The sky is blue again over the school greenhouse but we have enjoyed a wet couple of days and our rain water tank has gone from very nearly empty to 1/3 full again. Our tank holds 16 000 litres and this month we have been down to our lowest level ever (about 1000 litres). We have been asked what we do if we run out of rain water but so far this has never happened. If we did run out of rain water we would have to use tap water but this would give us limescale deposits on all our leaves as well as reducing the amount we can feed safely in the summer (we can add more feed to rain water than tap water because the total dissolved salts level is so low in rainwater)
The hot spell has been a challenge for some of our cool loving plants as the greenhouse has regularly reached temperatures above 30C. Our policy is not to worry too much but make sure that plants are well watered so that they can cool with transpiration. A few plants have suffered from heat stress like this Masdevallia species which has dropped leaves
Some plants however have loved the extra warmth and our Renanthera imschootiana will be flowering for a second time this summer which has never happened before.
Dendrobium nolile is one of our favourite species and this week we have the pure white form in full flower. The more usual colour form is shown below.
The plant here flowering near Gangtok in Sikkim shows the natural growth habit. The plant grows long upright pseudobulbs during the warm wet summer months. In their second year these bulbs become less upright and produce heavy flowering in April. In their third year the bulbs are pendulous and produce a few extra flowers and by this time they have lost all their leaves.
The wild plants in Sikkim show a wide range of colour forms and one tree in particular demonstrated the variability of the species with dark forms, light forms, rounded flowers and more pointed flowers but we have yet to find the pure white var.virginalis. (see below) The tree also shows the habitat clearly with plants growing in dappled shade from tall trees and a little moss on the trunk showing that the dry season is far from bone dry here. In fact we found that it rains every few days in the dry season at this altitude 1200m. In cultivation we grow the species in Cool Asia with a minimum of 10C in winter and vents open above 17C. We keep the plants wet in summer and damp in winter, never allowing bulbs to shrivel.
Dendrobium nobile in SikkimThe species is found across a wide range in the Himalayas through to South East Asia. In Arunachal Pradesh (the extreme North Eastern state of India) we have seen the species growing on trees and on rocks as well as fallen plants used to adorn Buddhist temples and gompas. (below)
One of our plants is a real specimen and flowered to its full potential in 2013 when it won a Cultural Certificate from the RHS and produced one of my favourite orchid project photos. The plant may be even better than this next year as it is full of flowering potential now that it has become settled in its larger basket.
This beautiful species is endemic to Colombia where it grows in cloud forest above 2000m. Authorities describe the species as producing 30cm spikes with up to seven flowers but our clone produces spikes to 70cm with up to twelve flowers. Leading bulbs produce a number of spikes and give a fantastic display of the large and colourful flowers.
We grow our plants cool (minimum 12C) and damp all year.
This species is a reliable flowerer with very long lasting flowers.
This species is small warm growing and has been listed as a new species Dendrobium tanii by some authorities but is generally considered a variety of Dendrobium bracteosum.
Dendrobium bracteosum var tanii is a much more compact grower than other varieties of Dendrobium bracteosum and appears to be found only on the Maluku (Mollucas) Islands of Indonesia. It is found in a wide range of colour forms and ours start out deep pink and fade to light pink with age. The species is restricted to lowland forests and mangrove and so it enjoys warm temperatures in our Warm Asia section.
We grow the species mounted and each year it produces longer bulbs and so we are looking forward to seeing its full potential in the future. It repeat flowers from older bulbs that have lost their leaves and the flowers are very long lived.
This is a large growing species with a wide natural range including Borneo, the Lesser Sunda Islands, the Moluccas, The Philippines, Sulawesi, the Solomon Islands, the Bismark Archipelago, Papua and New Guinea, Fiji and Santa Cruz Islands. The species is restricted to areas near the coast up to 100m and so enjoys a hot climate and bright light.
We do our best to replicate the natural habitat by growing plants high in Warm Asia (Min 17C) but the species would enjoy higher temperatures and we keep plants drying in the winter to avoid damage on cooler nights.
The flower spike this year is over 1m long with around 100 flowers each 4cm across and it makes a terrific sight.