The objectives of good orchid culture are to promote 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 Vandaceous orchids which we will discuss fall mainly into the genera of Vanda. Ascocentrum and Ascocenda (Vanda X Ascocentrum). For the purpose of culture, we may continue to treat Euanthe sanderiana, the reclassified species from which most of our popular vandaceous hybrids originated, in the genus Vanda.
When considering the cultural requirements of vandaceous plants, it is important to remember that all vandaceous orchids are of monopodial growth habit. This type grows from the tip, or crown, of the plant. Lateral buds are present on the main stem and these may develop into plantlets when the plant has attained sufficient size and strength to support them. In accordance with the growth habit of the main stem, each plantlet will also continue to grow indefinitely from its tip. The inflorescences of vandaceous monopodial orchids emanate from the azils of the leaves which are arranged in two rows or ranks. The stem spaces between leaves are extremely variable in size, from less than an inch to several inches apart.
Strap-leaved plants have flat, 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 which are circular in transverse cross-section. The most common species in this group are V. teres and V. hookeriana.
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.
Cultural requirements can be generally summarized in the five categories of temperature, water or humidity, light, air movement, and fertilizer. We will consider each category individually as it applies to vandaceous orchids:
Temperature
Vandaceous orchids grow best under daytime conditions of 65° or higher (30°C or higher), but 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 temperature and bright light. Night temperatures should not generally be lower than 55°F (12°C). We have seen some vandaceous plants withstand temperatures as low as 38°F (4°C) for 2-3 hours with damage to root tips and flower buds, but not to the plant itself. It is most important to protect plants from air movement during brief periods of extreme cold.
Light
The strap-leaved types can be grown indoors, in greenhouse conditions. With high humidity, maximum sunlight should be given with only enough shade to keep the temperature within the appropriate range. For our greenhouses in South Florida we use 46% shade cloth covered with 6 mil plastic on the top and sides of greenhouses, producing about 50% shade.
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 landscape use.
Air Movement
In the greenhouse, under summer sun, vigorous air movement from a fan is important to keep leaf temperature down and avoid cell damage from heat. As mentioned previously, it is important to restrict air movement under colder temperatures.
Water
A high daytime humidity is essential, especially on sunny days, and misting once or twice a day in bright weather will be helpful. On hot, sunny days around 80% humidity is appropriate. Water 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 of vandaceous orchids also requires some help from man-made supplies: containers, potting media, insecticides, fungicides, and fertilizers.
Fertilizing
Vandaceous orchids are heavy feeders. Once a week during the growing season, plants should be given a solution of a complete fertilizer. High-nitrogen fertilizers should not be used on vandaceous plants as they will inhibit flowering. All plants should be flushed thoroughly with plain water once a week to remove built-up salts. If using an automatic proportioner, plants may be fertilized as often as daily with a more dilate solution. Whatever feeding plan you follow, remember it is important to be faithful to the regimen you have established.
At our nursery we use Peter's® 20-20-20 (All Purpose)® fertilizer weekly during the growing season. Inside the greenhouse, under a controlled environment, the concentration we use is the standard recommended one of 1 teaspoon per gallon. During the winter, i.e. non-growing season, we apply the same proportions every two weeks rather than weekly. In addition, at every third feeding we substitute Peter's® 10-30-20 (Bloom Booster)®. This substitution applies to plants in all seasons of the year. Further, once a month we add 1/4 teaspoon of SUPERthrive®, a concentrated vitamin and hormone solution for plants, to each gallon of fertilizer solution.
Potting
Vandaceous plants will grow very well in any porous medium if properly aerated. Tree-fern chunks, coarse bark or charcoal are good choices. The roots should not be smothered by tight potting or soggy medium. Wooden baskets are preferred, but pots can be used if drainage is good. If potting in baskets, those made of teakwood are the best choice as they will last the longest. If teakwood is not available, redwood is a good second choice, and cedar a third option. We use 3" teakwood 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 maintaned under slightly more shaded conditions until they are established.
Because vandaceous plants have large aerial roots, they do not like to be disturbed by removal from their container. Therefore, we "elevate" plants from smaller to large baskets. This step-up procedure is accomplished by soaking the roots briefly in water until they become plible. Roots are then worked through the slats in the larger basket as the old smaller basket and plant are placed 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, or 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 gtrowth of new roots.
There are occasions, however, when distubing the roots cannot be avoided, e.g. a rotten basket, or repotting of plants grown in pots. These plants should be soaked in water, removed as carefully as possible, and placed in a solution of vitamins/hormones and fungicide, allowed to soak 5 minutes and then potted in a new basket.
The best season for the potting or repotting of vandaceous plants is late spring to early summer, but these orchids may be repotted at almost anytime of the year.
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