Habitat and Ecology
​Oncidium hallii (often cited under its older name, Odontoglossum hallii) is a medium-sized, epiphytic or terrestrial orchid native to the Andes of Colombia and Ecuador. It is a cold-to-cool growing species, found in very wet montane cloud forests at high elevations, typically ranging from 1,200 to 3,000 metres. This demanding habitat is characterized by constant moisture from fog and mist, cool temperatures year-round, and intense, filtered light when the clouds break. It grows on small trees or terrestrially in thick leaf litter.
​Description
​Commonly known as Hall's Odontoglossum, this orchid forms dense clumps of clustered, compressed pseudobulbs, each bearing one or two apical, leathery leaves. The spectacular flowers are borne on a long, erect to arching spike (up to 60 cm long) that can be simple or branched, carrying several to many blooms. The individual flowers are large (up to 10 cm wide) and highly intricate. They are typically yellow or greenish-yellow, heavily and irregularly spotted or blotched with large markings of purplish-brown or dark red across the sepals and petals. The prominent lip is white with bright yellow markings on the crest (callus) and often has a jagged or toothed margin. The flowers are fragrant and usually appear in spring and summer.
​Cultivation
​Oncidium hallii is a challenging cool-growing orchid that is best suited for a cool greenhouse or specialised orchidarium in the UK where its cool-night requirement can be consistently met. It needs bright, filtered light; high light is essential for flowering, but direct sun should be avoided. Use an open, very well-draining medium of coarse bark, charcoal, and perlite. The medium must be kept evenly moist year-round; it should not be allowed to dry out completely at the roots.
​Optimal Daytime Temperature: 15-23 C (59-7 F)
​Optimal Nighttime Temperature: Cool nig&*F).
​High humidity (60-80%+) and excellent air circulation are mandatory to prevent fungal issues on its large leaves. Water frequently with tepid, soft water (rainwater is preferred). Feed monthly during the growing season with a balanced, dilute liquid orchid feed.
​Unique Features
​This orchid is a highly prized collector's item for its magnificent flower size and dramatic, leopard-like spotting on a yellow background. The combination of its intricate crest (callus) on the lip and its requirement for high-altitude, cool growing conditions make it a rewarding but difficult species to flower successfully. Its inclusion in the Odontoglossum group highlights its elegance and unique floral complexity.
​Specifications
​Plant Size: see exampl  pictite above.
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​Plant Family: Orchidaceae
​Plant Passport: A Oncidium hallii B 140084 C [user input] D GB