The Dendrobium anosmum orchid, sometimes called the Unscented Dendrobium despite its fragrant blooms, offers a rewarding cultivation experience. This large epiphytic orchid features long, arching to pendulous canes, reaching up to 10 feet (300 cm) in its natural habitat. Its fleshy, glossy green leaves are oblong-elliptic, deciduous, and typically measure 5-7 inches long. In spring, pleasantly fragrant lavender flowers, up to 4 inches across, emerge from the leafless nodes, often with two burgundy spots on the lip. Their scent can vary, evoking notes of raspberry, strawberry, rhubarb, or hyacinth.
Optimal Growing Conditions
Dendrobium anosmum thrives in bright, indirect light, mimicking its native rainforest canopy conditions. An east or west-facing window often provides suitable light indoors, or a location with 50% shade outdoors. Overly dark green leaves signal insufficient light, while yellowing or scorched leaves indicate too much direct sun.
Daytime temperatures should ideally range from 78-86°F (26-30°C), with night temperatures falling to 61-68°F (16-20°C). A consistent 15 to 20°F (8-11°C) difference between day and night temperatures benefits mature plants. Temperatures above 90°F (32°C) can be tolerated if humidity and air circulation are increased, but below 50°F (10°C) may cause leaf drop.
High humidity is important for Dendrobium anosmum, with summer levels ideally at 80-90% and winter levels around 70%. Indoors, humidity can be augmented using pebble trays (ensuring the pot does not sit directly in water) or a humidifier. Good air circulation is also important; it helps prevent fungal issues and allows the plant’s roots and medium to dry appropriately between waterings.
An epiphytic orchid compost that is loose, airy, and free-draining is suitable for potting. Common components include bark, perlite, sphagnum moss, or charcoal mixes. These orchids can be grown in pots, preferably small for their size, or mounted on tree fern washers or in hanging baskets due to their pendulous growth.
Watering and Fertilizing
During the active growing season, from late winter to summer, Dendrobium anosmum should be kept consistently moist. Water should be applied freely in summer, perhaps daily or every two days, allowing excess water to drain completely. The medium should not dry out completely during this period.
Watering frequency should be reduced in fall and significantly lessened during the winter and spring dormancy. During dormancy, water sparingly, just enough to prevent pseudobulbs from shriveling. Avoid overwatering, which can lead to root rot. When flower buds begin to swell, gradually increase watering.
Fertilize during the active growing season. From spring to mid-summer, use a high-nitrogen fertilizer weekly. Subsequently, apply a high-phosphorus fertilizer until late fall. A balanced orchid fertilizer (e.g., 20-20-20 or 10-10-10) diluted to one-quarter or half strength can be applied every one to two weeks during active growth. Stop or significantly reduce fertilization during dormancy.
Mastering the Dormancy Cycle
The dormancy period for Dendrobium anosmum encourages abundant flowering. This phase mimics the natural dry season in their native habitats, signaling the plant to initiate flower development. Without a proper rest, the orchid may produce new growths (keikis) instead of blooms.
To induce dormancy, typically starting around October or mid-November, gradually reduce watering, allowing the medium to dry out more thoroughly between applications, eventually becoming very infrequent (e.g., once a month). Cease fertilization entirely. Simultaneously, expose the plant to cooler temperatures, ideally around 60°F (15°C) at night, to trigger flower bud formation.
During dormancy, the plant’s deciduous nature becomes apparent as its leaves typically yellow and drop. This leaf loss is a normal part of the cycle, indicating the plant is concentrating energy in its pseudobulbs. Even with leaf drop, canes should not shrivel excessively; provide minimal watering if this occurs.
As late winter or early spring approaches, signs of new growth, such as swelling flower buds along the canes, will emerge, indicating the plant is preparing to break dormancy. At this point, gradually increase watering, and resume regular fertilization once flowering is complete and new vegetative growth begins.
Repotting Your Dendrobium Anosmum
Repot Dendrobium anosmum immediately after flowering, as new root growth begins in spring. This timing allows the plant to establish itself in the fresh medium before its active growing season.
Repotting is needed when the potting medium is broken down or decaying, leading to poor drainage and aeration, or when the plant has outgrown its container with no space for new growth.
When selecting a pot, choose one that provides good drainage and is only one size larger, as these orchids prefer to be somewhat pot-bound. Options include traditional pots with ample drainage holes, hanging baskets, or mounting on tree fern for their pendulous growth. The potting medium should be fresh, well-draining, and airy, such as a mix of bark, perlite, and sphagnum moss.
During repotting, gently remove the plant from its old pot and clear away the old medium from the roots. Inspect roots and trim any that are dead or mushy. Position the orchid in the new pot, ensuring new growths have sufficient space, then fill with fresh medium, potting firmly. After repotting, delay watering for a few days to allow damaged roots to heal, then resume with light watering before gradually increasing.
Troubleshooting Common Problems
A lack of blooms is a common concern, often stemming from insufficient light or an inadequate dormancy period. Ensuring the plant receives bright, indirect light and a distinct cool, dry rest in winter can encourage flowering.
Yellowing leaves might indicate overwatering, a nutrient deficiency, or natural leaf drop during dormancy. Shriveled leaves, particularly the pseudobulbs, usually point to underwatering or root rot, where roots cannot absorb water. Adjusting watering practices and inspecting roots for rot can resolve these issues.
Pests such as aphids, mealybugs, and scale can infest Dendrobium anosmum. Aphids target new growth and flower buds, while mealybugs and scale appear as small bumps or cottony masses on leaves and stems, sucking sap. Regular inspection and treatment with insecticidal soap or neem oil can manage these pests.
Fungal and bacterial diseases can affect orchids. Fungal issues like black rot or powdery mildew thrive in overly moist conditions with poor air circulation, appearing as mushy patches or white coatings. Bacterial soft spot causes brown, mushy spots with an unpleasant odor. Maintaining good air circulation, proper watering, and sterilizing tools during pruning can prevent these problems.