How We Grow Dendrobiums, Part 4
Another group of Dendrobiums, section Pedilonum, includes about 80 species from a wide swath of Asia, from India across southeast Asia to the Philippines and south to New Guinea. Many of the species in this section are cloud forest plants which require cooler conditions than we have in South Florida, but some of the most beautiful and interesting species are warm to warm-intermediate growers, and we do cultivate those here at R.F. Orchids.
These orchids grow at sea level, or at low elevations, where the temperature is warm to hot all year long, and with two exceptions (noted below), the plants do not experience any significant dry season. We’ll cover Den. bullenianum (syn. topaziacum), Den. capituliflorum, Den. goldschmidtianum (syn. miyakei), Den. purpureum, Den. secundum and Den. smillieae. In this group, the individual flowers are small but the plants produce clusters of them all at once, making a spectacular display. Den. secundum and Den. smillieae are usually spring bloomers; the other species can bloom at nearly any time of the year.
For the most part, the warm-growing species in section Pedilonum are medium sized to large epiphytes, with slim, leafy canes (stems) that become pendent as they grow. Typically these canes are deciduous after about a year, and the plants bloom from nodes along the bare stems. Den. purpureum is the largest of the species in this group, with canes that can grow to three or four feet long; the plants strongly resemble Den. anosmum (superbum) but have different cultural requirements. There are several color forms of Den. purpureum; the most commonly cultivated forms are pink, and white with green tips.
Temperature. These dendrobium species 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 plants must be protected in cool weather. Even here in South Florida, our winter nights can be too cool for these orchids to remain outdoors on cold nights.
Light. Grow these dendrobiums in bright shade, about the same light levels you have for your cattleyas. Den. smillieae will take somewhat brighter light during the winter months.
Water. In general, the species in this group come from habitats where there is year-round moisture. Most don’t need a dry resting period in the winter, although both Den. secundum and Den. smillieae should be watered less during the winter. Never allow the plants to remain dry for an extended period, however; in their native habitats rainfall is only slightly less in winter and early spring than in the rest of the year. Good air circulation is important, and the plants should be watered regularly but not be constantly wet.
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 (spring through fall). If the plants are growing – making new leaves at the tips of the canes, or new growths from the base of the mature canes – fertilize regularly. During the shorter, cooler days in winter, feed less often.
Potting. These dendrobiums can be grown in pots, baskets or on mounts. Because most of them are medium to large plants with eventually pendent stems, many growers prefer to mount the plants on a sturdy substrate; cork, treefern, teak root or driftwood work well. It’s also possible to encourage upright growth by staking the new canes as they grow; left to themselves the canes will eventually become horizontal or pendent. Den. capituliflorum has shorter, thicker pseudobulbs that generally don’t require staking. The short form of Den. smillieae grows more upright than the large form. Plants in pots or baskets need an open, fast-draining medium.
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 noted in this chapter are very warm-growing. The plants must never be exposed to cool temperatures. (There are other species in Section Pedilonum which are cool or cool-intermediate growers; we don’t grow or sell those plants)
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