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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 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. 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