The objective of good orchid culture is robust, disease-free plants with high quality blooms. These goals are especially important for vandaceous orchids, which produce quality flowers only from strong plants.
The most common vandaceous orchids are Vandas (including recently renamed Ascocentrum), and Ascocendas. Here in South Florida we also grow many other species and intergeneric hybrids such as Rhynchostylis, Aerides, Aeridovanda (Aerides × Vanda), and numerous other combinations of these closely-related plants.
It’s important to remember that all vandaceous orchids are monopodials. Monopodial orchids have a single stem and growing point at the tip, or crown, of the plant. They are generally upright in habit, and the main stem may have lateral buds which can develop into plantlets (“keikis”) when the plant has attained sufficient size and strength to support them. Each keiki will also continue to grow indefinitely from its tip.
Vandaceous orchids have leaves arranged in two rows or ranks along the main stem, and the inflorescences emerge from the leaf axils (the angle where a leaf is attached to the main stem). Spacing between leaves is extremely variable, from less than an inch to several inches apart depending on the plant’s breeding.
There are three broad types of leaf shape among Vandaceous orchids: strap-leaf, terete and semi-terete, and the three groups have somewhat different cultural needs. (Note that there are also terete-leaf orchids unrelated to vandas.)
Strap-leaf plants have flat or V-shaped, leathery leaves. This category includes such vanda species as coerulea, dearei, luzonica, merrillii, tricolor and sanderiana, as well as the ascocentrums.
Terete orchids have tapering, pencil-shaped leaves that are circular in cross- section. The most common vandaceous species in this group are Papilionanthe teres and Ple. hookeriana. Sometimes these are called terete vandas.
Semi-teretes, as they are referred to here, are a hybrid combination with some terete species in the background.
Their leaves are somewhat pencil-shaped and tapered but not always completely round in cross-section. In some hybrids the leaves are rigid and attach to the stem at a sharp angle.
Success with vandaceous orchids requires attention to five elements of their growing conditions:
Temperature. Vandaceous orchids grow best under daytime conditions of 65ºF (18ºC) or higher, but they can withstand long spells of hot weather and short spells of cold. They will continue in active growth anytime of the year if given warm temperatures and bright light.
Night temperatures should not generally be lower than 55ºF (12ºC) for extended periods. We’ve seen some vandaceous plants withstand temperatures as low as 38ºF (4ºC) for 23 hours with damage to root tips and flower buds, but not to the plant itself, but you should protect your vandaceous orchids from those temperatures if at all possible. During a period of extreme cold, the most important thing you can do is to protect the plants from air movement (wind). For the most part, vandaceous orchids fall into the “warm-growing” group mentioned in most books and publications about growing orchids.
Light. If the humidity is high, maximum sunlight should be given with only enough shade to keep the temperature within the appropriate range and protect the foliage of strap-leaf plants during the middle part of the day. For our greenhouses in South Florida we use 46% shade cloth covered with 6 mil clear plastic on the top and sides of greenhouses, producing about 50% shade. Outdoors, the plants want maximum light without burning the leaves. They will benefit from full sun in the morning and late afternoon, but need some shade during the middle part of the day.
Terete vandas and their semi-terete hybrids are sun lovers. Not only will they flower year round in tropical areas, they are also floriferous in the subtropics. They can be grown in the full sun and are ideal for tropical landscape use.
Air Movement. Vandaceous orchids are epiphytes and need good air circulation. Air movement also reduces the incidence of leaf-spotting fungal and bacterial infestations. However, as noted above it is important to restrict air movement under colder temperatures.
Water. Vandaceous orchids in slat baskets should be watered daily, preferably early in the morning. Give them a good drink with the hose, or a dunk in a bucket or sink if you only have a few plants, and let them dry. High daytime humidity is essential, especially on sunny days, and additional misting once or twice a day in bright weather will be helpful. On hot, sunny days around 80% humidity is appropriate. Water more sparingly in winter, during long cloudy spells, or after repotting. In any season, avoid watering plants late in the afternoon. Vandaceous plants should be dry before nightfall.
