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ORCHID SPECIES CULTURE Charles and Margaret Baker Oncidium onustum Lindley AKA: Oncidium holochrysum Rchb. f. ORIGIN/HABITAT: Ecuador and Peru. Plants grow in the humid coastal lowlands of western Ecuador and northwestern Peru in areas where scant rainfall occurs. They are found on both cactus and trees in dry forests, usually near sea level, but collections as high 3950 ft. (0-1200 m) have been reported. CLIMATE: Station #84011, Manta, Ecuador, Lat. 1.0S, Long. 80.7W, at 20 ft. (6 m). Temperatures are calculated for an elevation of 200 ft. (60 m), resulting in probable extremes of 95F (35C) and 50F (10C). N/HEMISPHERE JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC F AVG MAX 83 84 83 83 84 84 85 85 86 86 86 84 F AVG MIN 68 67 67 67 68 69 71 71 71 71 70 69 DIURNAL RANGE 15 17 16 16 16 15 14 14 15 15 16 15 RAIN/INCHES 0.2 T T T 0.1 0.2 1.6 3.8 2.7 1.0 0.1 0.2 HUMIDITY/% 80 78 79 79 77 75 77 82 81 78 76 79 BLOOM SEASON * * * * * * * * * ** * * DAYS CLR @ 7AM 1 0 0 0 0 1 0 0 0 1 1 1 DAYS CLR @ 1PM 6 9 8 7 8 12 3 1 5 5 8 4 RAIN/MM 5 1 1 1 3 5 41 97 69 25 3 5 C AVG MAX 28.3 28.9 28.3 28.3 28.9 29.1 29.5 29.4 30.0 30.0 30.0 28.9 C AVG MIN 20.0 19.7 19.7 19.7 20.2 20.8 21.9 21.9 21.9 21.9 21.3 20.8 DIURNAL RANGE 8.3 9.2 8.6 8.6 8.7 8.3 7.6 7.5 8.1 8.1 8.7 8.1 S/HEMISPHERE JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN Cultural Recommendations: LIGHT: 2500-3500 fc. As high as the plant can tolerate, but light should be increased gradually and plants should be watched for signs of possible sunburn. Strong air movement should be provided at all times. Many species seem to flower better in bright light than in a more shaded situations. TEMPERATURES: Throughout the year, days average 83-86F (28-30C), and nights average 67-71F (20-22C), with a diurnal range of 14-17F (8-9C). Because of the relatively wide range in habitat elevation, plants should adapt to conditions 8-10F (4-6C) cooler than indicated. HUMIDITY: 75-80% year-round. In the habitat, values are near 100% in the late night and early morning hours but fall rapidly as temperatures warm after sunrise. WATER: Rainfall is very light throughout the year. Additional moisture is available from heavy deposits of dew and late-night mist. Cultivated plants will probably grow better if for most of the year they are misted every morning, but the frequency of the mistings should usually be increased somewhat in summer and decreased slightly in winter. FERTILIZER: 1/4-1/2 recommended strength, applied weekly when plants are actively growing. A high-nitrogen fertilizer is beneficial from spring to midsummer, but a fertilizer high in phosphates should be used in late summer and autumn. REST PERIOD: Growing conditions should be maintained all year. Water may be reduced especially during periods of dark, cold weather, but plants should not be allowed to remain completely dry for long periods. Fertilizer should be reduced or eliminated until new growth begins in spring. GROWING MEDIA: Plants are probably best grown and more easily managed if mounted tightly to a tree-fern or cork slab. If mounted, however, high humidity must be maintained and the plants watered at least once daily in summer. Several waterings a day may be necessary for mounted plants during extremely hot, dry weather. Plants may also be grown in pots or baskets filled with an open, fast-draining medium that allows the roots to dry rapidly after watering. Repotting or dividing should be done only when new root growth is just starting, which allows the plant to become established in the shortest possible time with the least amount of stress. MISCELLANEOUS NOTES: The bloom season shown in the