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.
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 "Orchid Species Culture" Charles & Margaret Baker, Portland, Oregon USA

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