ORCHID SPECIES CULTURE
Charles and Margaret Baker

Oncidium wentworthianum Bateman ex Lindley. 

AKA: Oncidium tenue Lindley. 

ORIGIN/HABITAT: Mexico and Guatemala. In Mexico, plants are found in the
States of Vera Cruz and Chiapas. In Guatemala, they are found in the
mountains of Santa Rosa. Plants grow as epiphytes in humid forests at
elevations up to 4900 ft. (1500 m). 

CLIMATE: Station #76781, Minatitlan, Mexico, Lat. 18.0N, Long. 94.5W, at
90 ft. (27 m). Temperatures are calculated for an elevation of 4500 ft.
(1370 m), resulting in probable extremes of 91F (33C) and 35F (2C). 

N/HEMISPHERE    JAN  FEB  MAR  APR  MAY  JUN  JUL  AUG  SEP  OCT  NOV  DEC
F AVG MAX        61   65   68   71   74   72   71   71   70   68   64   61
F AVG MIN        51   52   54   55   58   58   59   58   58   56   53   52
DIURNAL RANGE    10   13   14   16   16   14   12   13   12   12   11    9
RAIN/INCHES     3.4  2.5  1.5  1.9  3.7  9.4 10.7 12.1 20.0 14.9 17.6  4.1
HUMIDITY/%       90   88   85   82   82   86   87   87   88   87   88   90
BLOOM SEASON           *              *   **  ***   **    *    *         *
DAYS CLR        N/A
RAIN/MM          86   64   38   48   94  239  272  307  508  378  447  104
C AVG MAX      16.1 18.3 20.0 21.7 23.3 22.4 21.7 21.7 21.1 20.0 17.8 16.1
C AVG MIN      10.6 11.4 12.5 13.0 14.7 14.7 15.2 14.7 14.7 13.6 11.9 11.4
DIURNAL RANGE   5.5  6.9  7.5  8.7  8.6  7.7  6.5  7.0  6.4  6.4  5.9  4.7
S/HEMISPHERE    JUL  AUG  SEP  OCT  NOV  DEC  JAN  FEB  MAR  APR  MAY  JUN

Cultural Recommendations: 

LIGHT: 2500-3500 fc. High light may be necessary to initiate blooms, but
plants should not be exposed to direct midday sun. Strong air movement
should be provided at all times. 

TEMPERATURES: Summer days average 71-72F (22C), and nights average 58-59F
(15C), with a diurnal range of 12-14F (7-8C). These temperatures represent
about the coolest conditions under which this species should be grown.
Because of the range in habitat elevation, plants should adapt to
conditions somewhat warmer than indicated. 

HUMIDITY: 85-90% most of the year, dropping to near 80% in spring. 

WATER: Rainfall is moderate to heavy almost all year, but conditions are
slightly drier for 2-3 months in late winter and early spring. Cultivated
plants should be watered heavily while actively growing; but their roots
should be able to dry rapidly after watering, and the medium should never
be allowed to become stale or soggy. 

FERTILIZER: 1/4-1/2 recommended strength, applied weekly while 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: Winter days average 61-65F (16-18C), and nights average
51-52F (11C), with a diurnal range of 9-13F (5-7C). O. wentworthianum
should adapt to conditions somewhat warmer than indicated. Winter rainfall
remains rather high in the habitat, but water should be reduced somewhat
for cultivated plants, especially those grown in the dark, short-day
conditions common in temperate latitudes. Plants should not be allowed to
dry out completely, however. Tomlinson (see references) reported that
these plants do not go through the same dormant period required by many
oncidiums and, as a consequence, need to be watered all year, although
water should be reduced in the colder winter months. Fertilizer should be
reduced or eliminated until new growth starts and heavier watering is
resumed in spring. 

GROWING MEDIA: Plants may be mounted on tree-fern or cork slabs if
humidity is high and plants are watered at least once daily in summer.
Several waterings a day may be necessary for mounted plants during very
hot, dry periods. Because most growers find it difficult to keep mounted
plants moist enough, they are usually grown in pots using a very open,
fast draining medium such as medium sized fir bark. Materials such as
perlite that help hold the medium open and also retain some moisture are
often added to the fir bark. Charcoal is often added to help keep the
medium open and prevent it from becoming sour. Plants should be repotted
when the medium starts to break down or when the plant has outgrown its
pot. Repotting should be done just as new root growth is starting to
enable the plant to become re-established in the shortest possible time
before the added stress of hot, dry, summer weather. This is usually after
flowering in late winter or early spring. 

MISCELLANEOUS NOTES: The bloom season shown in the climate table is based
on cultivation records. 

Plant and Flower Information:

PLANT SIZE AND TYPE: A large sympodial epiphyte to 17 in. (43 cm) tall. 

PSEUDOBULB: Usually 3-4 in. (7.5-10.0 cm) long, but pseudobulbs may be as
large as 5 in. (12.7 cm). They are clustered, robust, ovoid-oblong,
somewhat compressed, and become furrowed with age. They are dark green,
but they are typically transversely barred with bands of tiny brown spots.
They have thin, dry, fibrous sheaths at the base. 

LEAVES: 5-14 in. (13-35 cm) long by 0.6-1.1 in. (1.5-2.8 cm) wide. There
are usually 2 rather leathery, sharply pointed leaves at the apex of each
pseudobulb. 

INFLORESCENCE: Usually up to 39 in. (100 cm) long, but the arching, wavy,
branching inflorescence may be as long as 84 in. (213 cm). The slender
branches of the panicle may be short or rather elongated and are spaced
well apart. The longer ones may then be branched again. The peduncle
emerges from the base of the pseudobulb and is subtended by a leaflike
sheath. 

FLOWERS: 3-10 relatively large, showy blossoms are carried on each branch
of the panicle. The flowers are usually about 1 in. (2.5 cm) across. The
spreading-reflexed sepals and petals are deep yellow, irregularly blotched
with red-brown, and have undulate margins. The lip has pale yellow,
rounded sidelobes and a yellow midlobe with some red-brown spots around
the crest. 

HYBRIDIZING NOTES: Chromosome count is 2n = 56. 

REFERENCES: 

Ames, O. and D. Correll. (1952-1965) 1985. Orchids of Guatemala and
Belize. Dover Publications, New York. 

Hamilton, R. 1988. When does it flower? 2nd ed. Robert M. Hamilton, 9211
Beckwith Road, Richmond, B.C., Canada V6X 1V7.

Hawkes, A. [1965] 1987. Encyclopaedia of cultivated orchids. Faber and
Faber, London. 

Tanaka, R., and H. Kamemoto. 1984. Chromosomes in orchids: counting and
numbers. Appendix in Orchid biology: reviews and perspectives, vol. III.
J. Arditti, ed. Comstock Publishing, Cornell University Press, Ithaca,
N.Y.

Tomlinson, P. Not dated (1986?). Oncidiums --a cultural guide. Wellington
Orchid Society, Inc., 5 Norwich Street, Wellington, New Zealand. 

Williams, L. [1951] 1986. The Orchidaceae of Mexico. CEIBA 2(1-4):1-256. 

PHOTOS/DRAWINGS: . 


Copyright 1997, Charles O. Baker and Margaret L. Baker
Sheet version 546395

.........................................................................
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 <cobaker@troymeyers.com>
__________________________________________________________________________

    "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.
__________________________________________________________________________