Growing Conditions for Orchids
The ideal growing conditions for orchids are provided by abuilt against a house wall. It will draw some heat from the wall, and if the house has central heating an extra radiator could be fixed inside the conservatory to provide cheap winter heating.
A smallis quite adequate for growing orchids, provided it can be maintained at a winter temperature of 7°C (45°F), is clean and free from fungal diseases, which can wipe out a valuable collection very rapidly. An electric extractor fan, 25-30cm (10-12in) in diameter, is the best way of ventilating the greenhouse. Install this in the wall opposite the entrance door, about 1.8m (6ft) from the ground.
There should also be a bottom ventilator in the base of the entrance door. It will need a sliding or hinged shutter to help control air flow and humidity.
A small number of tropical orchids, which need very warm conditions, can be grown economically in a cool greenhouse by keeping them in a fairly tall glass frame on the staging. A frame with bottom heating should provide enough heat, but if necessary it can be lined on the inside with plastic sheeting for extra insulation during winter.
Fix the plastic sheeting to wooden supports around the sides and top of the frame, leaving a 2.5cm (lin) space between plastic and glass. In summer, remove the plants from the frame and keep them in the warmest part of the greenhouse. At least six tropical orchids would fit into a frame 60 x 60cm (2 x 2ft) wide and 90cm (3ft) tall.
An alternative is to construct a glazed partition at the end of the greenhouse, forming a cubicle which can be kept warmer and more humid This can provide quite a large area for tropical orchids. During the winter, line the area with plastic sheeting mounted on wooden frames. Remove the plastic in spring when maximum sunlight is needed.
Another place to grow tropical orchids is indoors, in a miniature greenhouse. The ‘greenhouse’ is a small glazed frame standing on a large window-sill over a central-heating radiator. If possible, keep the frame in a north or east-facing window in summer, and in a south or west-facing window in winter. Cultural requirements are the same as for greenhouses, butis crucial as temperature changes are more rapid in a small space.
Most orchids can be divided into either cool greenhouse types, such as Coelogyne, Cymbidium and Pleione, or warm greenhouse (tropical) types, such as Miltonia and Phalaenopsis.
The cool greenhouse plants need a minimum temperature of 7°C (45°F) in winter and 14°C (57°F) in summer. Tropical orchids need a minimum temperature of 16°C (61°F) in winter — although they will tolerate brief, cooler periods —and 22°C (72°F) in summer. However, many commonly grown orchids, such as Cattleya, Dendrobium, Odontoglossum and some
Paphiopedilum species tolerate temperatures intermediate between these two ranges.
To provide the heat, an electric fan heater with a thermostatic control is ideal as it keeps the air moving. A 3kW heater will keep a 3 x 2.4m (10 x 8ft) greenhouse warm enough for cool-house orchids. A 4-1/2kW heater is needed in the same size greenhouse for tropical orchids.
To grow tropical orchids in a separate section of a 3 x 2.4m (10 x 8ft) cool greenhouse, you would need an additional smaller heater in this section.
Keep a paraffin heater as a safeguard against power failure.
In their, many orchids grow in areas where water vapour rises from the damp ground or foliage around them. They absorb moisture through their leaves and roots.
This humidity is produced in the greenhouse by spraying water frequently on the flooring and on the staging where the plants stand. Light but frequent damping down is more effective than occasional flooding.
In summer, damp down the orchid house at least once a day — in the morning — and preferably again in the late afternoon or evening. If the weather is particularly hot, three or four dampings may be necessary, as well as mist spraying of the foliage.
In winter, two or three dampings a week are sufficient, before midday. Do not damp down if the outside temperature drops below freezing.
The easiest method of damping down the staging is to use tap-water applied through a hose with a fine-spray nozzle. Do not spray the water on the flowers or bulb bases. This can be avoided by standing the plants permanently on up-turned flower-pots. When tropical orchids are grown in a frame, damp down with a syringe filled with collected disease and pest-free rainwater.
Automatic damping down systems can be installed, which provide a fine mist at intervals from a spray line according to instructions received from computerized humidity sensors, but these are expensive to install.
Fresh air is essential to all orchids, but it must be provided without causing a draught or lowering the temperature or the humidity. A close, muggy atmosphere encourages fungal diseases.
A 25-30cm (10-12in) extractor fan will draw in enough air through gaps around the door to ensure adequate ventilation, and a ventilator at the bottom of the greenhouse can be opened to increase air flow in hot weather.
Fans can be connected to a thermostat, so that they come on automatically when the temperature of the house becomes too high.
The cheapest form of ventilation is by the traditional ventilators fitted to the top and bottom of the greenhouse on both sides. It is preferable to have one top vent and one bottom vent on each side of the orchid house for every 1.2m (4ft) of its length. Bottom ventilators should be at least 30 x 60cm (1 x 2ft), and covered with fine-mesh wire netting to keep out pests.
During summer, open the top vents on the leeward side by 10- 15cm (4-6in) day and night. On very hot days, also open the bottom ventilators on the same side. With below average temperatures, close all ventilators.
In winter, close the top ventilators to retain the warm air, and open the bottom vents on the leeward side to allow fresh air into the greenhouse.
To prevent the temperature inside the greenhouse from rising too high in summer, the greenhouse must be shaded.
The best — but most expensive —form of shading is provided by roller blinds made of wooden or plastic laths. Plastic fabric roller blinds, which are run up and down the roof, provide cheaper shading.
Leave an air space between the glass and the blinds to allow air to circulate over the surface of the glass and so keep an even temperature in the greenhouse. Unroll the blinds on the sunny side of the greenhouse whenever the sun shines brightly during late spring and summer
A less satisfactory method of shading is to paint the greenhouse glass with whitewash or special electrostatic shading paint. Apply a thin coat in late winter and then another coat on top in mid spring. Wipe off the whitewash in early autumn.