By the Orchid Man’s Son
JOS Member Nguyen Lee recently displayed his very nice Dendrobium (Den.) speciosum at the March 2021 JOS General Meeting. I’ve seen larger, but Nguyen explained that he grew it here in the Jacksonville area and left it outside all year-round. That got my attention. You see, like the early growers of this orchid in Australia and elsewhere (Mils, 2010), I’ve never been able to bloom this orchid. I have had Den. speciosum since 2014 and still no luck. Obviously, I’ve been doing something very wrong, and it is time to examine the culture requirements of this plant in greater detail.
Looking into this orchid reveals Den. speciosum, rather than being a single species is actually a complex of related orchids varying between 4 and as many as 15 varieties depending upon which authority you cite (see Baker and Baker, 1996; Lavarack, et. al, 2000; and Orchid Wiki, n.d.). Nguyen labeled his orchid as simply Den. speciosum with no other identifier, but I’ll assume his is Den. speciosum var. grandiflorum based upon its appearance. Fema Mankinen also entered a similar orchid but of a different variety, Den. speciosum var. pendunculatum. In contrast, while I do not have Den. speciosum such as Nguyen’s, I have a Den. speciosum var. pendunculatum as well as Den. speciosum var. grandiflorum. Together all three orchids share similar culture requirements although there are differences.
Originating in Southeast Australia from near the coast to as far as 150 miles inland, this orchid complex is a member of Dendrobium section Dendrocoryne and are popularly cultivated in Australia and elsewhere. The popular computer program OrchidWhiz showed no variation in the culture requirements for Den. speciosum, Den. speciosum var. grandiflorum, or Den. speciosum var. pendunculatum. However, Lavarack, et. al (2000) and the Bakers’ 1996 reference on Dendrobium culture do note small differences in requirements.
We’ll first look at the general cultural requirements for Den. speciosum as reported in OrchidWhiz and attributed to Baker and Baker. Afterwards we’ll identify any differences in culture for Den. speciosum var. grandiflorum and Den. speciosum var. pendunculatum.
Den. speciosum Culture Requirements
Den. speciosum generally requires high light (3000 – 4500-foot candles [fc]) and some varieties can be grown in full sun. I recommend starting in bright shade to see how well your example handles the light and move to brighter conditions if warranted. Further, Baker and Baker note that bright light is needed during the winter to support blossom bud development. Strike 1 … I missed on that issue and did not give mine enough light.
Den. speciosum receives rain most of the year in its native environment. However, it is probably greater in forested areas. The Bakers recommend that cultivated “plants should be watered frequently while actively growing with only slight drying allowed between waterings. “ Strike 2 … I missed on that issue as well and didn’t water my Den. speciosum enough during the growing season.
Den. speciosum is categorized by the Bakers and others as being cool to warm growing orchids with a high temperature of only about 70F and low temperatures of about 50-55F. As with most orchids, air movement should be strong throughout the year.
Den. speciosum is an interesting orchid in that it is found as both an epiphyte and a lithophyte (rock dweller) (Wikipedia, 2021). Reading between the lines, this means that different varieties of Den. speciosum have different requirements. Like many other orchids, this orchid can be mounted or grown in a pot. The proviso is that if mounted, they must be watered at least once daily during hot summer weather. Also similar to other orchids this orchid should be potted in an open and fast draining medium and should never be over-potted. Do not remove old stems as they will continue blooming for several years.
Den. speciosum is like many other orchids in that they require a rest after the growing season. Moreover, very bright light is needed in winter for flower bud development. Water should also be reduced after new growths mature in autumn. Strike 3 – I didn’t provide a rest for my Den. speciosum, no rest, no blooms. Further, the rest is probably the key component that was missing as I tried to bloom this orchid.
Den. speciosum Variety Peculiarities
Various authors note that the varieties of Den. speciosum have been renamed as their own separate species. They then observe that those reassignments have not been universally approved.
Den. speciosum var. pendunculatum
Jay Phal’s Orchid Species.com website lists this orchid as Den. pendunculatum although the Bakers and Orchid Whiz do not make this distinction. Further he notes this is “a small sized, hot growing lithophyte” and should be grown in full sun. It should also have water significantly reduced until new growth is seen in the spring.
Den. speciosum var. grandiflorum
Jay Phal’s Orchid Species.com website lists this orchid as Den. rex and states it is “a large sized, cool to warm growing epiphyte on trees in rainforests or lithophyte.” Generally, this speciosum type requires less direct light than other members of this complex. Grow this one similar to other Den. speciosum but with bright light and a drier period in winter and spring.
Baker, M. L., and Baker, C. O. 1996. Orchid Species Culture. Dendrobium. Portland, OR.: Timber Press.
Dendrobium speciosum. 2021. Retrieved 17 March 2021 from Wikipedia, https://en.wikipedia.org/wiki/Dendrobium_speciosum
Dendrobium speciosum. n.d. Retrieved 17 March 2021 from Orchids Wiki, https://orchids.fandom.com/wiki/Dendrobium_speciosum.
Field, L. 2003. The Dendrobium Speciosum Complex. The Orcadian, V 14 (2), p. 64-71. Retrieved 17 March 2021 from http://members.optusnet.com.au/elanbee/Den_speciosum_Len%20Field.pdf.
Lavarack, B., Harris, W., and Stocker, G. 2000. Dendrobium and its relatives. Portland, OR.: Timber Press.
Mils, C. 2020. Dendrobium speciosum_ Sm. Hortis Camdenensis. Retrieved 17 March 2021 from https://hortuscamden.com/plants/view/dendrobium-speciosum-sm.
Orchid Whiz. 2021. See https://www.orchidwiz.com
Phal, J. n.d. Dendrobium pendunculatum. Retrieved 17 March 2021 from http://www.orchidspecies.com/denpedunculatum.htm.
Phal, J. n.d. Dendrobium rex. Retrieved 17 March 2021 from http://www.orchidspecies.com/denrex.htm.