufficient water as is premature leaf loss from mature pseudobulbs. A mature cymbidium that is watered sufficiently will have very few leafless backbulbs in the center of the plant. A plant with many leafless pseudobulbs and only a few growths with leaves around the periphery of the pot is a sure sign of insufficient water.

Fertilizing

Cymbidiums are really strong feeders and consequently can be fertilized more frequently and with higher concentration than other orchids although high nitrogen fertilizers should be avoided from mid-August through early spring. If liquid or water soluble fertilizers are used, apply at about ½ strength along with regular waterings. Those plants grown in finer mixes can be top dressed with timed release fertilizers like Dynamite applied at about one tablespoon per gallon of pot size at the beginning of the growing season. These timed release fertilizers are general 180 day release so when applied in April they are generally spent by the onset of fall. Paul Gripp of the Santa Barbara Orchid Estate in Santa Barbara California once used the following program for plants in a soil-like mix: May 15 and July 1 apply blood meal, August 1 and September 15 apply a mixture of four parts blood meal, four parts single superphosphate and one part potassium sulfate, October 30 apply a mixture of four parts blood meal, four parts single superphosphate, one part potassium sulfate and one part dolomite lime. Apply a small handful over the surface of a 12-inch pot, proportion accordingly for smaller or larger pots. DO NOT use this sort of program for plants grown in bark mixes as it can easily filter down through the mix and burn the roots of the plants.

Repotting

Cymbidiums do not like to be disturbed too frequently and should only be repotted when necessary because the medium has broken down or the plant is outgrowing its pot (generally every two to three years). The choice of medium is up to the grower as long as it holds water well and provides adequate drainage. Plants should also not be divided frequently as the best flowering occurs when plants are allowed to grow into large clumps. Plants to be repotted should be attended to immediately after flowering rather than waiting until a large batch has finished flowering. The reason for this is rather simple. Repotted plants have been seriously disturbed and this root disturbance takes time to overcome. The earlier plants can be repotted after flowering the longer the growing time before flower spike initiation in the fall.

Plants that will not be divided should be disturbed as little as possible. Remove the plant from its pot, shake off as much of the medium as will easily fall off and then, using a sterile cutting tool, trim off only those roots that are dead or will be broken in potting. Position the plant into its new pot, fill in around the roots with potting medium such that the top of the potting medium comes up about ½ inch up the rounded base of the pseudobulb and about ½ inch below the rim of the pot, firming the mix about the roots as you go. When properly potted, you should be able to lift the plant by its leaves. If potted too loose you risk damaging the tender new root tips as they emerge from the base of the pseudobulb. When dividing plants, it is best to keep five or six pseudobulbs (with leaves) together in each division; never less than three or you risk skipping a blooming season.

Backbulbs

Growing cymbidiums from backbulbs (the old leafless pseudobulbs removed during repotting) is really easy and offers an inexpensive way to increase your collection. During Cymbidium repotting season many growers offer backbulbs of selected plants at very attractive prices. First, remove all the old, dry leaf bases and inspect the backbulb for signs of insect infestation. Once clean, place the bulbs standing upright in either pots or flats in a mixture of fine bark and peat moss or fine bark and sand. The bulbs should be positioned so that their bases are ½-1" below the mix surface similar to potting divisions. Keep the flats or pots evenly moist and a little warmer with nights in the high 50's to 60F (they will sprout even with cool nights but you wait a bit longer). Within a month or two one of the dormant eyes at the base of the pseudobulb should sprout. Once the growth has reached a length of three inches or so roots will form. A strong backbulb should produce a flowering growth the second or third year after potting.

Ron McHatton, March 2009