ORCHID SPECIES CULTURE
Charles and Margaret Baker

Aerangis luteo-alba (Krzl.) Schltr. var. rhodosticta (Krzl.) J. Stewart

AKA: Angraecum mirabile Hort, Angraecum rhodostictum Krzl., Angraecum
albido-rubrum De Wild., Aerangis albido-rubra (De Wild.) Schltr., Aerangis
rhodosticta (Krzl.) Schltr.

ORIGIN/HABITAT: Africa. The species grows across equatorial Africa from
Cameroons and the Congo Republic in the west through the central and
western forests of Uganda to Somalia, Ethiopia and Kenya in the east. In
Kenya, the plants are usually found at 3000-5000 ft. (910-1520 m) on the
southern and southeastern slopes of Mt. Kenya and on the southern slopes
of Mt. Elgon. Aerangis rhodosticta grows in warm, moist conditions, almost
always in forests along rivers. Plants normally grow in areas well
protected from drought, often near waterfalls. They usually grow on twigs
and branches of shrubs, but are occasionally found on tree trunks.

CLIMATE: Station #63720, Embu, Kenya, Lat. 0.5S, Long. 37.5E, at 4899 ft.
(1493 m). Record extreme temperatures are not available for this location,
but other stations in the region indicate record extremes near 90F (32C)
and 45F (7C).

N/HEMISPHERE    JAN  FEB  MAR  APR  MAY  JUN  JUL  AUG  SEP  OCT  NOV  DEC
F AVG MAX        70   72   76   78   75   75   78   81   81   77   74   73
F AVG MIN        56   56   57   58   58   56   56   57   59   61   60   57
DIURNAL RANGE    14   16   19   20   17   19   22   24   22   16   14   16
RAIN/INCHES     0.8  1.6  1.3  6.7  9.4  2.6  0.7  0.4  3.5 12.8  6.7  1.0
HUMIDITY/%      N/A
BLOOM SEASON      *        **   **    *                   *    *    *    *
DAYS CLR        N/A
RAIN/MM          21   40   33  169  238   67   18    9   89  325  171   26
C AVG MAX      21.3 22.0 24.5 25.7 23.9 23.8 25.4 27.1 27.5 25.0 23.5 22.5
C AVG MIN      13.2 13.2 13.8 14.7 14.6 13.5 13.5 13.8 14.9 15.8 15.4 14.0
DIURNAL RANGE   8.1  8.8 10.7 11.0  9.3 10.3 11.9 13.3 12.6  9.2  8.1  8.5
S/HEMISPHERE    JUL  AUG  SEP  OCT  NOV  DEC  JAN  FEB  MAR  APR  MAY  JUN

Cultural Recommendations:
The following recommendations are based on averages in the habitat. They
may be used as a guide for newly acquired plants whose requirements are
unknown, or for plants that are not growing or flowering as well as they
should. Reports from growers are included when they indicate success with
conditions in cultivation that are outside the range found in the habitat.

LIGHT: 1200-2000 fc. This species grows well with indoor window sill or 
artificial light culture. When fluorescent lights are used, growers report
success placing plants 6-9 in. (15-23 cm) below the lights.

TEMPERATURES: Summer days average 75-81F (24-27C), and nights average
56-57F (14C), with a diurnal range of 19-24F (10-13C).

HUMIDITY: Averages are not available for this location. Records from
nearby stations indicate that over the region averages are 70-75% most of
the year, dropping to near 65% for a short period in early spring. In late
summer, values increase for a short period before falling to 55-60% for 3
months. However, conditions may well be more humid in the riverine forests
of the habitat than is indicated by the data recorded at weather stations.

WATER: The double wet - double dry rainfall pattern depicted in the
weather data is common throughout the equatorial regions. The wet seasons
occur in spring and autumn, while winter is the primary dry season with a
secondary dry season occurring in summer. It is not known whether or not
the double rainfall cycle is important to the health or blooming of this
species. However, it does play an important role as the bloom trigger for
other plants that originate in areas with the same rainfall pattern.
Cultivated plants should be kept moist during periods corresponding to the
wet seasons. They should be allowed to dry slightly between waterings
during the dry seasons, but should never dry out completely or be left dry
for extended periods. For mounted plants, Fred Hillerman recommends that
plants be misted 5 times a week except in winter or during rainy weather.
If the weather is hot, plants should also be drenched daily, or soaked
(dunked) 3 times a week.