climate table is based on cultivation records. In the habitat, these plants bloom from autumn to midwinter. Plant and Flower Information: PLANT SIZE AND TYPE: A small, clump-forming epiphyte 5 in. (12 cm) tall. Growths are closely spaced along a creeping rhizome. PSEUDOBULB: 1.2 in. (3 cm) tall by 0.8 in. (2 cm) across. The egg- or pear-shaped pseudobulbs, which are lightly flattened, are green with irregular brown-black markings. Each pseudobulb is protected by well-developed leaflike sheaths at the base. LEAVES: 1. The leaf, which is carried at the apex of the pseudobulb, is stiff, erect, 3.5-4.0 in. (9-10 cm) long, 0.5-0.6 in. (1.2-1.5 cm) wide, thick, leathery, sharply pointed at the tip, and folded at the base. It has a longitudinal groove down the center on the upper surface with a corresponding keel on the lower surface. INFLORESCENCE: 8-10 in. (20-25 cm ) long. The rather stiff, erect-arching peduncle emerges from the base of the pseudobulb along the longitudinal fold in the leaflike sheath. FLOWERS: 8-14. Yellow blossoms are carried on a nicely spaced raceme along the upper half of the flower spike. Flowers are 0.8 in. (2 cm) across, 1 in. (2.5 cm) tall, and open fully. The triangular, sharply pointed sepals are bright yellow with a central reddish line. The large, almost round, bluntly tipped petals are cadmium yellow with fine red spots on the basal portion. The 3-lobed, cadmium yellow lip is wider across the sidelobes than across the midlobe. The pale brown callus is spotted with very small red dots. The green column has bright yellow wings marked with red spots. The anther is cadmium yellow. HYBRIDIZING NOTES: N/A. REFERENCES:. Braem, G. 1984. The genus Oncidium sect. Oncidium. Thesis at the University of Newcastle upon Tyne, England. Dodson, C., and D. Bennett, Jr. 1989. Orchids of Peru, Fasc. 2, plates 101-200. Icones Plantarum Tropicarum Series II. Missouri Botanical Garden, P. O. Box 299, St. Louis, Missouri 63166-0299. Dodson, C., and P. de Dodson. 1980. Orchids of Ecuador, Fasc. 2, plates 100-200. Icones Plantarum Tropicarum. Marie Selby Botanical Gardens, Sarasota, Fla. Hamilton, R. 1988. When does it flower? 2nd ed. Robert M. Hamilton, 9211 Beckwith Road, Richmond, B. C., Canada V6X 1V7. Copyright 1997, Charles O. Baker and Margaret L. Baker Sheet version 9267 ......................................................................... Please remember that this sheet is for your use only, and though it was provided free of charge, it may not be reproduced or retransmitted in any way without permission. ......................................................................... __________________________________________________________________________ "Orchid Species Culture" Charles & Margaret Baker, Portland, Oregon USA Orchid Culture & Pollination site http://www.orchidculture.com email <firstname.lastname@example.org> __________________________________________________________________________ "Orchid Species Culture Vol. 1 - Pescatorea, Phaius, Phalaenopsis, Pholidota, Phragmipedium, Pleione" 250 pages of culture information. "Orchid Species Culture Vol. 2 - Dendrobium" 850 pages of culture information for more than 1230 Dendrobium species. "The genus Paphiopedilum--Natural History and Cultivation" - Part 1 Dr. Guido Braem, Charles and Margaret Baker ISBN 0-9665337-0-4 Full page color photograph of each species. "The genus Paphiopedilum--Natural History and Cultivation" - Part 2 Dr. Guido Braem, Charles and Margaret Baker ISBN 0-9665337-1-2 Full page color photograph of each species. "Orchid Species Culture Vol. 3 - The Laelia/Cattleya Alliance" coming in a few months. __________________________________________________________________________