How We Grow Dendrobiums, Part 1
Dendrobiums are native to a huge area in Asia, ranging from southern Japan and the eastern foothills of the Himalaya south into India, the Indo-China peninsula, Malaysia, Indonesia, New Guinea and Australia. In this large range, there are at least 1,000 species, inhabiting virtually every tropical and subtropical habitat, so it is impossible to generalize about their cultural requirements. Some live in areas that are warm all year long, some grow in cool cloud-forests. Some thrive in conditions that are generally moist all or most of the year, some are adapted to sharply seasonal wet/dry cycles. We grow many dendrobiums from the warm to intermediate temperature habitats, and we’ll share our experience with some of these extraordinarily beautiful orchids.
Botanists place groups of related species into “sections”, to help organize and identify plants. Here in “part 1”, we’ll discuss some of the related species from Section Dendrobium. These are sometimes referred to as the pendent, and/or deciduous dendrobiums, as most of them produce pendent stems (or “canes”) that are often leafless during their dry-season resting period. There are estimated to be 50 to 60 species in this group. Of those, we grow about a dozen species: Den. anosmum (superbum), Den. aphyllum (pierardii), Den. parishii, Den. nobile, Den. signatum, Den. albosanguineum, Den. moschatum, Den. fimbriatum, Den. primulinum, Den. pulchellum, Den. senile, Den. unicum.
Most of these species are native to northeastern India, and parts of the Indo-Chinese peninsula, although one species, Den. anosmum (also known as Den. superbum) is common from the Philippines through Malaysia and Indonesia. This group of dendrobiums is popular for the spectacular, fragrant show of flowers in the springtime.
Fortunately, the most popular species in the group all have similar cultural requirements. They grow robustly during spring and summer; growth stops altogether in late fall, and the plants may drop their leaves during the winter resting period.
Temperature. In their native habitat, these orchids experience mild to warm daytime temperatures in spring and summer, and generally cooler temperatures in the winter. For most, the winter night temperatures range from about 45°F to about 55°F. Den. superbum, particularly the plants from the Philippines, prefers winter nights about 10 degrees warmer than that. These plants do well for us with our normal winter night temperatures, which are usually in that range.
Light. While actively growing, give the plants plenty of bright but filtered light. They will grow well under the same light conditions as most cattleyas. Most of these dendrobiums grow attached to deciduous trees, so they want higher light in winter. We grow them under cattleya light levels during the growing season, and move them to vanda light levels during their resting period.
Water.This may be the most crucial element to success with these orchids. Their native conditions are fairly wet during the late spring, summer and early fall. Rainfall is quite heavy for a few months, but it tapers off in the late fall, and winter months are fairly dry. Water the plants regularly when they are actively growing. Mounted plants can be watered daily if air circulation is good.
Observe the tips of the canes; in the fall, they will stop producing new leaves. This is the signal that the plant has finished growing for the season; gradually reduce watering, and allow the plant to dry somewhat between waterings. There’s some moisture in the habitat at this time, so the plants do get a little water from dew or fog; a light watering every few days is all they need. Growth will start again in the late winter or early spring at about the same time that the flower buds begin to form; once the buds have formed, and new growth appears, increase watering again.
Remember, it’s quite typical for these dendrobiums to drop all or most of their leaves during their winter resting period. Flower buds will appear on the stem opposite the attachment points of the leaves, and new growth will commence from the base of the previous year’s growth.
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. Reduce feeding in the fall and eliminate it completely when the plants are resting in the winter. Resume feeding after the flowers have finished.
Potting. The pendent stems of these orchids make them a challenge to grow in pots, so they are usually grown mounted, or in hanging baskets. The larger species can grow to great size, so if mounted, the mount material should be sturdy – a cork slab or dense tree fern plaque works well. Mounted plants can be watered daily in summer if the air circulation is good. In a basket, use a very well-drained epiphyte mix. We prefer to mount these dendrobiums.
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.
If, in the spring, the plants produce keikis (baby plants) on the stem instead of flowers, the plant is telling you that something in its environment is not correct. This may be too much water during resting; the plants need a little watering during this time but they must dry completely for two or three days between waterings. It may also be a temperature problem…these dendrobiums want mild to warm days in winter, but much cooler nights. And they need higher light in the winter, too.
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