Dendrobium tapiniense and OTHER DENDROBIUMS of SECTION LATOURIA
by Paul Carver
Dendrobium tapiniense, a native of Papua New Guinea, is one of about fifty dendrobiums in Section Latouria, which is centred mainly in PNG, although a few species occur in the Philippines, Java, Fiji and Samoa. Other members of Section Latouria that I grow with some success are D. aberrans, D. alexandrae, D. atroviolaceum, D. eximium, D. forbesii, D. macrophyllum, D. normanbyense, D. rhodostictum, D. polysema and D. punamense. I also grow D. convolutum, D. engae, D. finisterrae, D. johnsoniae, D. otaguroanum, D. shiraishii and D. spectabile but with less success.
I grow all these dendrobiums in a heated house that is maintained at a minimum temperature of 12°C in winter, and a maximum of 30°C in summer. The relative humidity is kept between 70% and 80%, even on hot days, using two second-hand evaporative coolers. The air from these is further humidified with fine misters placed in front of their air outlets. Both coolers and their misters are coupled to a thermostat set so that they commence operation when the temperature reaches 28°C. An automatic overhead misting system also operates for sixty seconds at 10 am, noon, 2 pm and 3 pm. On really warm or hot days, I wet the scoria floor thoroughly if the relative humidity drops below 65%.
Phil Spence has explained to me that the roots of dendrobium species in Section Latouria do not like to remain wet for any length of time, and that some of the roots at the crown need to be exposed to the air. Obviously the potting mix that I was using retained too much moisture, so I now use a mix containing three parts of 10 mm orchid bark and one part of 10 mm quartz or similar stone. I no longer use perlite or charcoal in the mix. I also use the smallest possible squat pot that will accommodate the roots.
As to watering, I prefer to hand mist unless the pots appear to be dry, in which case they all receive a thorough watering. I know when my orchids are drying out if pots with a sphagnum-perlite mix feel dry on the surface. Also, by experience, the weight of a potted plant will indicate how much water is present.
Many dendrobiums in Section Latouria need high light, so I suspend my pots of D. tapiniense near the roof. However, high light is not necessary for all Latouria Section dendrobiums, as I had a great flowering of D. forbesii this season (five racemes, each bearing ten flowers), even though its pot had been placed on the bench at the southern, shady end of my intermediate house.
I use liquid fertiliser (Peters plus Calcium) at a concentration of no more than 400 mg per litre about once every fortnight. This concentration also suits other genera that I grow in sphagnum moss, rather than in a bark-based mix.
My plants of D. tapiniense suffered from serious fungal attack last year, the leaves becoming mottled with yellow and green striations and black necrosis. I sprayed with Alliette®, and although the unsightly leaves still remain, the new growths are clear of infection. Of course, these plants may take one to two years before they resume flowering. Once sufficient new, unblemished leaves have developed, I will cut off the unsightly ones.