In addition to the natural ingredients of temperature, air and water, good culture also requires some help from manmade supplies: containers, potting media, insecticides, fungicides, and fertilizers.
Fertilizing. Vandaceous orchids are heavy feeders. Once a week during the growing season, give the plants a solution of a complete, balanced fertilizer. High-nitrogen fertilizers will inhibit flowering and are not recommended for these orchids. All plants should be flushed thoroughly with plain water once a week to remove built-up salts. If you use an automatic proportioner, plants may be fertilized as often as daily with a more dilute solution. Whatever feeding plan you follow, remember, it is important to be faithful to the regimen you have established.
We use Peter’s 20-20-20 (All Purpose with micronutrients; Jack’s Classic All-Purpose is packaged for consumer sales) fertilizer weekly during the growing season. Inside the greenhouse, under a controlled environment, we use the standard, recommended concentration of 1 teaspoon per gallon. During the winter (non-growing season), we apply the same proportions every two weeks rather than weekly. In addition, at every third feeding we substitute Peter’s (or Jack’s Classic) 10-30-20 (Bloom Booster). This substitution applies to plants in all seasons of the year. And once a month we add 1/4 teaspoon of SUPERthrive, a concentrated vitamin and hormone solution for plants, to each gallon of fertilizer solution. SUPERthrive is a root stimulant, not a fertilizer.
Potting. Vandaceous plants will grow well in any porous medium if properly aerated. Tree-fern chunks, coarse bark or charcoal are good choices. The base of the plant and roots should not be smothered by tight potting or soggy medium. We prefer wooden or plastic baskets with little or no additional growing medium, but pots can be used if drainage is good. Teakwood is the best choice for wood baskets, as it lasts the longest. If teakwood is not available redwood is a good second choice, and cedar a third option.
We use 3″ teakwood or plastic baskets for the first two years after seedling size, 6″ baskets for the next two years, and 8″ baskets for mature plants. Plants should be suspended so that the aerial roots are free; otherwise, the roots attach themselves to the bench or wall and are damaged when the plants are moved. Recently potted plants should be maintained under slightly more shaded conditions until they are established.
Because vandaceous plants have large aerial roots, they don’t like to be disturbed. So instead of removing them from their smaller, older baskets at repotting time, we “elevate” plants from smaller to larger baskets. We soak the roots briefly in water until they become pliable, and then work the roots through the slats in the larger basket so that we can place the old smaller basket and plant intact in the larger basket. Never coil the roots around the old basket because vandaceous plants will feed better with an unrestricted root system.
A few large pieces of charcoal can be added to hold the smaller basket securely within the larger; wiring the smaller basket into the larger will accomplish the same result. This method minimizes shock to the plant and permits continued, uninterrupted growth. Adding SUPERthrive to the water used to soak the plant will further minimize its shock and seems to encourage faster growth of new roots.
There are occasions, however, when disturbing the roots cannot be avoided, e.g. a rotten basket, or repotting of pot-grown plants. Soak these plants in plain water for a few minutes, and then remove from the old container as carefully as possible. It may be necessary to dismantle the old basket by cutting its wire fasteners. Clean debris from the roots and soak in a solution of vitamins/hormones and fungicide for about 5 minutes, and then pot in a new basket. If you must trim roots or leaves, be sure your cutting tool is sterilized.
Late spring to early summer is the best season for potting or repotting vandaceous plants, but these orchids may be repotted at almost anytime of the year.
Since vandaceous orchids grow rapidly with good light, water and regular fertilizing, seedlings should be grown in 3″ pots, loosely potted in a mix of fine charcoal and tree-fern fiber. Keep seedlings in slightly more shaded conditions than mature plants, but include them in the same water and fertilizer programs. Maintain humidity and good air movement.
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