The Ascocentrum genus is a relatively small group of about 10 species that hails from the Asian tropics—yet from a collector's point of view, these are extremely important plants. Ascocentrum plants are closely related to Vandas and easily hybridize with these orchids. The resulting Ascocentrum x Vanda cross is known as Ascocenda, or Ascda. The Ascocenda plants offer the very best of both their parents: they are compact monopodial plants that can easily be grown indoors; they have the same outrageously awesome growth habit; and they boast the jewel-like flowers of the Vandas. If you have any interest in growing hanging monopodial orchids, my advice is to start with an Ascocenda. Once you've mastered these plants, you can move up to the much larger Vanda plants.
Taxonomy and Structure
Ascocentrum are in the Vandeae tribe and Sarcanthinae subtribe of orchids. They are closely related to Vandas and Renantheras and easily hybridize with these plants. Ascocentrum are monopodial orchids, like Phalaenopsis, meaning they lack pseudobulbs and grow from a single stem, with their roots emerging from the bottom of the growing stem.
Ascocentrum have strap-like leaves that emerge alternating left and right. Their roots emerge from the bottom of the stem, but sometimes roots will emerge from between leaves and wander into the open air. Over time, older plants will branch and gradually increase the plant's overall size. Propagation by division is possible by removing side stems, providing they have at least two healthy roots established.
Like Vandas, Ascocentrum thrive in strong, bright light. They can be acclimated to direct sunlight, and in areas where they are grown outside, can sometimes be seen in nearly full morning sunlight. Plants that are receiving enough light have light green leaves with red mottling on the leaves. Leaves that are dark green or a lack of flowering typically indicate inadequate light. In northern latitudes, the winter is particularly challenging when it comes to light. Growers in these areas might need to supplement with an HID light. In the summer, your Ascocentrum might appreciate being hung in a tree outside.
As with all orchids, the amount and frequency of watering depend on the growing habit. Ascocentrum orchids can be grown in pots, in a very fast-draining orchid mixture, or they are particularly well suited to basket culture. Many growers who have greenhouses grow Vandaceous orchids in open slatted baskets with no growing medium and the roots hanging free in the open air. In general, Ascocentrum have fairly high water requirements. Hanging plants should be watered or misted daily. To correctly water a hanging Ascocentrum, give it a good soaking, then let it dry for two or three minutes and water it again. The roots should turn green or silvery as the plant absorbs water.
Providing adequate humidity is also important: A minimum of 60 percent is necessary for healthy growth, but more is better. There is no upper tolerance—these orchids are well suited to 90 percent humidity, providing there is a strong airflow. A healthy plant should remain cloaked with leaves all the way to the bottom of the stem. If the plant starts dropping leaves, the most likely culprit is lack of water or improper feeding.
Ascocentrum is a heavy feeder. Fertilize weekly with a 1/2 strength orchid fertilizer. Plants that are properly fertilized will retain their leaves and bloom much more vigorously.
Ascocentrum is warm-house orchid that prefers temperatures above about 65 F. They can tolerate lower temperatures, but a prolonged exposure to colder temperatures will have a profound effect on the plant's growth and flowering. Exposure to any temperatures below 50 F can cause delayed flowering for up to a year.
The plants typically flower in the late winter or early spring, although my Ascocenda hybrids have been known to throw flower spikes throughout the year. The plants flower from an upright inflorescence that is covered with small, perfectly shaped flowers. Ascocendas follow this same pattern: an upright inflorescence that looks like a cone of flowers. True Ascocentrum flowers are often red, scarlet or deep orange, depending on the species.
Potting and Media
Ascocentrum and the closely related Asocendas really do best as mounted plants. Most growers prefer growing them in open slatted baskets, wiring the plants into place until the roots have had a chance to work their way through the basket and firmly hold the plant in place. As they plants grow, they sometimes need additional support to prevent tipping over; this can be provided by wiring the main stem loosely to the basket support. Plants grown in this way will eventually develop a hanging curtain of white roots. People who are unfamiliar with orchids are always enchanted by the sight of a beautiful orchid seemingly growing in mid-air (not knowing, of course, that you water it daily!). Baskets can be made from cedar or plastic. You can also grow these plants in containers, but it is absolutely essential that you use a very fast draining mix and allow the plants to completely dry between watering. Despite their extremely high water requirements, dampness is the enemy of these beautiful plants.
The roots must be allowed to completely dry out.
Ascocentrum and indeed all Vandaceous orchids are not really beginner's plant. They require more maintenance than your average Phalaenopsis, including sometimes daily watering and rather more extreme growing conditions (high humidity, high temperatures, very bright light). Additionally, growing them well requires some patience in the beginning—there is a natural balance between watering, humidity, temperature, air flow, and light that is optimal. It's hard to say exactly what this is because every growing situation differs a little bit. To some degree, it's just a matter of feeling it out, learning to recognize this sweet spot by instinct as much as anything else. But don't let me discourage you: there's a reason these plants win so many awards, a reason that people literally build additions onto their homes to keep Vandaceous orchids. They are exotic and beautiful and temperamental, and they reward your efforts with sublime displays of blooms.