How We Grow Dendrobiums, Part 3
In this “chapter” on growing dendrobiums, we’ll cover the plants in two closely-related sections: Phalaenanthe and Spatulata, commonly known as the “phalaenopsis type” and “antelope type”. The species interbreed readily and most of the popular dendrobium hybrids, sometimes called “den-phals”, are descended from these two groups. The “phalaenopsis” or “den-phal” type gets its name from the flowers’ resemblance to Phalaenopsis orchids; the plants produce arching sprays of flat, white or pink to red-purple flowers.
The “antelopes” typically have twisted sepals and upright, twisted petals that suggest an antelope’s horns, and have a wider color range. Some hybrids between the two groups, especially those with a lot of “antelope” ancestry, are called “semi-phal”, as the flower characteristics are intermediate between the two.
These orchids are native to northern Australia, parts of New Guinea and Irian Jaya, where they inhabit two different climate areas. The species native to Australia generally experience a very seasonal climate, with distinct wet and dry periods during the year; the New Guinea species hail from areas where there is moderate to heavy rainfall throughout the year, with little if any dry season. Understanding this difference is important to success with these dendrobiums, particularly as the most popular “den-phal” hybrids have the most seasonal species in their ancestry.
Except for the seasonal rainfall pattern in their habitats, other growing conditions are similar. These are generally upright plants, with leafy, tall, cylindrical pseudobulbs or “canes” that can grow to quite large size in some of the New Guinea species. Den. canaliculatum and Den. affine, from Australia, are typically compact growers and their relatively small size is often used to reduce the plant size in hybrids, but some of their cousins can produce canes 6 or more feet tall. Even the common “den-phals” one sees in nurseries and garden centers are often two or three feet tall; a well-grown plant of Den. violaceoflavens can reach 7 feet or more in height, without the long stem of flowers. Not many “windowsill” orchids among the species in these sections!
Temperature. All of the species in these two groups, and consequently their hybrids, are very warm-growing. Only Den. crispilinguum will grow under “intermediate” conditions, with night temperatures below about 60F; it grows at higher elevations in New Guinea, and is not common in cultivation. The rest require warm to even hot daytime temperatures, and warm (above 60F) nights, year-round. Exposure to cooler temperatures can result in rapid leaf-drop, so these dendrobiums need to be protected in cool weather. Even here in South Florida, our winter nights can be too cool for these orchids to remain outdoors.
Light. These are generally high-light orchids. Some of the species grow in full sun, and all want as much light as possible without burning the leaves. Most will do well under “vanda” light conditions.
Water. As indicated earlier, these orchids fall into two groups with respect to watering. The Australian species are native to areas with a distinct dry season. This group includes Den. bigibbum, Den. phalaenopsis, Den. affine (syn. dicuphum), Den. canaliculatum and Den. undulatum (syn. discolor). During the summer and early fall growing season, water generously and regularly, but gradually reduce water in the fall and keep the plants on the dry side through the winter and early spring. Humidity is fairly high during the dry season, so the plants do need a little water, but allow them to dry thoroughly between occasional light waterings. Most of the common “den-phal” hybrids are in this group.
The second group, which includes the New Guinea “antelopes”, come from habitats where rainfall is moderate to heavy all year, with only a slight reduction (if any) in moisture for a short period in late summer or early fall. These plants do not want a dry rest. Water regularly throughout the year, and make sure the potting medium drains well. Good air circulation is important. Species in this group include Den. antennatum, Den. gouldii, Den. lasianthera, Den. lineale, Den. mirbelianum, Den. stratiotes, Den. strebloceras, Den. sylvanum, Den. tangerinum and Den. violaceoflavens. Hybrids with mostly “antelope” ancestry require these same conditions.
In all cases, be careful with water when the new growths begin, and keep water out of the tops of the new growths until they are two or three inches tall. The new growth is highly susceptible to rot if water is allowed to collect in the tip.
Fertilizer. These dendrobiums benefit from regular feeding when they’re actively growing. Any balanced, water-soluble fertilizer can be used, diluted according to package directions. Jack’s Classic 20-20-20 is a good option; we feed once a week during the growing season. For the dry-season plants, reduce feeding in the fall and eliminate it completely when the plants are resting in the winter. Resume feeding when the plant begins to grow again.
Potting. Given the size of most of these orchids, pots are the best solution, and heavy clay pots are a necessity. Like many other dendrobiums, these have fine root systems and do best when somewhat underpotted, with their roots crowded in a container that seems too small for the size of the plant. To add weight to an obviously top-heavy plant, set the pot into a larger size and fill the space between pots with clean river gravel for weight. The potting medium must be open, well-aerated and very free-draining; we prefer coarse expanded clay and/or coarse charcoal. Some successful growers use charcoal exclusively. Until the plant is well-established in its container, you may have to stake the tall canes to keep everything upright.
Problems. These dendrobiums have few really major pest problems. Snails and slugs may damage the leaves and canes, and occasionally during wet weather you may see some minor damage from leaf-spotting fungal diseases. In dry weather, mites can set up housekeeping on the underside of the leaves. Stale or decayed potting medium can lead to root problems, as with any potted orchids.
Reminder: all the orchids in these sections are very warm-growing. The plants must never be exposed to cool temperatures.
With good care, these orchids are capable of blooming multiple times from the same canes!
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