Vanda Alliance The Vanda Alliance, as this varied group of plants is called, is made up mostly of warmth- and sun-loving orchids with very colorful flowers. Originating from tropical Asia, they are easily grown in warm climates, where plants are grown outside in light shade, such as in a lath house. In climates where winters are cold, they are often summered outside, an grown inside during the winter in a sunny window, or year-round in a greenhouse. LIGHT is a crucial factor in blooming some vandaceous plants. There are three types of vandas: strap-leaf, semiterete and terete. The first type has broader, flat leaves, while terete types have round, pencil-shaped leaves. The semi-teretes are hybrids between the two, with an intermediate shape. Terete types need full sun, and are best grown in high light climates. In warm, bright climates, you can grow any type of vanda, outside (if warm) with partial shade for strap-leaf types and semiteretes (especially in midday in summer) or inside (when cold) in a bright, south window. In climates where winters are dull, try strap-leaf types (or ascocendas); grow them outside in summer an in full sun inside during the winter. In a greenhouse, give the plants about 25% to 35% shade, less in winter if dull. Leaves should be a medium green, not dark green. TEMPERATURE for most vandas should be warm; a minimum winter night temperature of 55 degrees F is recommended. Colder spells can be tolerated for a short time if it is not windy. Optimum temperatures are 60 degrees F at night, and a maximum of 95 degrees F during the day. Warmer temperatures mean faster growth, which must be balanced with higher humidity, air movement, and increased water and fertilizer. Days should be warm and humid for optimum plant growth. WATER. Vandas generally like lots of water when growing, but must dry quickly. Because of this, and their extensive root system, they are mostly grown in slatted wood baskets, or in pots with a coarse potting medium. If warm and sunny, they may need daily watering, with misting several times a day in dry or hot climates. Water sparingly in the winter or during cloudy weather, but do not allow plants to shrivel. HUMIDITY of 80% is ideal. In tropical climates this may be easy to obtain. Yet in most climates, misting may be necessary during sunny weather. In a greenhouse, this is easier to provide by wetting down the floor, or using an evaporative cooler. In the home, place the plants on trays of gravel, partially filled with water. Do not mist the plants if the leaves will not dry by nighttime. Air movement must be strong. FERTILIZING. A well-balanced (20-20-20) fertilizer applied full strength once a week is recommended when warm, or use 1/4 strength every watering. During cool or cloudy weather, apply fertilizer once every two to four weeks. Use a high-phosphorus fertilizer (such as 10-30-20) ever third application to promote blooming. A vitamin B1 compound may be beneficial; use it once a month. POTTING should be done in the spring. Plants in baskets do not need to be repotted often; leave them unless the potting medium breaks down. Just set the plant, with the old basket, into a container of water to make the aerial roots more pliable, and then set plant and basket into a larger basket. For plants in pots, repot in a slightly larger pot, positioning the plant in the center. Use a coarse medium, whether fir bark, treefern, charcoal, etc., and work it around the roots. Keep shaded, humid, but drier at the roots until new root tips grow. Do not overpot. Prepared by: Education Committee, American Orchid Society 6000 S. Olive Ave., West Palm Beach, FL 33405 (407) 585-8666.