FERTILIZER: A balanced fertilizer, mixed at 1/4-1/2 recommended strength,
should be applied weekly during periods of active growth. Many growers use
a fertilizer with lower nitrogen and higher phosphate in autumn. If pots
are used, the medium should be leached every few weeks to prevent salt
buildup, especially when fertilizer is being applied most heavily. Plants
should first be watered normally to dissolve any accumulated salts. An
hour or so later, the medium is flushed with water equal to about twice
the volume of the pot. Year-round leaching is important in areas with
heavily mineralized water.

REST PERIOD: Winter days average 70-73F (21-23C), and nights average
56-57F (13-14C), with a diurnal range of 14-16F (8-9C). Rainfall is low
during a 4 month period in winter and for 2 months in summer. However,
high humidity in the stream-side habitat and nightly cooling results in
some moisture being available from dew. In cultivation, these conditions
may be simulated by early morning mistings, with thorough waterings given
every two weeks or so. Plants should be watched carefully for signs of
stress while water is reduced, particularly in summer. Water should be
increased if such signs appear.

GROWING MEDIA: Plants seem to grow better when mounted on slabs of cork
with a pad of sphagnum under the base of the plant. Some growers have
reported plants have not grown well when tree-fern slabs were used. If
plants are mounted, humidity must be high. In addition, mounted plants
must be misted at least once daily during most of the year, and several
mistings may be required on the hottest days of summer. If pots must be
used, a very open medium that allows good air movement around the roots
should be used. Medium or large sized fir bark works well with adult
plants for some growers. However, seedlings seem to grow better with less
root loss if a looser mix of sponge rock or coconut fiber is used instead
of a seedling mix based on fir bark. Undersized clay pots should be used.
Repotting should be done just as new root growth is starting in order for
the plant to become established as soon as possible.

MISCELLANEOUS NOTES: The bloom season in the table is based on cultivation
reports. In nature, plants with off-white or yellowish flowers grow east
of the Rift Valley. They bloom from midsummer into autumn. Those with pure
white flowers grow west of the Rift Valley and bloom in early summer.

Plant and Flower Information:

PLANT SIZE AND TYPE: A small, usually pendulous, monopodial epiphyte that
is almost stemless. The short stem is hidden by the basal sheaths of
closely set leaves. The roots are often flattened, with thin velamen, are
green when wet, and have emerald green tips.

PSEUDOBULBS: N/A. 

LEAVES: 6-10. The narrowly strap-shaped leaves are bright green, usually
less than 6 in. (15 cm) long, and are succulent and fragile.

INFLORESCENCE: 2-3 inflorescences that are usually pendulous, and may
reach 15 in. (38 cm) in length, emerge from the lower leaf axils.

FLOWERS: 6-25 on each inflorescence. They are produced in 2 rows on a
single plane. The 1-2 in. (2.5-5.0 cm) flowers are long lasting, but are
not fragrant. They open very flat, and are well spaced on the
inflorescence, which gives the plant a very neat and tidy appearance.
Color varies from pure white to ivory white, cream, or pale yellow. The
column is bright scarlet or vermilion, which creates a very striking
contrast.

HYBRIDIZING NOTES: Chromosome count is 2n = 42. The orange-red column of
this species is dominant when used in hybridizing.

REFERENCES: 

Beaton, C. 1985. Indoor light culture for Aerangis rhodosticta. American
Orchid Society Bulletin, 54(8):963. 

Bechtel, H., P. Cribb, and E. Launert. 1980. Manual of cultivated orchid
species. MIT Press, Cambridge, Mass.

Cavestro, W. 1980. Aerangis rhodosticta (Krzl) Schltr. - An African pygmy.
American Orchid Society Bulletin, 49(5):509. 

Hawkes, A. D. (1965) 1987. Encyclopaedia of cultivated orchids. Faber and
Faber, London. 

Hillerman, F. 1986. Growing Aerangis Orchids. American Orchid Society
Bulletin, 55(8):803.

Hillerman, F. E., and A. W. Holst. 1986. An introduction to the cultivated
Angraecoid orchids of Madagascar. Timber Press, Portland, Ore.

Northen, R. T. 1980. Miniature orchids. Van Nostrand Reinhold, New York.

Piers, F. 1968. Orchids of East Africa-Nairobi, Kenya. Verlag von J.
Cramer, 3301 Lehre. 

Stewart, J. 1984. Growing Angraecoid orchids - Part 1 - Introduction.
American Orchid Society Bulletin, 53(7):731. 


Copyright 1997, Charles O. Baker and Margaret L. Baker
Sheet version 564485

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

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