GROWING THE NEW
by Milton O. Carpenter
Because of the diversity of habitat among the genera and species of this family, it is important to know something of the climatic requirements of the species involved in these hybrids. For example, Oncidium onustum occurs at sea level at the Equator in South America, often in full light and on fence posts, while Odontoglossum crispum is found at 9,000+ feet in the Andes mountains where it is continually cool and moist. What follows then are recommendations for culture of the "Temperature Tolerant" oncidiinae which we have created at Everglades Orchids. These special plants are created to perform well in temperatures from 55F to 100F without the necessity for a wide temperature variance between day and night temperatures. In most cases we have incorporated a warm and a cool parent to produce the required tolerance of temperatures at either extreme. While the various cultural factors will be discussed individually, it is important to remember that they are all closely inter-related. For example, when temperatures and wind movement are high, additional humidity and moisture is required.
Seedlings prefer filtered or diffused light of approximately 1,500 to 2,500 foot candles while mature plants will enjoy from 1,500 to 4,000 foot candles. In Florida, 60% shade will result in about 4,000 foot candles of illumination on a bright Summer day. A good indication of proper light is the color of the leaves\; they should be bright green as opposed to dark green (too much shade) or reddish green (too much light). I have often moved a plant which was large and strong, but which had not bloomed, and putting it into brighter light conditions watched as it responded almost immediately by sending up bloom spikes. Care must be taken when doing this, however, that the increased light is not too great or injury to the leaves will result. Once spikes are initiated, it is important to leave the plant stationary in its relationship to the light source, else crooked spikes and erratic flower presentation may result.
If your temperatures are seldom above 100F or below 55F then our "Temperature Tolerant" hybrids should perform well, however if you are really HOT or very COLD and can't do anything about it then a little research is suggested. For example if you live in the "Sunny South", Odontocidiums which have Oncidium's maculatum, sphacelatum, wydleri, or hyphaematicum will probably perform well, whereas those with Oncidium's macranthum, incurvum, or tigrinum will probably not do so well. Our "Temperature Tolerant" hybrids regularly withstand daily high temperatures of 100 F. for five months in our Summertime. See our article in the AOS Bulletin, January 1994.
The species utilized in these hybrids generally enjoy relatively high humidity in their native habitat during most of the year. In cultivation a range from 50 to 90% is considered favorable, with seedlings usually preferring 70% or higher. Generally humidity should be increased as temperature, light intensity and air movement increase. This can be accomplished by misting the plants and "damping down" the greenhouse floor periodically. Do not mist the plants late in the afternoon however, as the foliage is more susceptible to fungus and bacterial infection if not dry by nightfall. During Winter months, if artificial heat is employed, maintenance of proper humidity levels should be considered. If plants are kept in the home, they will benefit from being placed on a saucer filled with small pebbles and water (in bottom of saucer), this will increase humidity around the plants as the water evaporates.
Good air movement around the leaves and the bottom of the pot seems a good rule to observe as long as the humidity requirements are met, thus preventing the possible desiccation of the plants. Adequate air movement reduces leaf temperature allowing higher light intensity and more vigorous growth. An additional advantage is the reduction of fungal and bacterial infections which a high humidity alone might otherwise cause.
Oncidiinae intergeneric hybrids should generally be kept somewhat moist. Never allow them to dry out completely but be sure to allow for excellent drainage as they do not appreciate soggy or waterlogged conditions. Generally, they require more water when making new growth and less once the bulb has formed. When watering be sure to water copiously, to ensure a thorough wetting of the potting medium and reduce the build-up of toxic minerals.
A factor often overlooked and of prime importance. City water and well water will many times be found to contain an unusually high total soluble salts content (the relative amount of all minerals dissolved in the water). Ideally the total salts content of your water should be 50 P.P.M. (parts per million) or less and not more than 100 P.P.M. If you are not sure what your water contains ask your county agricultural agent for guidance. If your water supply is poor, consider catching rainwater (provided there's no acid rain in your area).
Repotting every two years seems to be a good rule (sooner where water quality is poor) except for those plants in "rock wool" or mounted on tree fern slabs, or cork bark - which should be repotted only when the media starts to break down or the plant has outgrown the slab. If plants are potted in spaghnum moss they may need to be repotted each 12 to 18 months. Plastic pots offer these advantages: economy, keeps potting media moist longer, does not build up "salts" on the inside of the pots, easy to clean and sterilize for reuse. Clay pots offer these advantages: better air movement around the roots, heavier "base" for plants with tall spikes, and evaporation creates a cooler root atmosphere. Usually, these plants should be repotted when the new growth is two or three inches tall or when the new roots first appear. Remove any organic mix and trim off all dead roots. If it is necessary to divide, keep at least three to five mature bulbs together. Water the newly repotted plants lightly until the new roots have penetrated the media, then resume normal watering. Pot size will depend upon the size of the plant and it's root system. We generally use small, shallow pots allowing room for an anticipated one or two year's growth.
Basically, any mix which has good water retentive qualities while still open and allowing good air movement through the media can be used. Our preferred media is "Rock Wool", an inert material made from molten, spun, rock. We are using Grodan "Stone Wool" with 1/3 expanded perlite added and have had excellent results. The obvious advantage to this material is that it will not "break down" and thus can be left on the root system indefinitely if particular attention is paid to "flushing" with pure water routinely for accumulated salts. I have observed these integeneric hybrids growing well in New Zealand spaghnum moss, straight tree fern, straight fir bark, and all sorts of combination mixes! The key is that they do not want to become completely dry between waterings, preferring instead to remain at least slightly moist at all times, and yet must have good drainage. Recent experience has shown that the Brazilian Miltonia's and primary hybrids with them do best for us in straight charcoal (fingernail size).
Moderate feeders, these plants will respond to a balanced fertilizer (such as 20-20-20) at one half strength, every second or third watering. If potted in fir bark, a high nitrogen fertilizer (such as 30-10-10) will be required. Feeding can be generally increased during warmer weather and when plants are in active growth, while the reverse is true in cooler months.
PESTS & DISEASES
In Florida, scale and mealybug will occasionally attack these plants. We have found that Cygon-2E, Isotox, Malathion, and Orthene give good control. We do not use Cygon more frequently than once every 120 days however, and generally try to rotate the insecticide. After spraying, wash off all buds and flowers with plain water to prevent damage, - the same applies to your person (and of course, avoid inhalation of the fumes). Fungal and bacterial infections can be a problem because of the desired high humidity conditions. Good air movement is a big help in prevention. Some preventive fungicides are - Captan, Truban, Tersan, Physan, and Kocide, while remedial fungicides such as Subdue and Aliette are available in the USA.