In complete contrast to yesterdays miniature Platystele we have a giant Coelogyne today.
This species is a large grower with 10cm pseudobulbs each topped with two dark green leaves and a long flower spike of six to twelve large attractive flowers. The species is native to the Himalayas where it is reported from Nepal through Sikkim, Bhutan and Arunachal Pradesh through to Yunnan. We have seen the species flowering in the tops of trees in wet semi-evergreen forests at 2000m in Arunachal Pradesh (photo below). The orchid is the large green leaves and yellow bulbs in the centre of the photo and the image next to it shows the semi-evergreen forest habitat.
The plant in the wild is flowering really well in its exposed position.
Specimens in the wild can become really large plants enveloping sections of the trunk or main branches of large trees and our specimen at school has grown into a very large size since arriving as a single bulb in 1993. We grow the plant in Cool Asia (minimum 10C) and keep it well watered throughout the year especially in the summer. The plant now has a verdant layer of natural moss around the base of the pseudobulbs.
We are always keen to take specimen orchids to the RHS London Orchid Show and the cancelled show this week would have been perfect timing for this ‘miniature specimen’
The plant shown has now completely filled its 8cm basket and produces a multitude of little starry flowers about 2mm across from the bright green 2cm leaves. Does anyone fancy counting the flowers? I estimate that there are 107 flower spikes this year and that each has on average eight flowers open and another seven in bud. An amazing thing. When it finished flowering it will be time to split it up and I hope that we will have over fifty plants in flower to offer in a years time.
This tiny miniature is native to cloud forests in Colombia at around 2000m and enjoys a shady spot with heavy watering throughout the year. The flowers are amazingly long lasting and we expect this plant to still be in full flower in two months time.
We grow plants successfully in pots and baskets and expect they would do well mounted to. Plants bulk up quickly so all in all a lovely little species to grow.
Two years ago the plant shown looked like this (photo below) showing just how quickly the species can grow when really happy.
Last year it was this big
We have seen several Platystele species in their natural habitats and most have been tiny miniatures but all have had charming starry flowers. The smallest species of orchid we have found on any of our trips was this Platystele compacta in Costa Rica. The whole plant is less than 2cm across.
Platystele compacta in Costa Rica
With the warm April sun starting to have an impact it is time to shade your orchid house if like me you grow cool tropical species in a greenhouse at home.
Inside, these are all species native to the cool mountains of Central and South America, or the Himalayas so the temperature ranges from a minimum of 10C, to an ideal summer maximum below 30C. Keeping plants cool in the summer is not easy in a greenhouse. The main challenge for an orchid house to grow cool tropical species is keeping temperatures cool in the summer. Standard greenhouses are glass to ground and designed to provide natural warmth in the spring and then hot conditions in the summer for crops such as tomatoes. You can see how my greenhouse is modified for thermal stability.
Firstly the greenhouse has a block wall up to three feet with a chalk bank built against it – the wall also provides 4000 litres of rainwater storage. The next step is double glazing inside with corrugated plastic to keep heating costs to a minimum. Then there is the permanent hurdles which provide deep shade up to the eves, and finally the green roof shade net that went on yesterday.
I find that with a lean-to greenhouse the perfect arrangement for shade is to support it on wooded poles above the vents.
Inside there are of course different light levels available and so Cattleya coccinea that likes it bright is near the roof.
While mounted pleurothallis species have more shade lower down on the back wall
What a wonderful show we have in the greenhouse. Today would have been set up day for the London RHS Orchid Show, and I know several students who will be gutted today, not being there – me too. We will just have to make the 2021 show the best ever.
One species that would have had a big reaction from Show visitors is this dramatic species from the Himalayas.
Dendrobium densiflorum has to be one of the most dramatic orchids we grow, and we have been fortunate to see it flowering its natural habitat too. In Sikkim the species grows at around 1000m where it lives as an epiphyte generally in tall semi-evergreen trees with little moss as shown below. The high end of its range overlaps the lower end of Dendrobium nobile’s range and we have seen both species flowering together during April just as they do in our greenhouse,
We grow out plants mounted with heavy watering in the summer. This is one of the plants that section hops in the greenhouse to replicate its natural habitat. In the summer it grows its new pseudobulbs rapidly and we find it a home in Warm Asia where heat and heavy watering help it to grow long bulbs. Its native Sikkim becomes quite cool at 1000m in winter and so we move it for a fairly dry rest in Coll Asia from November until February. We then move it back to warm where the change in climate usually induces rapid flower development, taking about six weeks after the move.
Plants are very long lived and flower from older pseudobulbs so patience is required to grow a specimen – but it is well worth it.
This is, of course, the type specimen of Dendrobium section, densiflorum and it is interesting to contrast it with its very close relatives, also flowering in the greenhouse this week.
Her is D. dendiflorum with D. thyrsifloum – Dendiflorum doesn’t have much denser flower racemes but the plants are distinct apart from the obvious colour difference. Densiflorum has shorter, square sectioned bulbs, while thyrsiflorum has longer round sectioned bulbs. Dendrobium lindleyi (bellow) is much smaller than either densiflorum or thyrsiflorum.
Then there is Dendrobium chrysotoxum, (below) with much stouter bulbs and a much looser flower raceme.
What a great group of orchids.
It isn’t just Dendrobioums filling the greenhouses with flowers this week and Coelogyne pulverula has opened its first two, long (up to 100cm), pendulous, sprays of flowers in our Warm Asia section.
The species is native to Malaysia, Thailand and Borneo where it grows on the trunks and lower branches of large trees in evergreen forest from 300 to 1800m. We find that the species enjoys growing warm but well shaded and kept moist throughout the year. We find that leaves can become damaged by bright sun or by plants being allowed to become dry for long periods.
We saw a number of Coelogynes in the forests of Sarawak during our visits including Coelogyne motleyi in flower , in July, and and Coelogyne asperata (below) in October, and most were growing in shaded spots in the lower branches or on the trunks of trees where the large leaves are protected from too much intense equatorial sunshine.
The image below (Taken in the Mulu National Park), shows perfectly the natural habitat of Coelogynes such as C.pulverula.
You can also see that pendulous flower spikes are great for pollinator access as there is a good space below the plant.
The flowers do bruise quite easily and so it is worth moving a plant in spike to a safe place, like ours in the photo, for the flower spikes to grow where they won’t touch things or be knocked. There are another ten spikes in bud, so the plant will be providing a great display for weeks to come.