Dendrobium

Dendrobium is a large genus of about 1600 tropical and subtropical herbaceous perennials in the orchid family (Orchidaceae). They are native across a wide area from India, China and Japan to Australia, New Zealand and New Caledonia. The genus name comes from the Greek words dendron, meaning a tree, and bios, meaning life.

The enormous diversity of this genus defies one-size-fits-all growing instructions. Many of the species in this genus have active growing periods alternating with periods of rest. Overwatering when the plant is dormant, or underwatering when the plant is growing can have fatal results. Dendrobiums grow best in bright, indirect light, ideally in a west or south-facing window. A partially shaded site providing 2,000 to 5,000 fc light intensity should be sufficient (full, direct sunlight is approximately 10,000 fc by comparison). They prefer high humidity, around 60% or more but with good air circulation. The potting medium – a special orchid mix based on tree bark is best – should dry out partially between waterings but never be fully dry (unless the plant is completely dormant). The genus includes deciduous species that lose their leaves during the dry season in nature. For these species, withhold water in the late fall and early winter to mimic natural conditions and stimulate blooming. Because these plants have small root systems, they should be planted in the smallest pot that fits. Clay pots work well for maintaining good potting medium aeration and drainage, and they prevent plants from becoming top-heavy. The genus also includes hot-, intermediate- and cool-growing species, so consider temperature requirements to optimize growth and flowering. Feed weekly during the growing season. Use a specialist orchid fertilizer diluted in water according to the label directions. 

The most commonly cultivated members of the genus can be divided informally into two groups: the hard-cane types and the soft-cane types. The hard-cane dendrobiums are mostly evergreen and produce leafy, erect, cane-like pseudobulbs. The inflorescences emerge as racemes from the upper nodes of the pseudobulb. The widely available Dendrobium bigibbum var. superbum (syn Dendrobium phalaenopsis) and its hundreds of hybrids are hard-cane types, as are the antelope dendrobiums (D. antennatum and hybrids). The soft-cane types have erect or pendent, thin, cane-like pseudobulbs that are mostly deciduous. Their flowers emerge singly or in small clusters from the nodes along the length of the cane. The popular D. nobile and its many hybrids, as well as D. aphylla and D. anosmum belong to this group. Other species and hybrids, not belonging to either of these groups, are sometimes grown by orchid enthusiasts.

The flowers come in a wide range of colors and shapes. Some are fragrant. The flowers of the hard-cane types are long-lasting, while those of the soft-cane types have a shorter lifespan. The hard-cane types make easy-to-grow houseplants that can spend their summers outdoors.

Quick ID hints:

• Narrow, elongated pseudobulbs that are segmented (cane-like)
• Racemes of flowers without a sheath or flowers borne in small clusters the length of the canes.
• A nectar spurs at the back of the flower

Diseases, Insect Pests, and Other Plant Problems: These plants have few problems. They are generally not affected by pests but watch for mealybugs. Insufficient light results in non-blooming.

VIDEO Created by Laura Barth for "Houseplants, Succulents, and Cacti", a plant identification course offered in partnership with Longwood Gardens.